Embryology of the GI Flashcards
what are the phases for human development?
Growth, morphogenesis and differentiation
Give examples of teratogens and during what weeks can they cause major abnormalities
Viruses and Drugs; weeks 4-8
What is gastrulation
process by which the 3 germ layers and axial orientation of embryo is established
What happens during gastrulation
Bilaminar embryonic disc is converted to trilaminar
Ectoderm Gives rises to:
Epidermis,CNS,PNS,retina of eye etc
Endoderm gives rises to:
Epithelial Lining of RS,GIT,glands,lier and pancreas
Mesoderm gives rise to:
Most of CVS, connective tissue,muscles, blood cells,bone marrow,Vessels associated w organs and tissues
Primordial Gut forms during?? Derived from??? Closed at cranial and caudal end by??
4th week, From endoderm of yolk sac,cranial: oropharyngeal membrane
Caudal: Cloacal membrane
Foregut develops form?? What develops from ventral wall of foregut??
Cranial part of the primitive gut tube. Laryngo-tracheal diverticulum
When does foregut dilate to become stomach?
4th week
Rotation of stomach and direction? What kind of rotation
90 degrees clockwise making ventral border left side and dorsal right side. ANterio-posterior rotation
What mesentry attaches to stomach?Which mesentery goes to the left to create the omental bursa?
Mesogastrium.
Ventral mesentry
Duodenum formed from which part of midgut and foregut?
the caudal part of the foregut and the cranial part of the midgut
Blood supply to duodenum???
Coeliac axis and Superior mesenteric artery
What’s the part of duodenum that retains its dorsal mesentry?
Duodenal Cap
When does the liver primordium appear?
Middle of 3rd week by Outgrowth of endoderm (epithelia) in the distal end of the foregut
What forms the bile duct and what does its ventral outgrowth do?
Connection bw liver bud and foregut (duodenum). Ventral growth of bile duct forms gallbladder and cystic duct
What side is the spleen on? How does it form? When does it differentiate to become the spleen?
end of 4th week. By mesenchymal condesnsation on dorsal mesogastrium near body wall. Differentiates during 5th week to become spleen
Spleen derived from??
Mesodermal and NOT endodermal
Up to what week does the spleen act like a haematopoietic organ?
week 14
What happens from week 15- 17
Spleen acquires its lobular shape and is colonised by T lymphocyte cells
When do the B cell precursors arrive? What does this mean?
Week 23. Spleen can start its lymphoid function
Pancreas forms from how many buds? which grow from where? When do they join?
Endodermal lining of duodenum IN WEEK 5. (foregut)
2 buds : dorsal and ventral
Week 6 they lie closer together at the dorsal part
Ventral part forms which part of pancreas
Inferior part of head of pancreas and uncinate process.
Main pancreatic duct formed by?
Ventral duct and distla part of dorsal duct
Proximal part of dorsal duct may form:
Accessory duct
When does an annular pancreas form? What can this cause?
When the ventral bud fails to migrate around the duodenum correctly
-Duodenal stenosis
Where does the midguut extend
Distal part of duodenum –> first 2/3rds of transverse colon
primary intestinal loop: Cephalic part becomes:
distal duodenum,jejenum, and proximal ileum
Caudal part of intestinal loop:
Distal ileum, caecum, appendix, ascending colon and the proximal 2/3rds of the transverse colon
Primary gut tube must undergo:
Physiological herniation
When does rotation of primary gut tube happen? Around which axis? Rotation in which direction first? What part is carried where?
Week 6. Around axis of superior mesenteric artery. 90 degrees anticlockwise. Cranial part of midgut carried to right side
Into what does the gut tube herniate
Extraembryonic cavity in the umbilical cord
When do the intestinal loops begin to move from umbilical cord back to abdominal cavity?
10th week
What enters abdominal cavity in what direction and what is the last part to enter
proximal part of jujenum into the left side and the last part to enter is the caceum
What happns after the gut tube returns to the abdominal cavity
180 degree rotation anticlockwise further
What does this rotation establish
that the transverse colon is in front of the duodenum
What is an omphalocele?
Herniation of abdominal organs through an enlarged umbilical ring but the organs are covered in an amnion
What is gastroschisis?
Herniation of abdominal contents directly to amniotic cavity but not covered by amnion or peritoneum usually due to cocaine use?? not associated with chromosomal abnormalities
What is Meckel’s diverticulum?
A diverticulum formed by a small vitelline duct that persists in 2-4% of people that may form a fistula or vitelline cyst or ligament
Hindgut made up of?
Distal 1/3rd transverse colon, descending colon, sigmoid colon, rectum and upper part of the anal canal.
-Endoderm of hindgut also forms the lining of the bladder and urethra
What does the terminal portion of the hindgut join
posterior part of cloaca (primitive anal canal)
Cloaca??
endoderm lined cavity with surface ectoderm at its ventral boundary
When does the cloacal membrane rupture? What happens after?
End of week 7
Ectoderm of the anal canal proliferates to close the caudal end
When does the anal canal reopen
Week 9
Cudaal anak canal is derived from
Ectoderm
