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59 Cards in this Set

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What is cell differentiation?
The result of cells expressing some genes and suppressing others within a common genome
What is the embryonic period?
The time from fertilization to the earliest (primordial) stages of organ development
What is the fetal period?
The time b/w the embryonic period and parturition, during which organs and begin to function
What is fertilization?
Union of a haploid oocyte and a haploid spermatozoon, producing a diploid zygote (a pleuripotent cell capable of developing into a new individual)
Where does fertilization technically end?
Ends with the initiation of zygote cell division (the start of cleavage)
What are the primary germ layers?
Ectoderm, mesoderm, and endoderm
What forms from the ectoderm?
Epidermis of skin, epithelium of the oral & nasal cavities, and the nervous system and sense organs
What forms from the mesoderm?
Muscle and CT, including bone, and components of the circulatory, urinary, and genital systems
What forms from the endoderm?
Mucosal epithelium and glands of respiratory and digestive systems
Where does the yolk sac originate from?
Hypoblast, which is a new layer of cells from the inner cell mass inside the trophoblast layer
What is the remaining inner cell mass called once the hypoblast separates?
Epiblast
What forms on the epiblast surface as ridges separated by a depression?
Primitive streak
Where does the lining of the digestive tube originate from?
Endoderm
Where does CT, muscle, and mesothelium originate from?
Splanchnic mesoderm
What does the simple tubular structure form?
Foregut, hindgut, and midgut
What is the major development change that occurs in the esophagus?
Increased length
What kind of muscle is in esophagus?
Primarily skeletal muscle in most species. Pigs have short smooth muscle segment near stomach. Horses & cats have smooth muscle at the caudal 1/3 part of esophagus.
How is the monogastric stomach formed?
First dorsal enlargement formed, followed by 2 rotations for positioning. First rotation along cranio-caudal axis positions dorsal enlargement on left side.
Second rotation about a dorso-ventral axis, anticlockwise, positions caudal end of stomach to the right and cranial (with respect of the midline) and cranial end of the stomach to the left
How does the ruminant stomach form?
Begins like the monogastric stomach with a first rotation positioning the fundus to the left. Fundus undergoes a marked craniodorsal enlargement leftwards forming the beginnings of the rumen.
Smaller caudoventral outpocketing forms reticulum. Swelling on lesser curvature of stomach forms the omasum.
When does the rumen start to form?
At the 6th week
When does the change in orientation and differential growth of each chamber of the ruminant stomach occur?
7th week
How does the ruminant stomach position itself?
Rumen shifts caudodorsally: dorsal & ventral sacs now in position on the left. Reticulum shifted to more cranioventral position. Omasum & abomasum pushed over the the right. Duodenal-abomasal junction folds on itself and directed dorsally.
When is the ruminant stomach at its final position and form?
14 weeks gestation
How big is the rumen at birth? (compared to other compartments)
Half the size of abomasum
At what age is the calve's rumen the same size as the abomasum?
At 8 weeks postnatal
At what age is the rumen twice the size of the abomasum?
12 weeks postnatal
When does the ruminant stomach reach adult proportions?
1.5 yrs old
What is the rate of growth of the rumen based on?
Roughage consumption
How does the monogastric intestinal tract develop?
Midgut grows rapidly & loop of gut herniates into the coelomic cavity of umbilical cord. Vitelline artery accompanies the loop of gut. The caudal limb develops a diverticulum (cecum).
Continued growth causes a double twist of the loop around the blood vessels. When returned into the abdomen, viscera is in normal position.
What does the vitelline artery become?
Cranial mesenteric artery
How does the ruminant intestinal tract form?
Begins organization much like monogastric. Additional changes in caudal limb of loop that becomes ascending colon. The ascending colon forms a secondary loop which coils to form the spiral colon.
How does the equine intestinal tract form?
A secondary loop also develops in the ascending colon. Tip of the secondary loop is displaced leftward and caudally. As the cecum enlarges and its apex grows cranioventrally and its base enlarges it draws the initial part of the ascending colon caudally & rightward together with the future right dorsal colon
How does the liver develop?
Forms as a ventral outgrowth, the hepatic diverticulum, from the foregut endoderm in the region of the future duodenum. It grows into the mesoderm of the septum transversum.
How do hepatocytes form?
Inductive effect of mesoderm of septum transversum causes differentiation of diverticulum into hepatocytes
What does the hepatic diverticulum give rise to?
The liver parenchyma (endodermal cells) and the gall bladder
What does the parenchyma of the liver branch into?
Branches to form canaliculi which drain into duct system: bile, hepatic, cystic and gall bladder
Where do liver sinusoids develop from?
From the mesoderm of the septum transversum and the vitelline and umbilical veins that course through the septum to enter the sinus venosus of the heart
Where does the pancrease develop from?
From ventral diverticulum (from hepatic diverticulum) and dorsal diverticulum (from duodenum)
What brings the two diverticuli together (where pancreas form)?
Differential growth and rotation of the stomach brings the two together
Which diverticulum gives rise to the left lobe of the pancreas and which gives rise to the right lobe of the pancreas?
Dorsal diverticulum gives rise to the left lobe. Ventral diverticulum gives rise to the right lobe
What lobe of the pancreas does the accessory pancreatic duct originate from? What about the pancreatic duct?
Left lobe = accessory pancreatic duct
Right lobe = pancreatic duct
Which animals only have the accessory pancreatic duct present?
Ox & pig
Which animal only has the pancreatic duct present?
Sheep
Where do the mesenteries develop from?
The splanchnopleure of the tubular embryo (dorsal and ventral mesogastrium)
How do the mesenteries form?
Dorsal mesogastrium becomes fan-shaped. Visceral attachment grows faster than body wall attachment.
Which mesogastrium forms the greater omentum, which attaches to the greater curvature of the stomach?
Dorsal mesogastrium
Where does spleen develop from?
Develops in greater omentum from blood vessel plexus (celiac artery)
Which mesenteries does the horse lose?
Loss of ascending mesocolon on left dorsal and ventral colon (free to move)
What is contained in the ventral mesogastrium? And what forms in it?
Contains developing liver. Forms coronary ligaments.
What does the ventral mesogastrium form?
Lesser omentum, which attaches lesser curvature of the stomach to the liver
What does the hindgut give rise to?
Descending colon and rectum
What is the terminal part of the primitive gut called? What does it consist of?
Cloaca: it receives digestive, urinary, and genital systems
Hindgut enters dorsal portion of cloaca through what?
Anorectal canal
Allantois enters the ventral portion of cloaca through what?
Urogenital sinus
What is the urorectal septum formed from?
Mesoderm of allantois and yolk sac
What is the cloacal membrane (covers ventral surface of cloaca) formed from?
Ectoderm and endoderm
What does the urorectal septum become?
It lengthens caudally and becomes perineal body; forms anal opening and opening for urogenital sinus, hence partitioning cloacal membrane
What forms the bladder?
Part of allantois and cranial portion of urogenital sinus
Connection of bladder to umbilicus forms _____?
Urachus