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89 Cards in this Set

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Where does the gut come from?
- yolk sac --> primitive gut tube --> endodermal lining and intraembryonic visceral mesoderm
What are the adult derivatives of the foregut?
1) thyroid
2) pharyngeal pouches
3) esophagus
4) stomach
5) liver
6) gallbladder
7) bile ducts
8) pancreas
9) upper duodenum
What are the adult derivatives of the midgut?
1) Lower Duodenum
2) Jejunum
3) Ileum
4) Appendix
5) Ascending Colon
6) Proximal 2/3 of the Transverse Colon
What are the adult derivatives of the hindgut?
1) distal 1/3 of the Transverse Colon
2) Descending Colon
3) Sigmoid Colon
4) Rectum
5) Upper Anal Canal
6) Urogenital derivatives
What is the blood supply for the foregut, midgut and hindgut?
- Foregut --> celiac trunk
- Midgut --> Superior Mesenteric Artery
- Hindgut --> Inferior Mesenteric Artery
What will from the digestive system?
- During the 4th week, the yolk sac becomes incorporated in the intraembryonic ceolem as the primitive gut tube
- This extends from the stomodeum (mouth) to the proctoduem (anus)
- THIS will form the digestive system
What are the 3 layers of this tube?
• Foregut
• Midgut
• Hindgut
What forms the lining?
• The endodermal lining of the yolk sac will form the epithelial lining of the gut
• Intraembryonic mesoderm is the same as the splanchnopleuric layer of the intraembryonic mesoderm
So where is the esophagus derived from, what is the classification of its endothelium, and where does it get its epithelial lining?
• Foregut
• Stratified squamous non-keratinized
• Gets its lining from the endoderm
What is the muscle type for the 3 parts of the esophagus?
• Top = striated – from the mesenchyme in the pharyngeal arches
• Middle = mixed
• Lower = smooth – from the splanchnopleuric mesoderm
Esophygeal Atresia
- a failure of the foregut to canalize
- results an interrupted esophagus, which results in obstructed swallowing; which in the fetus would give rise to polyhrdaminous
• This is usually associated with tracheoesophageal fistula (TEF) – in which there is a comm.. b/w the trachea and the esophagus; results in the baby choking when she swallows milk, b/c it goes down the trachea
• 87% of the time you have EA with distal TEF
Describe the formation process of the stomach
• During the 4th week, there is a fusiform dilation in the foregut which causes rotation of the stomach.
• Ventral Border: moves to the right and becomes the lesser curvature
• Dorsal Border : moves to the left and becomes the greater curvature
So what happens anatomically during the rotation of the stomach?
• The Left surface becomes the anterior surface (supplied by the L. Vagus N) and the right surface becomes the posterior surface (supplied by the R. Vagus N)
What about the mesenteries of the stomach? What happens to them?
• The dorsal mesogastrium forms the greater omentum (since the dorsal surface moved to the left, and formed the greater curvature)
• The ventral mesogastrium forms the lesser omentum (since the ventral surface moved to the right and formed the lesser curvature
How is the lesser sac formed? Where is it, and how does it communicate with the greater sac?
• The rotation of the dorsal mesogastrium to the left is what creates the space behind the stomach known as the lesser sac
• Everything else is the greater sac
• The 2 sac communicate through the epiploic foramen
- So…if you go into the epiploic foramen, you will go into the lesser sac
Hypertrophic Pyloric Stenosis
• Congenital hypertrophy of part of the pylorus
• Infant will present with non-bilous, PROJECTILE vomiting
• EXORCIST BABY
Where does the duodenum develop from and what is it supplied by? What is the significance of the junction b/w these 2 segments?
• Caudal part – comes from the foregut
• Cranial Part – comes from the midgut
• Supplied by the celiac trunk and the superior mesenteric artery
• At the junction is the point at which the common bile duct opens into the duodenum
what is duodenal atresia associated with?
• Polyhydraminous
• Down’s Syndrome
Describe the formation of the liver
• Around the 4th week, there is a ventral outgrowth on the caudal part of the foregut, towards the septum transversum. This is called the liver bud/hepatic diverticulum
• The cranial end (larger) forms the Liver Primordium
• The caudal end (smaller) forms the gallbladder, cystic duct, and the common hepatic duct
Remember? The cystic duct and the common hepatic duct join to form the common bile duct
OR
The cystic duct and the common bile duct join the form the common hepatic duct
Name the various components of the liver and how they are formed.
• Epithelium of the liver is formed from the endoderm; foregut
• The mesoderm of the septum transversum forms the sinusoids and the Kupffer cells
• The ventral mesentery Ant. To the liver forms: Falciform Ligament
Post. To the Liver: lesser omentum
• When you think of the liver, think of rows of hepatocytes, which come from the liver bud, which is from the foregut, which is ENDODERMAL in origin
• On either sides of these rows will be sinusoids, which will be carrying blood: anything assoc. with blood will come from the mesoderm!! So these come from the mesoderm of the septum transversum
• Also, there will be Kupffer cells, which are macrophages! Macrophages come from monocytes, which come from the mesoderm, so Kupffer cells are from the mesoderm of the septum transversum as well
When does Hemopoeisis in the liver begin?
• At the 6th week
Name the order in which blood production occurs in the body
• 1st produced in the yolk sac
• 2nd in the spleen and liver
• 3rd in the bone marrow (this is what adults have)
Note: in some leukemias where there is a massive production of RBC’s the liver and spleen may start to help with hemopoeisis again. When this happens, the liver and spleen will enlarge!!
What is meconium, and why is it green?
• The first stool of the infant
• The bile is produced by the liver, then concentrated and stored in the gallbladder, and then secreted by the cystic duct and the common hepatic duct, which goes down the common bile duct to the duodenum, where it stains the stool green
From where does the gallbladder from?
• The hepatic diverticulum
When does the flow of bile begin?
• 12th week
From what and how does the pancreas form?
• It forms from ventral and dorsal pancreatic buds
• The ventral bud migrates dorsally, and ultimately lies inferior to the dorsal bud (this is why the CBD is posterior to the duodenum
• The 2 buds ultimately fuse
What are the different parts of the pancreas, and where are they formed from?
• Head of the pancreas, and the uncinate process – ventral pancreatic duct
• Remaining part of the hesd, and the body and tail – dorsal pancreatic duct
• Main pancreatic duct – entire part of the ventral pancreatic duct, and the distal part of the dorsal pancreatic duct
• Islets of Langerhans – endoderm
• Accesory Pancreatic Duct – part of the dorsal pancreatic duct
Annular Pancreas
• Results from the lack of rotation of the pancreas, causes the pancreas to be curving over and around the duodenum
• This is usually asymptomatic, but in some cases, it can cause the classical vomiting symptom
• Can be easily corrected with surgery
NOTE:
• Nothing in the GIT has contributions from the Ectoderm!! Endoderm ONLY
How does the spleen form?
• The accumulation of the dorsal mesogastium forms the spleen
• As the stomach rotates (around the 4th week remember) the spleen also rotates, and goes to the left
• The spleen is a VERY vascular organ, and originally it is hemopoeitic (remember it, along w/ the liver) ; So if there is splenic rupture, there could be EXTREME blood loss
What artery is the midgut supplied by?
• Superior Mesenteric Artery
How does the midgut maintain communication with the yolk sac?
• Vitello Intestinal Duct
What organs come from the midgut?
• 3rd and 4th part of the duodenum
• jejunum, ileum
• cecum, appendix
• ascending colon
• first 2/3rds of the transverse colon
Note: the extraembryonic ceolem is the same thing as the chorionic cavity
What happens to the midgut at the 4th week?
• The midgut is a U-shaped loop, and at the 4th week, it herniates through the abdominal ring, forming a Physiological Umbilical Herniation
• This physiological umbilical herniation will then go down around week 10-11
What are the 2 limbs of the midgut, and what do they give rise to?
• Cranial Limb: duodenum, jejunum, and the upper part of the ileum
• Caudal Limb: lower part of the ileum, ascending colon, proximal 2/3rds of the transverse colon and a cecal bud
• The cecal bud gives off the cecum, and the appendix
Volvulus
• Results from malrotation of the gut
• The intestines twist around the stomach
• Presents as vomiting (just like pretty much all the other GIT disorders)
What artery is the hindgut supplied by, and what does it form?
• Inferior mesenteric artery; distal 1/3 of the transverse colon; descending colon, rectum, and the upper part of the anal canal
• Also forms the ureter and the urethra
What structure is the HINDGUT connected to?
• The allantois
What does the distal end of the hindgut form?
• The cloaca, which contacts the surface ectoderm to form the cloacal membrane
What divides the cloaca, and what does it divide it into?
• Urorectal Spetum divides the cloaca into the urogenital sinus, and the primitive/primordial rectum
• So this is good – now we have 2 holes – one for the urine, and one for the feces
• Ultimately the urogenital sinus will form the bladder and the urethra
Where do the upper and lower portions of the anal canal come from?
• Upper portion of the anal canal = posterior rectum
• Lower portion of the anal canal = ectodermal anal pit
• SO: the upper part of the anus is endodermal, and the lower half of the anus is ectodermal.
What is the pectinate line?
• The line of demarcation between the ectoderm and the endoderm
Omphalocoele
- Failure of the reduction of the physiological hernia, so the intestines fail to come back into the abdominal wall
- Presents as a visceral sac of containing the abdominal viscera, protruding from the umbilicus
Meckel’s Diverticulum
- Remnant of the vitellointestinal duct, mainly on the ileum
- Very common
May present with pain similar to appendicitis – b/c it has gastric mucosa in it, and can become ulcerated
Imperforate Anus
- Anal membrane fails to perforate
- There is no exit for the feces
TRAFFIC JAM!!
Can be easily corrected surgically
Can be diagnosed by the baby failing to pass meconeum!
Gastroschisis
- Failure of the development of the anterior abdominal wall
- Presents the same way as Omphalocoele
Contents of the GI tract will be coming out the abdominal wall
Hirschbrung’s Disease
Aka
Colonic Aganlgiosis
- Failure of the neural crest cells to migrate and form the myenteric plexus in the sigmoid colon and the rectum
- Results in the inability to create peristalsis, in order to move out the feces
TRAFFIC JAM!!
This can be diagnosed by the baby’s failure to pass meconeum
Reusults in (rhyme): fecal retention, and abdominal distention
Where does the skeletal system develop from?
• Neural crest cells and the mesoderm
What role does the mesoderm play in the development of the skeletal system?
• It forms mesenchyme
• Mesenchyme – loose CT which is undifferentiated, and therefore can form fibroblasts, chondroblasts, and osteoblasts
What are the main steps in the development of cartilage?
• The mesenchymal cells grow and proliferate
• Chondroblasts secrete the matrix
• Interstitial and appositional growth occurs
- Remember? there are 3 types of cartilage: Hyaline, elastic, and fibrocartilage
What are the 2 types of bone development (ossification)?
• Intramembranous
• Endochondral
What is interzonal mesenchyme and what is its growth period?
• Mesenchyme which is located in between the bones
• It begins to grow at 6weeks, and it resembles adult joints at the end of the 8th week
What are the layers of the intraembryonic mesoderm?
• Paraxial
• Intermediate
• Lateral Plate
From where do somites come?
• Somites are from the paraxial mesoderm
What layers do the somites differentiate into, and what do those layers form?
• Dermatome – skin
• Myotome – muscle
• Sclerotome –verterbral column and ribs
Where do the mesodermal cells from the sclerotome migrate, and what do they form there?
• Notochord --> centrum
• Neural Tube --> vertebral arches
• Body wall --> costal process
What is the arrangement of the mesenchymal cells in the vertebral column?
• Loosely packed cranial cells
• Densely packed caudal cells
Describe the formation of the intervertebral segments
• The loosely packed cranial cells unite with the densely packed caudal cells in order to form a segment which has densely packed cells on the top, and loosely packed cells on the bottom
- Note: neural arches, costal processes, and transverse processes are also formed this way
What happens to the notochord in the vertebral body?
• The notochord degenerates in the body, but remains in intervertebral disks as the nucleus pulposus
How does the annulus fibrosis form?
• From the cranial migration of the densely packed cells
• i.e. from the sclerotome
What is the ossification process of the vertebra?
• The mesenchyme is first converted into cartilage
• There is a primary and a secondary ossification center
• The primary ossification center has 3 points: 1 for the body, and 2 for the neural arches
What happens if the neural arches do not fuse?
- Then the spinal cord is exposed --- SPINA BIFIDA
Describe the evolution of the vertebra from birth to 18 years
• At birth, you have 3 bony parts
• By 3-5 years, the neural arches fuse
• The centrum of the atlas and the axis fuse to form the odontoid process
• By the 18th year the intercalated disks of the sacrum fuse
Where do you get the ribs from and what kind of ossification do they undergo?
• The ribs are ventral extensions of the mesenchyme of the sclerotome
• They undergo chondrification, and later ossification in the thoracic region
Describe the development of the sternum
• A pair of mesenchymal vertical bars exist called “sternal bars”
• They fuse in a craniocaudal fashion
What will happen if the sternal bars do not fuse?
• The heart will be left exposed!!
What are fontanelles?
• Large fibrous areas where the sutures meet
How many fontanelles do we have, and where are they?
• 6: anterior, posterior, sphenoid, and mastoid
When do the fontanelles fuse?
• Posterior and sphenoid : at 6mos.
• Anterior and mastroid : at 18-24mos
What is the significance of fontanelles?
• They allow the babies brain to grow for the first 2 years of life
• Give us an indication of the babies hydration status – so a depressed fontanelle = a dehydrated will have a depressed fontanelle
• Important – when moving through vagina they babies head will be able to somewhat mold to the movement, rather than being crushed
Chordoma
- Tumor resulting from the notochord remnants
- A huge bulge/tumor which can be present anywhere in the axial skeleton, but is usually at the base of the coccyx
Achondroplasia
- Impaired development of cartilage
- Dwarfism – impaired development in the epiphyseal plate this is why midgets usually have normally sized heads, but disproportionately small limbs – the cartilage is in the epiphyseal plate
Klippel Feil Syndrom
- Malformation of the cervical vertebrae; not spaced apart as they should be; instead they sit right on top of each other
- Short neck; head appears to rest on the shoulders
Accessory Ribs
- Usually in the cervical region
- They can compress the brachial plexus or subclavian arteries
Spina Bifida
- Failure of the 2 neural arches to fuse
- Spina Bifida Occulta – no clinical symptoms; everything is normal
Spina Bifida Cystica – the spinal cord and meninges are involved
Meningocoele
Myocele
Coming out only meninges
Myocele – coming out meninges AND spinal cord
Where and when do limb buds form?
• On the ventrolateral wall of the body
• At the 4th week
Which forms first, the upper limbs or the lower limbs?
• The upper limbs form first
What induces limb growth?
• The apical ectodermal ridge – it’s the thickened portion of the tip of each limb
• It induces the underlying mesoderm to grow
• It determines the proximodistal axis of the limb
• So no apical ectodermal ridge = NO LIMB GROWTH!!!
What is the AER regulated by?
• The fibroblast Growth factor
What does each limb consist of?
• Ectoderm
• Mesoderm from the somatic layer of the lateral plate mesoderm
• Apical Ectodermal Ridge (AER)
What is at the base of the limb bud?
• The Zone of Polarizing Actvity
• This controls the polarity of the anteroposterior surface of the limb
What forms what?
1) Lateral Plate
2) Neural Crest Cells
3) Neural Tube
4) Somites
1) Blood vessels, CT and bone
2) Melanocytes, schwann cells, sensory axons, DRG
3) axons
4) axial skeleton and musculature
Initially how are the thumb and the great toe?
- cranial
What is the rotation that occurs in the limbs?
• The upper limb rotates 90 degrees laterally
• The lower limb rotates 90 degrees medially
What do somites in the trunk region form?
- myotomes
How does the formation of the trunk muscles occur?
• Somites give rise to myotomes
• Myotomes give rise to
- Dorsal Epimeres – which give us the back muscles
- Ventral Hypomeres – prevertebral, intercostals, and abdominal muscles
Genetic Abnormalities
- Polydactlyl – extra digit
- Syndactyly – “webbed” digits as a result of the failure of apoptosis of the cell tissue in b/w
Teratongenic
- Phocomelia – common malformation seen with thalidomide where the baby has limbs which are attached VERY close to the trunk
Mechanical
- Oligohydraminous – limb malformation due to decreased amount of amniotic fluid
- Bicornate uterus – Uterus has 2 hors so there’s not enough room for the fetus to grow; usually results in spontaneous abortion
- Sirenomelia – assoc. w/uncontrolled gestational diabetes – caudal regression syndrome