Development of the GI Tract Flashcards
The structures in the primitive embryo
Ectoderm
Mesoderm
Endoderm
What does the ectoderm form
Brain, spinal cord, skin, epithelia
What does the mesoderm form
Connective tissues, bones, cartilage, blood, muscle
What does the endoderm form
Guts
Formation of the primitive gut
Trilaminar disk folds in on itself
Left of ectoderm forms brain
Right of ectoderm forms bottom of spinal cord
Left of endoderm forms pharynx, oesophagus, stomach, duodenum
Middle of endoderm forms jejunum, ileum, caecum, asc colon
Right of endoderm forms desc colon, caecum, rectum
Top of allantois forms part of urinary tract
Structure of the embryo once the trilaminar disk folds in on itself
Coelomic cavities form peritoneum either side of gut tube
Structure and function of the mesenteries
Double fold of peritoneum forms mesentery
Allows blood vessels like abdominal aorta, blood supply => gut tube
Foregut only has ventral mesentery
Fore, mid, hind gut has dorsal mesentery
Aorta
Dorsal mesogastrium
Gut tube
Ventral mesogastrium
The vitelline duct and allantois, blood supplies
Mid and hind gut don’t have anterior connection, connected to yolk sac and allantois, form umbilical cord
Coeliac trunk supplies foregut, comes off aorta
Superior mesenteric artery supplies midgut, part of umbilical cord and vitelline duct
Inferior mesenteric artery supplies hindgut
Umbilical arteries pass into umbilical cord
Structure of the foregut
Pharynx, oesophagus Lower respiratory tract Stomach Duodenum Liver, pancreas Biliary apparatus
Pharynx formation
Empty canal
Canal filled up with cells
Vacuoles form in canal
Forms canal
Problems in pharynx formation
Stenosis = lumen too narrow Duplication = 2 canals form, bacteria can accumulate Atresia = canal is closed off
Lower respiratory tract formation
Respiratory diverticulum buds off from oesophagus
Tracheooesophageal septum forms during separation
Forms pharynx and trachea
Trachea forms lung buds
Problems in oesophagus and trachea formation
Atresia of oesophagus
Fistula formation between trachea and oesophagus
Atresia and fistula formation
Development of pancreas
Dorsal pancreas buds off on L
Ventral pancreas, gall bladder and hepatic system branch off from bud on R
Ventral pancreas grows and rotates around joins w dorsal pancreas to form 1 pancreas (becomes the asinate process)
Ductal system passes from dorsal pancreas to ventral pancreas into duodenum
Structures in the midgut
Duodenum, distal to bile duct opening Jejunum and ileum Caecum and appendicitis's Asc colon Proximal 2/3 of transverse colon
Midgut umbilical herniation
Midgut = cranial limb Hindgut = caudal limb
Stage 1 = elongation
Intestines herniate out due to rapid growth and
Stage 2 = 90 degree anticlockwise twist
Stage 3 = 180 degree anti clockwise twist, elongated tubes brought back into abdominal cavity
Eventually large bowels are on the right, small bowel ends up on left
Abnormal midgut rotation
Reversed rotation
Non rotation
Mixed rotation
Reversed rotation
Stage 3 reversed, clockwise
Duodenum in front of large bowel instead of the other way around
Non rotation
Small bowels and large bowels end upon opposite sides
Transverse colon bunched up
Mixed rotation
Caudal, cranial limb movement not coordinated, no rotation
Intestinal loops form volvulus
Twists blood supply to gut, dies
Omphacoele
More space in umbilical cord than abdominal space
Intestines end up in umbilical cord instead
Gastroschisis
Intestines end up in area lateral to umbilical cord
Potentially linked to mother’s cocaine and drug use
Meckels diverticulum
2 inch out pouching of small bowel, 2 feet from iliocaecal junction
Left over from umbilical cord, vitelline duct is not fully absorbed
Structures in hindgut
Distal 1/3 of transverse colon Desc colon Sigmoid colon Rectum Superior part of anal canal Epithelium or urinary bladder, most of urethra
Structure of the hind gut region
Urogenital septum between but doesn’t separate hind gut and cloaca
Urogenital septum between vitelline duct and allantois
Cloaca covered by cloacal membrane
Function of cloaca
Forms rectal canal, urethra, blind ended by membrane
Only opens up when membrane broken
Development of hindgut region
Urogenital septum separates urinary and rectal exits
Cloacal membrane thins
Proximal allantois => proximal urinary bladder
Proximal anal canal formed from hindgut
Distal anal canal formed from proctodeum
