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390 Cards in this Set
- Front
- Back
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purpose of embryonic folding for the digestive system
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incorporates both the gut tube and the coelom into the embryo, it creates the gut tube, as folding progresses the yolk sac gets pinched down to form a gut tube with a stalk (vitelline duct) connecting to the remaining yolk sac, the mucosa and glands of the GI tract arise from endoderm and the surrounding connective tissue and smooth muscle comes from splanchnic mesoderm of the lateral plate
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what portions of the endoderm-lined gut remain outside the embryo after folding
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yolk sac and the allanotis
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what part of the gut does the yolk stalk (vitelline duct) attach to?
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the midgut, the other two parts (foregut and hindgut) form the rest of the blind ending tube
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positioning of the pharyngeal gut
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extends from the buccopharyngeal membrane to the tracheobronchial diverticulum
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positioning of the foregut
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caudal to the pharyngeal tube and extends as far caudally as the liver outgrowth
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positioning of the midgut
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begins caudal to the liver bud and extends to the junction of the right 2/3s and left third of the transverse colon in the adult
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positioning of the hindgut
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extends from the left third of the transverse colon to the cloacal membrane
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what does endoderm give rise to in the digestive system
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forms the epithelial lining of the digestive tract and gives rise ot the parenchyma of glands (hepatocytes and the exocrine and endocrine cells of the pancreas
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what does splanchnic mesoderm give rise to in the digestive system
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stroma (connective tissue) of the glands, also muscle, CT and peritoneal components of the gut wall
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mesenteries
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the lining of the coelemic sacs from each side of the gut tube, are the pathways for vessels and nerves to reach abdominal organs, persist only where necessary, suspend structures from the dorsal and ventral body wall, formed from the joining of right and left splanchnic mesoderm layers
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dorsal mesentery
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found throughout, most of, the entire length of the abdominal gut tube, suspends the foregut, midgut and major part of the hindgut from the abdominal wall after the 5th week, extends from the lower end of the esophagus to the cloacal region of the hindgut, gives rise to greater omentum (dorsal mesogastrium) at the stomach, the mesoduodenum at the duodenum and the dorsal mesocolon at the colon, and mesentery proper at the jejunum and ileum
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ventral mesentery
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only found in the region of the foregut, exists only in the region of the septum transversum (terminal part of the esophagus, stomach and upper part of the duodenum
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septum transversum
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the mesodermal plate between the pericardial cavity and the stalk of the yolk sac
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greater omentum
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as the greater curvature undergoes expanded growth the dorsal mesentery needs to expand to accommodate both the growth and rotation, this expansion creates the greater omentum
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lesser omentum
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comes from the growth of the liever into the mesenchym of the septum transversum dividing the ventral mesentery into this, extends from the lower portion of the esophagus, the stomach and the upper portion of the duodenum to the liver
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falciform ligament
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like the lesser omentum, comes from the growth of the liever into the mesenchym of the septum transversum dividing the ventral mesentery into this, extends from the liver to the ventral body wall
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do the two coelemic sacs become continuous
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yes they do, when going from foregut to hindgut, in the foregut the ventral mesentery keeps thems separatte, as one travels inferior the ventral mesentery disappears and the two sacs form one
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peritonealization
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having mesentery around an organ, although most of the gut tube has a mesentery initially, some structures lose their mesentery during future development
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primarily retroperitoneal
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structures that never have a mesentery, (thoracic esophagus, rectum)
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secondarily retrperitoenal
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structures that once had mesentery, but lost it (pancreas, duodenum, ascending and descending colon)
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intraperitoneal
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structures covered with mesentery after further development (stomach, jejunum and ileum, cecum, appendix, transverse colon, sigmoid colon, gallbladder)
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vitelline artery
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comes from the SMA as it runs through the mesentery proper and continues toward the yolk sac
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specification of gut tube divisions
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different areas of the gut tube undergo differentiation based on the expression of homeobox genes in the mesoderm, factors in the mesoderm are upregulated by SHH expression from the endoderm of the gut tube
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respiratory diverticulum
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lung bud, forms at ~4 weeks at the ventral wall of the foregut at the border with the pharyngeal gut, eventually separated from the foregut by the trachoesophageal septum
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esophagus
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initially short but lengthens rapidly with the descent of the heart and lung, muscle coat formed by the surrounding splanchnic mesenchyme, striated in upper 2/3s and innervated by vagus, smooth in the lower 1/3 and is innervated by the splanchnic plexus
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rotation of the foregut
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stomach undergoes a 90 degree roation with the anterior surface turning to the right, stomach rotates along two axes, a longitudinal one (like a top, 90 clockwise, left side now faces anteriorly and the right faces posteriorly) and an anteroposterior one (like a pinwheel, causes the caudal or pyloric part to move to the right and up and the cephalic or cardiac portion to move to the left and down) when facing the anterior surface
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greater and lesser curvatures
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arise due to differences in growth between the original anterior (slower) and posterior portion (faster)
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omental bursa (less peritoneal sac)
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a space behind the stomach formed from rotation about the longitudinal axis pulling the dorsal mesogastrium to the left
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lienorenal ligament
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connects the spleen to the body wall in the region of the left kidney
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gastrolienal ligament
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connects the spleen to the stomach
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pancreas and its positioning in relation to the dorsal mesogastrium
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initially the pancreas grows into the dorsal mesoduodenum but eventually its tail extends into the dorsal mesogastrium, this portion eventually fuses with the posterior wall and only its anterior portion is covered with peritoneum making it retroperitoneal (secondarily)
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what happens at birth to the greater omentum and the transverse mesolcon
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they fuse with each other, two leaflets of the greater omentum fuse with each other as well forming a single sheet
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what do the liver cords form when they grow into the septum transversum
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the peritoenumeum of the liver, the falciform ligament and the lesser omentum
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umbilical vein
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found within the free margin of the falciform ligament, obliterated after birth to form the round ligament of the liver (ligamentum teres hepatis)
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hepatoduodenal ligament
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connects the duodenum and liver, contains the bile duct, portal vein and the hepatic artery (portal triad), also forms the roof of the epiploic foramen of Winslow (the opening connecting the omental bursa with the rest of the peritoneal cavity (lesser and greater sacs)
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duodenum
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formed from the terminal part of the foregut and the cephalic part of the midgut, takes on a C-shaped loop (when the duodenum rotates to the right) and is moved to the left (when the stomach rotates and the growth of the head of the pancreas), fixed in a retroperitoneal position when it is forced against the dorsal body wall, supplied by both the celiac and SMA
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duodenal cap
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portion of the duodenum that remains intraperitoneal, retains its mesentery of the mesoduodenum
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canalization in the duodenum
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during the 2nd month the lumen of the duodenum is obliterated by proliferation of cells in its walls, then undergoes recanalizaiton
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celiac artery
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supploies the foregut
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superior mesenteric artery
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supplies the midgut
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liver, gallbladder and ventral pancreatic bud attachment
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all three of these are attached at the same place on the duodenum, there is a separate dorsal pancreatic bud
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what does growth of the duodenum do to the positioning of the bile duct
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moves the opening of the bile duct around to the dorsal surface
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liver primordium
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appears in the middle of the 3rd week as an outgrowth (hepatic diverticulum, liver bud) of the endodermal epithelium at the distal end of the foregut
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liver bud (hepatic diverticulum)
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consists of rapidly proliferating cells that penetrate the septum transversum
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bile duct
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formed from the narrowing of the connection between the hepatic diverticulum and the foregut, combination of the cystic duct and the hepatic duct, as rotation occurs its positioning moves from an anterior position to a posterior one passing behind the duodenum
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gallbladder and cystic duct
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formed as a small ventral outgrowth from the bile duct
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cells of the liver
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epithelial liver cords form hepatic sinusoids and differentiate into parenchyma (liver cells) and form the lining of the bilary ducts, hematopoietic cells, Kupffer cells and covvective tissue cells are derived from mesoderm of the septum transversum
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visceral peritoneum of the liver
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derived from mesoderm on the surface of the liver, found everywhere except on its cranial surface (it remains in contact with the original septum transversum), this region leads to the formation of the central tendon of the diaphragm
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bare area of the liver
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area of the liver that remains in contact with the diaphragm and is never covered by peritoneum
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10th week of development and weight of the liver
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liver is 10% of the body weight
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hematopoetic function of the liver
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contains large nests of proliferating cells which produce red and white blood cells, accounts for about half of the 10% body weight, lie between hepatic cells and walls of the vessels, this activity declines during the last 2 months of intrauterine life and thus its weight nears the 5% mark of total body weight
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12th week of development and liver function
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liver begins creating bile, bile can enter the GI tract through the bile duct
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pancreas
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formed from two buds (ventral and dorsal), these buds emerge from the endodermal cells of the duodenum
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dorsal pancreatic bud
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found in the dorsal mesentery
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ventral pancreatic bud
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found near the bile duct, when the duodenum rotates to the right, the ventral bud moves near the dorsal bud coming to lie below and behind the dorsal bud eventually fusing, ventral bud leads to formation of the uncunate process and inferior portion of the head
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main pancreatic duct (of Wirsung)
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formed by the distal part of the dorsal pancreatic duct and the entire ventral pancreatic duct
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accessory pancreatic duct (of Santorini)
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formed from the proximal part of the dorsal pancreatic duct, is either obliterated or persists as a small channel
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major papilla
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site where the main pancreatic duct and the bile duct unite to enter the GI tract
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minor papilla
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site where the accessory pancreatic duct enters the GI tract
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pancreatic islets (of Langerhans)
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develops from the parenchymatous pancreatic tissue and scatter throughout the pancreas, develops during the third month of the fetal life, secretes insulin as well as glucagon and somatostatic-secreting cells
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insulin secretion
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begins at the 5th month of life
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midgut
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suspended from the dorsal abdominal wall by a short mesentery and communicates with the yolk sac by the vitelline duct, begins distal to the entrance of the bile duct into the dudodenum
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midgut rotation
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midgut loop is centered on the SMA with the cecum, ascending and transverse colon in the caudal half of the loop, rotation occurs in a counterclockwise direction (as you view the fetus from the anterior surface) around the SMA until it ends up inferior to it, completion of rotation takes place in the abdomen, causes the transverse colon to pass anterior to the duodenum and place it in its superior anterior position, found only in the small intestine, not the large
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primary intestinal loop
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the first intestinal loop, undergoes rotation in a counterclockwise manner, cephalic limb of the loop leads to the durodenum, jejunum and part of the ileum, the caudal limb becomes the lower portion of the ileum, the cecum, the appendix, the ascending colon and the proximal 2/3 of the transverse colon
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physiological herniation
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as the liver begins to rapidly grow and expand, the abdominal cavity does not have enough room to house all the loops of the intestine so they enter the extraembryonic cavity in the umbilical cord during the 6th week of development (physicological umbilical herniation), formation of the small intestinal loops and the formation of the cecum occur during the herniation, first 90 degrees of rotation occurs during herniation, the remaining 180 degrees occurs during the return of the gut ot the abdominal cavity (3rd month)
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retraction of the herniated loops
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starts at the 10th week, thought that regression of the mesonephric kidney, reduced growth of the liver and expansion of the abdominal cavity play important roles, proximal portion of the jejunum is the first part to reenter
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cecal bud
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appears at about the sixth week as a small conical dilation of the caudal limb of the primary intestinal loop, the last part of the gut to reenter the abdominal cavity, initially in the right upper quadrant below the right lobe of the liver then eventually pass to the right lower quadrant (to the right iliac fossa), leads to the ascending colon to be on the right side of the abdominal cavity
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vitelline duct and position relative to the cecum and ileum
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lies between the cecum and ileum, located in the ileum before the cecal bud
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appendix
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develops as a diverticulum of the cecum, develops during descent of the colon, final position is frequently posterior to the cecum or colon (retrocecal or retrocolic)
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mesentery proper
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mesentery of the intestinal loops, twists around the origin of the SMA when the caudal limb of the loop moves to the right side of the abdominal cavity
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ascending and descending colon and their mesentery
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when the ascending and descending colon reach their final position, their surrounding mesentery pushes against the abdominal wall forcing the ascending and descending colon into a retroperitoneal position (the appendix, lower end of the cecum and sigmoid colon remain intraperitoneal)
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transverse mesolcolon and its fate
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fuses with the posterior wall of the greater omentum but maintains its mobility, attaches to the hepatic and splenic flexures
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mesentery of the jejunoileal loops
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initially continuous with the mesentery of the ascending colon, when the ascending mesocolon fuses with the posterior wall the mesentery of the jejunoileal loops obtains a new line of attachment that extends from the area where the duodenum becomes intraperitoneal to the ileocecal junction
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volvulus
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any form of rotation of parts of the gut tube, can be dangerous because of potential for disrupting the blood supply and causing gangrene
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gastroschisis
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the lateral walls of abdomen do not close completely, the expanding GI tract protrudes through the opening, 1:10,000 occurrence, but very common in mothers who used cocaine during W4, usually spontaneous abortions protect the mother, because the herniation is lateral to the connecting stalk it is not covered by amnion, gastroschisis is usually not associated with chromosome abnormalities or other severe defects, so the survival rate of the infant after ~W35 is excellent
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omphalocele
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herniation of abdominal viscera through an enlarged umbilical ring, there was a failure of the intestinal loops to return to the body cavity, from the umbilical cord, after normal physiological herniation during W6-W10, that is why an omphalocele hernial sac is always covered with the epithelium of the umbilical cord, a derivative of the amnion, it is a common defect (1:2500 births), about half of the infacnts with this condition are stillborn
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rotation anomalies
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nonrotation-don’t get rotation so have cecum midline
mixed rotation + dudodenal volvulus-leads to a dilated duodenum and duodenal obstruction mixed rotation + transverse colon volvulus-can be caused by the SMA compressing the transverse colon causing a dilation in the ascending colon subhepatic cecum and appendix-these are their initial positions, do not descend properly internal hernia-seen when the jejunum and ileum pass through the hole, may lead to an internal hernial sac mixed roation + duodenal + transverse colon volvulus-may occur if the ascending colon moves anteriorly around the duodenum pinching it |
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reversed rotation of the intestinal loops
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occurs when the primary loop rotates 90 clockwise, the transverse colon passes behind the duodenum and lies behind the SMA
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duplications of intestinal loops and cysts
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may occur anywhere along the length of the gut tube, they are most frequently found in the region of the ileum where they may vary from a long segment to a small diverticulum
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formation of the anal canal
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endoderm forms the portion from the hindgut while ectoderm forms the portion form the protoderm
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hindgut
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gives rise to the distal third of the transverse colon, the descending colon, the sigmoid, rectum and upper part of the anal canal, endoderm also forms the internal lining of the bladder and urethra
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primitive anorectal canal
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where the terminal portion of the hindgut enters the posterior region of the cloaca (future anorectal canal)
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primitive urogenital sinus
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where the allantois enters into the anterior portion of the cloaca
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cloaca
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is an endoderm-lined cavity covered at its ventral boundary by surface ectoderm, this boundary forms the cloacal membrane
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urorectal septum
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a layer of mesoderm, separates the region between the allantois and the hindgut, comes to lie close to the cloacal membrane but never makes contact, at the end of the 7th week the cloacal membrane ruptures creating openings for the anorectal and UG sinus, tip of urorectal septum forms the perineal body
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canalization of the anal canal
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proliferation of the ectoderm closes the caudalmost region of the anal canal, during the 9th week it recanalizes
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pectinate line
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junction between the endodermal and ectodermal regions of the anal canal, found just below the anal columns, where the epithelium changes from columnar to stratified squamous
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hemorrhoids
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found in the portion of the anal canal from the protoderm (ectoderm)
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Hirschsprung disease (aganglionic megacolon)
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a failure of migration of neural crest cells into the developing gut tube, usually affects the sigmoid colon and results in a section of the gut tube which is lacking ganglia and unableto contract
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imperforate anus
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when the anus does not have contact with the rectum
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rectovaginal fistula (rectovesicle in male)
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when the rectum has a communication point with the vagina (or bladder in males), caused by incomplete separation of the hindgut from the urogenital sinus by the urorectal septum, may also arise if the cloaca is too small causing the opening of the hindgut to shift anteriorly
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rectoperineal (rectoanal atresia) fistula
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when the rectum terminates into the perineal body, result from vascular accidents involving the caudal region of the hindgut, resulting in atresias and fistulas
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urinary system
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originates from intermediate mesoderm, composed of 3 kidneys in succession cephalically to caudally (pronephraos, mesonephros, metanephros)
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pronephros
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found in the cervical region, nonfunctional and exists only at week 4
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mesonephros
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thoracolumbar, appear at 4th week and disappear by the end of the 2nd month except for mesonephric duct in males, originates from intermediate mesoderm
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characteristics of the mesonephros at week 4
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during the 4th week the first excretory tubules are formed, they lengthen and acquire a tuft of capillaries that will form glomerulus, Bowman’s corpuscle form around the glomerulus forming a renal corpuscle, laterally the tubules enter the collecting duct called a mesonephric (Wolffian) duct
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characteristics of the mesonephros at the 2nd month
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urogenital ridge = future gonads
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metanephros
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appear at the 5th week, definitive kidney, ureteric bud outgrown from the mesonephric duct penetrate metanephric tissue and induces metanephric blastema (from intermediate mesoderm)
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collecting system
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ureteric bud continues to divide, forms ureters, renal pelvis, major and minor calyces and collecting tubules
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filtration (excretory) system
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formed by metanephric mesoderm induced by the ureteric bud, metanephric tissue cap (cover the distal end of the collecting tubule) induces the formation of small renal vesicles, these give rise to S-shaped tubules, capillaries grow and become glomeruli
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Nephron
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the excretory unit, composed of glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle and distal convoluted tubule
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molecular signals responsible for kidney development
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kidney development is dependent upon epithelial mesenchymal interactions
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WT1 gene and kidney development
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expressed in mesenchyme, maintaining its competency to the induction by the ureteric bud
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glial-derived neurotrophic factor (GDNF) and hepatocyte growth factor (HGF) and kidney development
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expressed in mesenchyme, stimulate branching and growth of the ureteric buds
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RET and MET and kidney development
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recetpros for GDNF and HGF respectively, expressed in the epithelium of the ureteric bud
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PAX2 and WNT4 and kidney development
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responsible for conversion of the mesenchyme into an epithelium
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autosomal recessive polycystic kidney disease
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cyst formation from collecting tubules, renal failure in infancy or childhood
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autosomal dominant polycystic kidney disease
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cyst formation from all segments of the nephron, no renal failure until adulthood
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duplication of the ureter
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caused by early splitting of the ureteric bud, partial or complete splitting are possible, ectopic ureter opening (vagina, urethra or vestibule)
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ascent of the kidneys
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pelvic position -> upper position: caused by the decreasing body curvature and by the growth of the body in the lumbar and sacral regions, the mesonephric system degenerates almost entirely; some remnants in contact with the gonad, in both sexes gonads descend from their original level to a much lower position
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positioning defects of the kidney
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kidneys form in pelvis, if kidneys fuse can lead to horseshoe kidney stuck inferior to the IMA
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bladder formation
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cloaca divides into UG sinus (anterior) and the anal canal (posterior) by urorectal septum
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UG sinus
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upper: largest, bladder (initially connected with allantois, later urachus connects bladder and umbilicus, known as median umbilical ligament in adult)
pelvic part of the sinus: prostatic and membranous parts of the urethra lower phallic part: differ between the two sexes |
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development of the UG sinus into the urinary bladder and the definitive sinus
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mesonephric ducts are absorbed into the bladder wall -> ureter (initially outgrowth from it) enter the bladder separately -> ureteres move farther cranially, mesonephric ducts move lower to enter urethra where prostate forms, and ducts become ejaculatory ducts in males, part of ducts incorporated in bladder forms trigone area of the bladder
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formation of the trigone area of the bladder
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both mesonephric ducts and ureters originate from the mesoderm, the mucosa of the bladder formed by incorporation of the ducts, therefore is also mesodermal, with time the mesodermal lining of the trigone is replaced by endodermal epithelium
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urachal fistula
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bladder connected to umbilicus by urachus (old allantois, median umbilical ligament), if allantois persists, urachal fistula forms, a urachal cyst can form (a local area of allantois persists leading to cystic dilation), a urachal sinus can form when the upper part persists leading to the urine to drain from the umbilicus
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exstrophy of the bladder
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a ventral body wall defect (the bladder mucosa is exposed), epispadias is a constant feature, a lack of mesodermal migration into the region between the umbilicus and genital tubercle, followed by rupture of the thin layer of ectoderm
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epispadias
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a malformation in which the urethra opens on the dorsum of the penis, frequently associated with exstrophy of the bladder
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sex determination
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at fertilization (presence or absence of the Y chromosome), male/female morphology does not develop until the 7th week
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genital (gonadal) ridges
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derived from proliferation of epithelium and condensation of underlying mesenchym, germ cells appear at the 6th week
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primordial germ cell (PGC) migration pathway
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endodermal cells in the wall of the yolk sac close to allantois, they migrate by ameboid movement along the dorsal mesentery of the hindgut and arrive at the primitive gonads at the beginning of the 5th week, they invade the gonadal ridges in the 6th week and begin to develop, once PGCs arrive, epithelium of the genital ridge proliferates and penetrate the underlying mesenchyme
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PGCs role
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induce the development of the testis or ovary, no PGCs no testes/ovaries, carry the Y chromosome
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primitive sex cords
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indifferent gonads
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testis formation
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PGCs carry Y chromosome and induce release of SRY (TDF), this causes the primitive sex cords to become testis/medullary cords and these converge at the rete testis and are covered by tunica albuginea
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tesits cords during the 4th month of development
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are composed of PGCs and Sertoli cells (derived from the surface epithelium, somatic cell component)
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further testis cord development
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remain solid until puberty where they undergo canalization, seminiferous tubules joined at the rete testis, connected to the ductuli efferentes (remaining part of the excretory tubules of the mesonephric system), these are linked to the mesonephric duct (which becomes the ductus deferens)
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interstitial Leydig cells
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derived from the original mesenchyme of the gonadal ridges, lie between testis cords
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when does testosterone production begin
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8th week in the interstitial Leydig cells, testosterone is important for the development of the genital ducts and external genitalia
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ovary formation
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PGCs carry no Y chromosome, the sex cords thus dissociate into irregular cell clusters causing degeneration of the medullary cords, cortical cord develop from surface epithelium penetrating the underlying mesenchyme, the cords split into cell clusters surrounding the PGCs, PGCs become oogonia and surrounding cells become follicular cells
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features of sexual development
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at the beginning of human development either male or female development is possible, unspecialized gonads and two sets of reproductive ducts exist until week 6, an embryo develops as a male or female using information from the Y chromosome
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role of SRY
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it activates a cascade of developmental events, SRY tells the testis to make interstitial cells and sustentacular cells (sustenticular cells release anti-Mullerian hormone that tell the mullerian ducts (female rudiments to degenerate), tells cholesterol to turn into testosterone
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role of testosterone in male development
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can pass through the cell membrane bind to receptors and stimulate development of the internal male structures (epididymis, vas deferens, seminal vesicles, ejaculatory ducts), can also be stimulated by SRY to make DHT which stimulates external male structures (urethra, prostate, penis and scrotum)
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molecular pathway for sex determination in males
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1. genital ridge + SF1 + WT1 + LHX9 -> biopotential gonad
2. biopotential gonad + SRY + SOX 9 -> testis -> leydig cells 3. leydig cells release SF1 which causes the release of testosterone |
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molecular pathway for sex determination in females
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1. genital ridge + SF1 + WT1 + LHX9 -> biopotential gonad
2. biopotential gonad + DAX1 + WNT4 -> ovary -> follicles 3. follicles release estrogen which tells the Mullerian ducts to create female internal genitalia (uterus, oviduct, cervix, upper vagina) |
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genital ducts in the male
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excretory tubules remain while the mesonephros regresses, some become epigenital tubules in contact with the rete testis, become efferent ductules (caudal portion to the testis), paragenital tubules, paradidymis, mesonephric ducts elongate and become the epididymis, leads to the ductus deferens (vas deferens) to the seminal vesicle and then to the ejaculatory duct
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genital ducts in the female
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mesonephric (Wolffian) ducts + paramesonephric (Mullerian) ducts exist in both sexes in the earlier development, female genital ducts develop from the paramesonephric ducts, the mesonephric duct regresses creating the remnants epoophoran and paroophron
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paramesonephric (Mullerian) ducts
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derived from genital ridges, cranial end opens to abdominal cavity and caudal end grow and fuse with another one, becomes the uterine canal and goes to the paramesonephric tubercle in females, degenerates in males
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Gartner’s cyst
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a small caudal portion of the mesonephric duct remnants in the wall of the uterus or vagina
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broad ligament of the uterus
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divides the pelvic cavity into uterorectal and uterovesical pouches, fused part becomes the corpus and cervix of the uterus, mesenchyme becomes myometrium
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formation of the vagina
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vagina has a dual origin, upper portion from the uterine canal (from paramesonephric duct), lower portion from the urogenital sinus
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formation of the hymen
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epithelial lining of the sinus and a thin layer of vaginal cells, it is frequently absent (even in virgins) although remnants are commonly present as hymenal caruncula tags
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uterus didelphys
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double uterus
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uterus arcuatus
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slightly indented in the middle
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uterus bicornis
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two uterine horns entering a common vagina (common in many mammals below primates)
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external genitalia
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in the 3rd week mesenchyme cells from primitive streak migrate around the cloacal membrane, create cloacal folds, cranial portions unite creating the genital tubercle (anterior portion), urethral folds (posterior portion), anal folds, genital swelling (scrotal swelling in the male and labia majora in the female
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external genitalia in the male
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genital tubercle: penis
urethral folds: fuse=urethra genital swelling: fuse=scrotum development of male external genitalia depends on androgen produced by the fetal testis (Leydig cells), rapid elongation of the genital tubercle leads to phallus, phallus pulls the urethral fold forward forming the urethral groove, lined with epithelium from the endoderm, forms the urethral plate, at the end of the 3rd month the two urethral folds close over the plate forming the penile urethra, solid epithelial cord canalizes to form lumen and the urethral outlet of the gland penis |
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external genitalia in the female
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genital tubercle: clitoris
urethral folds: no fusion=labia minor genital swelling: no fusion=labia majora estrogen stimulates the development of the female external genitalia, genital tubercle slightly elongates forming the clitoris, urethral folds do not fold and become the labia minora, genital swelling occurs at the labia majora, genital tubercle is larger in the female than in the male between 3rd-4th month (not reliable for sex id) |
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hypospadias
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incomplete fusion of the urethral folds leading to abnormal openings of the urethra along the inferior aspect of the penis, openings can occur near the gland > shaft > base, incidence of about 3/5/1,000, doubling over the past 20 years, environmental estrogen may be the cause
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epispadias
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a malformation in which the urethra opens in the dorsum of the penis, occurs as an isolate defect but reguently associated with the exstrophy of the bladder, a lack of mesodermal migration into the region between the umbilicus and the genital tubercle followed by rupture of the thin layer of ectoderm
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micropenis
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2.5 standard deviations below average size fro the age group, insufficient androgen stimulation caused by hypogonadonism or hypothalamic or pituitary dysfunction
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bifid penis/double penis
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genital tubercle splits
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pseudohermaphroditis
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female has 46 chromosomes, XX, ovaries, uterus, usually caused by congential adrenal hyperplasia (AKA adrenogenital syndrome), excessive production of androgens leads to masculinization of the external genitalia, enlargement of the clitoris to almost male genitalia, partial fusion of the labia majora resembling scrotum
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androgen insensitivity syndrome (testicular feminization)
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46 chromosomes, XY, but tissue unresponsibe to testosterone due to androgen receptor mutations, dihydrotestosterone drives external genitalia development, testes present (inguinal or labial region), cryptorchidism (1/3 chanec to develop malignancy before age 50), MIS paramesonephric system is suppressed, no uterine tubes and uterus formation, vagina is short and blind, no testosterone + estrogen = female, X-linked recessive, incidence:1/20,000 live births
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descent of the testes
|
develop in abdomen, descend to scrotum through internal ring (inguinal canal), and external ring proceeded by vaginal process that later surrounds each testis as the tunica vaginalis, gubernaculum attaches to caudal pole and to scrotum = assists in descent
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cryptorchidism
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one or both testes do not desend
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inguinal hernia (indirect)
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vaginal processus fails to close and intestines pass through rings to scrotum
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hydrocele
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cysts secreting fluid
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CNS
|
first appears at the beginning of the 3rd week, a slipper shaped plate of thickened ectoderm (the neural plate in front of the primitive node, lateral edges elevate to form the neural folds, meet and form the neural tube)
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neural tube fusion
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begins in the cervical region and proceeds in cephalic and caudal directions, have open ends called the cranial and caudal neuropores that allow for communication with the amniotic cavity, final closure of the cranial neuropore occurs at the 18-20 somite stage (25th day), closure of the caudal portion occurs 2 days later
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dilations of the cephalic end of the neural tube
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1. primary brain vesicles-prosencephalon (forebrain)
2. mesencephalon (midbrain) 3. rhombencephalon (hindbrain) |
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flexures of the cephalic end of the neural tube
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1. cervical flexure-at the junction of the hindbrain and the spinal cord
2. cephalic flexure-in the midbrain region |
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prosencephalon
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primary brain vesicle, at 5 weeks consists of the telencephalon (formed by a midportion and two lateral outpocketings, the primitive cerebral hemispheres) and the diencephalon (characterized by outgrowth of the optic vesicles, marked by a cavity the third ventricle)
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rhombencephalic isthmus
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separates the mesencephalon from the rhombencephalon
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rhombencephalon
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consists of two parts, the metencephalon (which later forms the pons and cerebellum) and the myelencephalon, rhombencephalon marked by a cavity the fourth ventricle
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pontine flexure
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the boundary found between the metencephalon and the myelencephalon
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central canal
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lumen of the spinal cord, is continuous with that of the brain vesicles
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lateral ventricles
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cavities of the cerebral hemisphere
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aqueduct of Sylvius
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lumen of the mesencephalon connects the third and fourth ventricles, becomes very narrow
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interventricular foramina of Monro
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allows for communication between the lateral ventricle and the third ventricle
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neuroepithelial cells
|
in spinal cord formation, cells found on the wall of a recently closed neural tube, extend over the entire thickness of the wall and form a thick pseudostratified epithelium, connected by junctional complexes, dividing cells found on the lumen layer, this layer constitutes the neuroepithelial layer or neuroepithelium
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neuroblasts
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in spinal cord formation, arise from neuroepithelial cells after neural tube closure, have large round nucleus with pale nucleoplasm, near the basement membrane layer, form the mantle layer, primitive nerve cells, do not have the ability to divide
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mantle layer
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zone around the neuroepithelial layer, later forms the gray matter of the spinal cord
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marginal layer
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outermost layer of the spinal cord, contains nerve fibers emerging from neuroblasts in the mantle layer, forms the white matter of the spinal cord
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layers of the spinal cord
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from inside out, lumen -> neuroepithelial layer -> mantle layer (consists of neuroblasts) -> marginal layer
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basal plate
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ventral thickening due to continuous addition of neuroblasts to mantle layer, contains the ventral motor horn cells, form the motor areas of the spinal cord
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alar plates
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dorsal thickening that forms the sensory areas
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sulcus limitans
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a longitudinal groove that separates the basal and alar plates
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roof plate
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the dorsal midline portion of the neural tube, does not contain neuroblasts, serve as pathways for nerve fibers crossing from one side to another
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floor plate
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the ventral midline portion of the nueral tube, does not contain neuroblasts, serve as pathways for nerve fibers crossing from one side to another
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intermediate horn
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between the ventral and dorsal horn, contains neurons of the sympathetic portion of the autonomic nervous system, present only in thoracic and upper lumbar levels of the spinal cord (T1-L2or3)
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differentiation of the neuroblasts
|
initially have a central process extending to the lumen (transient dendrite) but when they migrate into the mantle layer, this process disappears and the nueroblasts are temporarily round and called apolar neuroblasts, differentiates into a bipolar neuroblast with two new cytoplasmic process on opposite sides of the cell body, differentiates into a multipolar neuroblast (and finally into a neuron)
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ventral motor root of the spinal nerve
|
occur when the axons of neurons in the basal plate break through the marginal zone and become visible on the ventral aspect of the cord, conduct motor impulses from the spinal cord to the muscles, also give rise to fibers of the dorsal root ganglion
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spinal nerve
|
formed from dorsal sensory root and ventral motor root
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association neurons
|
formed from dorsal sensory roots that break into the alar plate and ascend to higher or lower levels to form association neurons
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gliablasts
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primitive supporting cells, formed by neuroepithelial cells after production of neuroblasts ceases, migrate to the mantle and marginal layers, in the mantle layer differentiate into protoplasmic astrocytes and fibrillar astrocytes
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oligodendroglial cells
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may differentiate from the gliablasts or from mesenchyme, found primarily in the marginal layer, forms myelin sheaths around the ascending and descending axons in the marginal layer
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microglial cell
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appears in the 2nd half of development, appears in the CNS, highly phagocytic, derived from mesenchyme
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ependymal cells
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produced from neuroepithelial cells after formation of gliablasts, line the central canal of the spinal cord
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neural crest cells
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appear during elevation of the neural plate, ectodermal in origin, migrate laterally and give rise to sensory ganglia (DRG), neuroblasts here form two processes, centrally growing ones penetrate the dorsal portion of the neural tube, enter the spinal cord and become dorsal sensory root of the spinal nerve, peripherally growting ones join fibers of the ventral motor roots and form the trunk of the spinal nerve, terminate in the sensory receptor organs
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other things the neural crest cells form
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sympathetic neuroblasts, Schwann cells, pigment cells, odontoblasts, meninges, and mesenchyme of the pharyngeal arches
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ventral nerve roots
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an accumulation of motor nerve fibers from the basal plate
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dorsal nerve roots
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an accumulation of fibers originating from cells in the DRG
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spinal nerve
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formed from the distal processes of the ventral and dorsal nerve roots, split almost immediatlye to form dorsal and ventral primary rami
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dorsal primary rami
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innervate dorsal axial musculature, vertebral joints and the skin of the back
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ventral primary rami
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innervate the limbs and ventral body wall and form the major nerve plexuses (brachial and lumbosacral)
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Schwann cells
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myelinate the peripheral nerves, originate from neural crest, migrate peripherally and wrap themselves around axons forming the neurilemma sheath, myelin normally around many nerve fibers by the 4th month
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oligodendroglial cells
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myelinate nerves in the spinal cord (CNS), begins in approx. the 4th month of intrauterine life but may not happen until the first year of life, become myelinated by the time they start to function
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positional changes of the cord
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in the 3rd month of development, spinal nerves pass through the IV foramina at their level of origin, as we age, the vertebral column and dura lengthen faster than the neural tube, at birth the spinal cord is at the L3 level, dura remains attached to the coccygeal level
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adult positioning of the cord
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ends at about L2 or L3, dural sac and suarachnoid space at S2
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filum terminale
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thin extension of the pia mater, marks the tract of regression of the spinal cord
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cauda equina
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nerve fibers below the terminal end of the cord
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spina bifida
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neural tube defects (NTDs) that affect the spinal region, consists of splitting of the vertebral arches and may or may not involve underlying neural tissue
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spina bifida occulta
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defect in the vertebral arches covered by skin, usually does not involve underlying tissue, associated with hair over the region affected, occurs in the lumbosacral region, defect due to a lack of fusion of the vertebral arches
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spina bifida cystica
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severe NTD, neural tissues and/or meninges proture through a defect in the vertebral arches and skin to form a cystlike sac, usually not associated with mental retardation though, usually only fluid filled meninges protrude trough the defect
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meningocele
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occurs when only fluid-filled meninges herniated through the defect
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meningomyelocele
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occurs when meninges and neural tissue herniated through the defect
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myeloschisis (rachischisis)
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occurs when the neural folds do not elevate but remain as a flatted mass of neural tissue
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hydrocephaly
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develops in virtually every case of spina bifida cystica, spinal cord is tethered to the vertebral colum pulling the cerebellum into the foramen magnum cutting off the flow of CSF
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basal and alar plates and brain formation
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represent motor and sensory areas respectively, found on each side of the midline in the rhombecephalon and mesencephalon, in the prosencephalon, the alar plates are accentuated and the basal plates regress
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parts of the rhombencephalon (hindbrain)
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consists of the myelencephalon (most caudal of the brain vesicles) and the metencephalon (extends from the pontine flexure ot the rhombencephalic isthmus
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myencephalon
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gives rise to the medulla oblongata, its lateral walls are everted
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motor nuclei of the basal plate of the myelencephalon
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separated into three groups, a medial somatic efferent group, an intermediate special visceral efferent group and a lateral general visceral efferent group
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medial somatic efferent group of myencephalon
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continas motor neurons which form the cephalic continuation of the anterior horn cells, continues restrally into the mesencephalon, includes neurons of the hypoglassal nerve that supply the tongue, neurons of the abducens, trochlear and occulomotor nerves supplying the eye musculature
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special visceral efferent group of myencephalon
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f\extends into the metencephalon, forming the special visceral efferent motor column, motor neurons supply striated muscles of the pharyngeal arches, in the myencephalon the column is represented by neurons of the accessory, vagus, and glossopharyngeal nerves
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general visceral efferent group of myencephalon
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contains motor neurons that supply involuntary musculature of the respiratory tract, intestinal tract and heart
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gropus of the alar plate in the myelencephalon
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contain three groups of sensory relaty nuclei, lateral somatic afferent (sensory) group, intermediate special visceral afferent group, and the medial general visceral afferent group
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somatic afferent sensory group of myencephalon
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receives impulses from the ear and surface of the head by way of the vestibulocochlear and trigeminal nerves
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special visceral afferent of myencephalon
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group receives impulses from taste buds of the tongue and from the palate, oropharynx and epiglottis
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general visceral afferent of myencephalon
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group receives interoceptive information from the gastrointestinal tract and heart
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roof plate of myelencephalon
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consists of a single layer of ependymal cells covered by the pia mater forming the tela choroidea
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choroid plexus
|
produces CSF
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metencephalon
|
characterized by basal and alar plates, forms two compartments: the cerebellum and the pons
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cerebellum
|
a coordination center for posture and movement
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pons
|
the pathway for nerve fibers between the spinal cord and the cerebral and cerebellar cortices, arises from the marginal layer of the basal plates of the metencephalon, expands and makes a bridge for nerve fibers
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pontine nuclei
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found in the pons, originate in the alar plates of the metencephalon and myelecephalon
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basal plate of the metencephalon
|
three groups of motor neurons, the medial somatic efferent group, the special visceral efferent gtoup and the general visceral efferent group
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somatic efferent group of the metencephalon
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gives rise to the nucleus of the abducens nerve
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special visceral afferent group of the metencephalon
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containing nuclei of the trigeminal and facial nerve which innervate the musculature of the first and second pharyngeal arches
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general visceral efferent group of the metencephalon
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axons supply the submandibular and sublingual glands
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alar plates of the metencephalon
|
contain three groups of sensory nuclei: the lateral somatic afferent group, the special visceral afferent gropu and the general visceral afferent group
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somatic afferent group of the metencephalon
|
contains neurons of the trigeminal nerve and a small portion of the vestibulocochlear complex
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rhombic lips
|
formed from the dorsolateral parts of the alar plates when they bend medially, further deepening of the pontine flexure cause the rhombic lips to compress cephalocaudally and form the cerebellar plate (composed of a midline plate, vermis, and two lateral portion, hemispheres)
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flocculonodular lobe
|
is phylogenetically the most primitive part of the cerebellum
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cerebellar plate
|
initially consists of neuroepithelial, mantle and marginal layers, during further development, neuroepithelium migrate to the surface of the cerebellum to form the external granular layer
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external granular layer
|
cells of this layer retain their ability to divide and form a proliferative zone on the surface of the cerebellum, in the 6th month of development this layer gives rise to cells that migrate toward the Purkinje cells and give rise to granule cells
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basket and stellate cells
|
produced by proliferating cells in the cerebellar white matter
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cortex of the cerebellum
|
consists of the Purkinje cells, Golgi II neurons and neurons produced by the external granular layer, reaches its definitive size after birth
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dentate nucleus
|
deep cerebellar nuclei that reaches their final position before birth
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basal plate in the mesencephalon (midbrain)
|
each basal plate contains two groups of motor nuclei: a medial somatic efferent group and a small general visceral efferent gropu
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medial somatic efferent gropu of the mesencephalon
|
represented by the oculomotor and troclear nerves, innervate the eye musculature
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small general visceral efferent gropu of the mesencephalon
|
represented by the nucleus of Edinger-Westphal, innervates the sphincter pupillary muscle
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marginal layer of the basal plate of the mesencephalon
|
enlarges and forms the crus cerebri, serve as pathways for nerve fibers desending from the cerebral cortex to lower centers in the pons and spinal cord
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alar plates in the mesencephalon
|
initially appear as two longitudinal elevations separated by a shallow midline depression, a transverse groove divides each elevation into an anterior (superior) and posterior (inferior) colliculus, colliculi are formed by waves of neuroblasts migrating into the marginal zone
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posterior colliculi of the mesencephalon
|
serve as synaptic relay stations for auditory reflexes
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anterior colliculi of the mesencephalon
|
function as crrelation and reflex centers for visual impulses
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prosencephalon (forebrain)
|
consists of the telencephalon (which forms the cerebral hemispheres) and the diencephalon (which forms the optic cup and stalk, pituitary, thalamus, hypothalamus and epiphysis
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diencephalon
|
though to consist of a roof plate and two alar plates but lack floor and basal plates
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roof plate of the diencphalon
|
consists of a single layer of ependymal cells covered by vascular mesenchyme (gives rise to the choroid plexus of the third ventricle)
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epiphysis (pineal body)
|
arises from the most caudal part of the roof plate, initially appears as an epithelial thickening but begins to evaginate, eventually becomes a solid organ on the roof of the mesencephalon that serves as a channel through which light and darkness affect endocrine and behavioral rhythms, calcium is freq. deposited here and serves as a landmark on radiographs
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alar plate of the diencephalon
|
forms the lateral walls of the diencephalon
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hypothalamic sulcus
|
divides the plate into a dorsal and a ventral region, the thalamus and hypothalamus, respectively
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thalamus
|
gradually projects into the lumen of the diencephalon, fuse at midline and form the massa intermedia (interthalamic connexus)
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hypothalamus
|
forms the lower portion of the alar plate, differentiates into a number of nuclear areas that regulate the visceral functions, including sleep, digestion, body temperature and emotional behavior
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mamillary body
|
forms a distinct protuberance on the ventral surface of the hypothalamus on each side of the midline
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hypophysis (pituitary gland)
|
develops from two completely different parts: an ectodermal outpocketing of the stomodeum in front of the buccopharyngeal membrane (Rathke’s pouch) and a downward extension of the diencphalon (infundibulum)
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anterior lobe of the hypophysis (adenohypophysis)
|
formed from cells in the anterior wall of Rathke’s pouch, has a small extension (pars tuberalis) that grow along the stalk of the infundibulum and surrounds it
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pars intermedia
|
formed from the posterior wall of Rathke’s pouch, seems to have little significance in humans
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parts of the infundibulum
|
gives rise to the stalk and the pars nervosa (posterior lobe of they hypophysis, neurohypophysis) it is composed of neuroglical cells, also contains a number of nerve fibers from the hypothalamic area
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pharyngeal hypophysis
|
occurs when a small protion of Rathke’s pouch persists in the roof of the pharynx
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|
craniopharyngiomas
|
occur from remnants of Rathk’s pouch, they may form within the sella turcica or along the stalk of the pituitary but usually lie above the sella, may cause hydrocephalus and pituitary dysfunction (diabetes insipidus or growth failure)
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telencephalon
|
most rostral part of the brain vesicels, consists of two lateral outpocketings: the cerebral hemispheres and a median portion (lamina terminals)
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lateral ventricles
|
the cavities of the hemispheres, communicate with the lumen of the diencephalon through the interventricular foramina of Monro
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|
cerebral hemispheres
|
arise at the beginning of the 5th week, are bilateral evaginations of the lateral wall of the prosencephalon
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hippocampus
|
fromed from a wall thickening of the hemisphere above the choroidal fissure (where the choroid plexus protrudes into the lateral ventricle), primary function is olfaction, bulges into the lateral ventricle
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|
portions of the corpus striatum
|
a dorsomedial portion (caudat nucleus) and a ventrolateral portion (the lentiform nucleus)
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internal capsule
|
separates the caudate nucleus from the lentiform nucleus
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|
formation of brain lobes
|
occurs from continuous growth of the cerebral hemispheres in anterior, dorsal and inferior directions
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insula
|
depression that separates the frontal and temporal lobes, at birth this region is later overgrown by the adjacent lobes being completely covered
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gyri
|
convolutions in the brain that occur during the final part of fetal life, occurs because the surface of the cerebral hemispheres grow so rapidly, separated by fissures and sulci appear on its surface
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|
cerebral cortex
|
develops from the pallium, pallium has two regions: the paleopallium (archipallium) and the neopallium
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|
paleopallium
|
immediately lateral to the corpus striatum
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neopallium
|
between the hippocampus and the paleopallium, waves of neroblasts migrate to a subpial position and then differentiate into fully mature neuron, the next wave forms on top of it so the old layer is deepest
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pyramidal cells
|
cells that make up the motor cortex
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granular cells
|
cells that make up the sensory areas of the cortex
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|
olfactory system
|
dependent on epithelial-mesenchymal interaction, occur between neural crest cells and ectoderm to form the olfactory placodes and the neural crest cells and the floor of the telencephalon to form the olfactory bulbs
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|
nasal placode cells
|
differentiate into primary sensory neurons, axons grow and make contact with secondary neurons in the olfactory bulbs, olfactory bulbs and olfactory tracts from the olfactory nerve
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|
commissures
|
fiber bundles, corss the midline and connect the right and left halves of the hemispheres
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|
lamina terminalis
|
used as a commisure for the most important fiber bundles
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|
anterior commissure
|
first of the crossing bundles to appear, consists of fibers connecting the olfactory bulb and related brain areas of one hemisphere to those of the opposite side
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|
hippocampal (fornix) commissure
|
second commisure to appear, fibers arise in the hippocampus and converge on the lamina terminalis close to the roof plate of the diencephalon, the fibers continue forming an arching system to the mamillary body and the hypothalamus
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corpus callosum
|
the most important commissure, appears by the 10th week of development and connects the nonolfactory areas of the right and left cerebral cortex, arches over the thin rood of the diencephalon
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|
posterior and hanenular commissures
|
just below and rostral to the stalk of the pineal gland
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|
optic chiasma
|
appears in the restral wall of the diencephalon, contains fibers from the medial halves of the retinae
|
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|
holoprosencephaly (HPE)
|
refers to a spectrum of abnormalities in which a loss of midline structures results in malformations of the brain and face, caused by mutations in SHH
|
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|
telencephalic vesicle (alobar HPE)
|
occurs when the lateral ventricles merge into a single telecephalic vesicle, the eys fuse and there is a singl nasal changer along with other midline facial defects
|
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|
Smith-Lemli-Opitz syndrome
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due to defective cholesterol biosynthesis, have craniofacial and limb defects and 5% have HPE, due to abnormalities in 7-dehydrocholesterol reductase (used in making cholesterol), abnormalities due to abnormal SHH signaling since cholesterol is necessary for this
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schizencephaly
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large clefts occur in the cerebral hemispheres, sometimes causing a low of brain tissue, mutations in the homeobox gene EMX2 appear to account for some of these cases
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meningocele, meningoencephalocele and meningohydroencephalocele
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all caused by an ossification defect in the bones of the skull, most affected bone is the squamous part of the occipital bone
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meningocele
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only if meninges bulge through
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exencephaly
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characterized by failure of the cephalic part of the neural tube to close, this causes the vault of the skull to not form leaving the malformed brain exposed
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anencephaly
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an exencephaly that occurs and is also associated with a mass of necrotic neural tissue, occurs 4X more likely in females
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craniorachischisis
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caused when the closure defect of the neural tube extends caudally into the spinal cord
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hydrocephalus
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characterized by an abnormal accumulation of CSF within the ventricular system, due to an obstruction of the aqueduct of Sylvius, prevents CSF from the lateral and 3rd ventricle to reach the 4th ventricle and from there into the subarachnoid space wehre it would be resorbed, fluid accumulates in the lateral ventricles and presses on the brain and bones of the skull
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Arnold-Chiari malformation
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caudal displacement and herniation of cerebellar structures through the foramen magnum, occurs in virtually every case of spina bifida cystica and accompanied with hydrocephalus
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microcephaly
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describes a cranial vault that is smaller than normal, may be genetic or due to prenatal insults to teratogens, impaired mental development occurs in more than half of cases
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absence of the corpus callosum
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does not have much of a functional disturbance if partially or completely absent
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absence of the cerebellum
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may result in only a slight disturbance of coordination
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maternal alcohol abuse
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leading cause of mental retardation
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cranial nerves
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by the 4th week, nuclei for all 12 CNs are present, all except olfactory (I) and optic (II) nerves arise from the brainstem, and only oculomotor (III) arises from outside the region of the hindbrain
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rhombomeres
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occurs in the hindbrain where proliferation centers in the neuroepithelium establish eight of these, give rise to motor nuclei of CN IV, V, VI, VII, IX, X, XI, XII, directed by mesoderm collected into somitomeres beneath the overlying neuroepithelium
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motor neurons for CN
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within the brainstem
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sensory ganglia for CN
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outside of the brain, originate from ectodermal placodes and neural crest cells, include the nasal, otic and 4 epibranchial placodes represented by ectodermal thickenings dorsal to the pharyngeal (bronchial) arches
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epibranchial placodes
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contribute to ganglia for nerves of the pharyngeal arches (V, VII, IX, and X)
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parasympathetic (visceral efferent) ganglia
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derived from neural crest cells and their fibers are carried by CN III, VII, IX and X
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sympathetic trunk
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formed from neural crest cells of the thoracic region that migrate to each side of the spinal cord, neuroblasts migrate toward the cervical and lumbosacral regions extending the sympathetic trunks to their full length
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preaortic ganglia
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comes from some sympathetic neuroblasts that migrate in front of the aorta, include the celiac and mesenteric ganglia
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sympathetic organ plexuses
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other sympathetic cells migrate to the heart, lungs and GI tract
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visceroefferent column (intermediate horn) nerve fibers
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penetrate the ganglia of the trunks, some of these nerves synapse at the same levels in the sympathetic trunks or pass through the trunks to preaortic or collateral ganglia
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preganglionic fibers
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have a myelin sheath and stimulate the sympathetic ganglion cells, form the white communicating rami when the pass from spinal nerve to sympathetic ganglia
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postganglionic fibers
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axons of the sympathetic ganglion cells, have no myelin sheath, they either pass to other levels of the trunk or extend to the heart, lungs and intestinal tract
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gray communicating rami
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pass from the sympathetic trunk to spinal nerves and from there to peripheral blood vessels, hair, and sweat glands, are found at all levels of the spinal cord
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suprarenal gland
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develops from two compartments: a mesodermal portion which forms the cortex and an ectodermal portion which forms the medulla
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formation of the suprarenal gland
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starts during the 5th week, mesothelial cells between the root of the mesentery and the developing gonad begin to proliferate and penetrate the underlying mesenchyme, they then differentiate into large acidophilic organs (fetal cortex AKA primitive cortex), a 2nd wave of cells from the mesothelium penetrates the mesenchyme and surrounds the original acidophilic cell mass, form the definitive cortex
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fetal cortex of the suprarenal gland after birth
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regresses rapidly except for its outermost layer, differentiates into the reticular zone, neural crest cells invade its medial aspect giving rise to the medulla of the suprarenal gland, called chromaffin cells
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preganglionic parasympathetic fibers
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given rise from the neurons in the brainstem and the sacral region of the spinal cord
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how do fibers from the nuclei in the brainstem travel
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via the oculomotor (III), facial (VII), glossopharyngeal (IX) and vagus (X) nerves
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Hirchsprung disease (congential mesocolon)
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results from a failure of parasympathetic ganglia to form in the wall of part or all of the colon and rectum because the neural crest cells fail to migrate, due to mutations in the RET gene
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primordium of head and neck development
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placodes, somites/somitomeres, and pharyngeal arches, pouches and clefts
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mesenchyme for formation of the head region
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paraxial (somites) and lateral plate mesoderm, neural crest and ectodermal placodes
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lateral plate mesoderm
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forms the laryngeal cartilages and connective tissue in this region
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neural crest cells and head and neck development
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form midfacial and pharyngeal arch skeletal structures and tissues in these regions
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placodes
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are ectodermal thickenings that form structures for our special senses, three types from three different parts, olfactory placode, lens placode and otic placode
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nasal/olfactory placode
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induced by the adjacent olfactory bulb of the forebrain, forms the primary olfactory epithelium, the cells of smell grow into the olfactory bulb through the ethmoid bone
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nasal cavity
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developmental stages of nasal cavity include a period when it is continuous with the oral cavity, obvious need for things to work in the proper separation of cavities
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eye development and the lens placode
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outpocketing of the forebraine (diencephalic part) induces a thickening of the surface ectoderm which will form the lens placode or vesicle, forebrain outpocketing continues to grow and forms the optic cup which forms all the layers of the retina as well as the RPE and parts of the iris and ciliary body
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choroid fissure and the central artery
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optic cup continues to invaginate anteriorly and ventrally which results in the choroid fissure, choroid fissue allows mesenchyme to move into the stalk, creates blood vessels (hyaloid artery) and a spossible embryological pathology
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coloboma
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pathology mentioned in previous card, may occur if choroid fissure fails to close, normally this fissure closes during the 7th week, if it does not can form a cleft, usually found in the iris only (coloboma iridis) but can extend into the ciliary body, retina, choroid and optic nerve
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what does mesenchyme that invades the optic cup form?
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muscles of the iris and ciliary body, also forms the sclera and choroid
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cornea
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comes from surface ectoderm and the underlying infiltrating mesenchyme, not the lens placode or optic cup
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cyclopia, anopthalmia
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severe eye defects associated with malformations of the brain and cranial cavity
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cyclopia
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single eye, comprise a spectrum of defects in which the eyes are partially or completely fused, due to a loss of midline tissue, usually associated with cranial defects, can be caused by alcohol or mutations in SHH and cholesterol metabolism
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anopthalmia
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is absence of the eye, in some cases, histological analysis reveals some ocular tissue, the defect is usually accompanied by severe cranial abnormalities
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congenital cataracts
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are either genetically determined or caused by a case of rubella in the mother during the 4th-7th weeks, lens becomes opaque during intrauterine life
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otic placode and ear development
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forms the membranous labyrinth and the sensory neurons of CN VIII, inner ear, slow development of the inner ear is important because environmental defects are more common
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environmental role on ear defects
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rubella virus, affecting the embryo in the 7th or 8th week, may cause severe damage to the organ of Corti, poliomyelitis, erythroblastosis fetalis, diabetes, hypothyroidism and toxoplasmosis
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middle ear cavity development
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the middle ear cavity forms from the adjacent 1st pharyngeal pouch lined by endoderm, the middle ear ossicles, malleus, incus and stapes come from the mesenchyme of the 1st and 2nd arches which invade between the pouch and cleft
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external auditory canal development
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forms from the adjacent 1st pharyngeal cleft between the 1st and 2nd pharyngeal arches not seen in this diaphragm
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tympanic membrane
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comes from three sources
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auricle
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the auricle or pinna develops from auricular hillocks which are blocks of mesenchyme from the 1st and 2nd arches, defects of the auricle are common and should be clues to other more serious problems like most chromosomal anomalies
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preauricular appendages and pits
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skin tages and shallow depressions anterior to the ear, pits may indicate abnormal development of the auricular hillocks, whereas appendages may be due to accessory hillocks, associated with other malformations
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somites/somitomeres
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masses of mesoderm that form skeletal muscles, preotic somites form muscles of the eye, postotic somites form muscles of the tongue, forms the floor of the brain case
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pharyngeal arches
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masses of mesenchyme tissue that flank the developing gut appear around the 4th-5th week, each arch consists of a core of mesenchyme surrounded by surface ectoderm on the outside and endoderm on the inside, neural crest cells exist in the core to contribute to skeletal components of the face, give rise to formation of the neck and face
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pharyngeal arch derivatives
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muscle, bone or cartilage, skin from the overlying ectoderm, lining of the gut from the lining endoderm
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skeletal elements
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cartilage or bone forms from each pharyngeal arch, the maxillary process forms the maxilla, zygomatic bone and part of the temporal bone, notice that the first arch forms the upper and lower jaws
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1st pharyngeal arch derivatives
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maxillary process last 2 slides, mandibular process forms the mandible, malleus and incus
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2nd pharyngeal arch derivatives
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hyoid arch forms the lesser horn of hyoid bone, styloid process and stapes
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3rd pharyngeal arch derivatives
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the rest of the hyoid bone
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4th and 6th pharyngeal arch derivatives
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fuse to form the laryngeal cartilages (crichoid and thyoid cartilage)
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proper formation of the face
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proper formation of the face requires that the major prominences merge correctly, the key elements are the maxillary prominence and the medial and lateral nasal prominences, the philtrum of the upper lip, the incisor portion of the upper jaw and the triangular primary palate back to the incisive canal are formed by the growing together of the medial nasal prominences
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facial malformations
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anterior to the incisive canal involves the primary palate and upper lip, whereas posterior to the canal involves more of the hard palate formed by the palatine bones of the maxillary prominence and the nasal septum of the frontonasal prominence
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cleft lip and palate
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involves a failure of any of these prominences to grow properly and can express in many formes, is fairly common, more freq. in males, maternal age dependent, isolated cleft palate is less common, more freq. in females, not related to maternal age, all clefts seem to have a genetic and environmental component and their incidence varies among different populations, some clefts are accompanied by mental retardation usually the midline varieties
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incisive foramen
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considered the dividing landmark between the anterior and posterior cleft deformities, anterior to this include lateral cleft lip, cleft upper jaw and cleft between the primary and secondary palates (due to a partial or complete lack of fusion of the maxillary prominence with the medial nasal prominence on one or both sides), posterior to the foramen include cleft (secondary) plate and cleft uvula
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1st pharyngeal arch derived muscles
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muscles of mastication
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2nd pharyngeal arch derived muscles
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muscles of facial expression
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3rd pharyngeal arch derived muscles
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stylopharyngeus
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4th and 6th pharyngeal arch derived muscles
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muscles of the pharynx, larynx and palate
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sensory innervation
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the endoderm lining each pharyngeal arch is innervated by the nerve of that arch
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innervation of the nasal cavity and anterior portion of the palate
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maxillary division of trigeminal (V2)
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innervation of the tongue
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mandibular division of trigeminal (V3)
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innervation of the posterior portion of the palate
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facial nerve (VII)
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innervation of the pharyngeal cavity
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glossopharyngeal (IX) nerve
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innervation of the trachea
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vagus (X) nerve
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what happened to V1 (ophthalmic)?
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it enters the block of tissue superior to the maxillary process, the orbit, and is sensory to periorbital structures
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1st pharyngeal pouches
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middle ear auditory/Eustachian tube
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2nd pharyngeal pouches
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palatine tonsil
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3rd pharyngeal pouches
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inferior parathyroid glands
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4th pharyngeal pouches
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sukperior parthyroid glands
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5th pharyngeal pouches
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C cells of the thyroid gland
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thyroid gland development
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grows down from the foramen cecum of the tongue near the floor of the pharynx, the inferior parathyroid glands from the third pouch are dragged down by the migrating thymus
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aberrant thyroid tissue
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migration of the thyroid gland can leave duct cysts or thyroid tissue anywhere along the course, commonly found in the base of the tongue, just behind the foramen cecum, and is subject to the same diseases as the thyroid gland itself
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what nerves innervate the 3 types of primordial
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cranial nerves
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what cranial nerves innervate the placodes
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CN I, II, VIII
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what cranial nerves innervate the somites
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CN III, IV, VI, XII
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what cranial nerves innervate the branchial arches
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CN V, VII, IX, X
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primordium of olfactory CN (I)
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olfactory placode
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primordium of Optic CN (II)
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optic vesicle
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primordium of oculomotor CN (III)
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preotic somite
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primordium of trochlear CN (IV)
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preotic somite
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primordium of trigeminal CN (V)
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branchial arch 1
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primordium of abducens CN (VI)
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preotic somite
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primordium of facial CN (VII)
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branchial arch 2
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primordium of vestibulocochlear CN (VIII)
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otic placode
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primordium of glossopharyngeal (IX)
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branchial arch 3
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primordium of vagus CN (X)
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branchial arch 4 and 6
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primoardium of spinal accessory (XI)
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not known
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primordium of hypoglossal CN (XII)
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postotic somites
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cranial nerve components
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every cranial nerve is unique, potential components include:
-special somatosensory (vision, hearing and balance) -general somatosensory (Skin) -general viscerosensory (gut) -special viscerosensory (taste and small) -somatomotor (muscles from somites) -visceromotor (autonomic) -branchiomotor (muscles from branchial/pharyngeal arches) |
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craniofacial malformations
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1. aberrant thyroid tissue or duct cysts along the course of descent
2. ectopic thymic and parathyroid tissue are common 3. neural crest cell defects are associated with severe heart defects |
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ectopic thymic and parathyroid tissue
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these glandular tissues migrate and sometimes remnants of these tissues persist along the pathway, particularly true for thymic tissue which may remain in the neck and parathyroid tissue, while the inferior parathyroids are more variable in position than the superior ones and are sometimes found at the bifurcation of the common carotid artery
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neural crest cell defects
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are essential for formation of much of the craniofacial region, disruption of their development results in severe craniofacial malformations, since neural crest cells also contribute to the conotruncal endocardial cushion (separates the heart into pulmonary and aortic channels), may lead to heart defects
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