GI Embryology Flashcards
What is the main artery that supplies the GI Tract?
Abdominal Aorta
What are the branches of the Abdominal Aorta and what parts do they supply?
Celiac Trunk (Foregut) Superior Mesenteric (Midgut) Inferior Mesenteric (Hindgut)
Which Vein drains the fore-gut?
The Portal Vein
What is the primitive gut tube made from?
Enfolding of the Endoderm
Where is there a mixed blood supply?
Between the areas of foregut and midgut
Where is the boundary less defined?
Between mid and hindgut
How is the intraembryonic coelum divided?
By the future diaphragm into thoracic and abdominal cavities
What does the intraembryonic coelum connect with?
The extra-/yolk sac
What is a mesentery?
A double layer of peritoneum
Made up of condensation of splanchnic mesoderm
They suspend the gut tube from the posterior abdominal wall
Allow a passage for VAN supply
Allow mobility where needed
Divide the sac into greater and lesser
What does the ventral mesentery attach to?
Just the foregut
What does the stomach rotation do?
The mesenteries -> Greater and Lesser omenta and
They form the greater and lesser sacs
What is the lesser sac?
It is a closed pouch/recess of the abdomen, formed by the mesenteries
It has one opening- the epiploic foramen
What does the lesser omentum attach to?
The liver and proximal duodenum (connection is the foramen) and the lesser curve of the stomach
What does the greater omentum attach to?
Greater curve of the stomach
Proximal duodenum
Transverse Colon runs through
Transverse colon attaches to ventral wall by the transverse mesocolon (mesentery)
How does the stomach form?
It is a fusiform dilation of the foregut
It enlargens, the left side faster than the right
There is 90 degree rotation so the right side faces posteriorly
How does the oesophagus form?
It is the narrowest part of the foregut, it lengthens and proliferates rapidly.
There is then formation of a respiratory diverticulum which seperated the trachea and oesophagus (tracheoesophageal septum)
This causes the lumen to be o
Why can Atresia of the Oesophagus occur?
Whilst it lenthens, it proliferates rapidly and can obliterate the lumen, so needs recanalisation otherwise atresia and stenosis can occur
Where are foregut glands formed?
Liver is formed in the ventral mesentery (and Biliary System, Part of Pancreas*)
Spleen is formed in the dorsal mesentery (And Most of Pancreas
*They fuse with stomach rotation
How does the liver grow?
Develops from the hepatic bud
Earliest GI gland to develop
Grows rapidly and takes up space in the abdomen
Grows and gets rid of top part of peritoneum (to get bare area), joins with lesser omentum to duodenum and stomach
Ventral mesentery also forms the falciform ligament of the liver
How does the duodenum develop?
It is from mid and hindgut
Grows rapidly, needs recanalisation
Rotation of stomach put it it to the right and posteriorly (2ndary retroperitoneal)
Forms a C shaped loop
Which week does the midgut start growing?
Week 6
How does the midgut develop?
Overview..
It elongates rapidly to create the primary interstitial loop (it loops as not enough space in the intraembryonic coelum)
It herniates, rotates and returns to the cavity
What are some features of the loop?
the superior mesenteric artery is the axis.
It has cranial and caudal limbs.
It has the vitilline duct which connects it to the yolk sac
Describe the herniation
It is physiological.
The intestines herniate into the proximal part of the umbillical cord.
As it rotates anticlockwise the cranial limb becomes very convuluted to become the small intestine (to the proximal ileum)
The caudal create a caecal swelling, drops down to produce the asc. colon.
The midgut rotates 90 3 times, so the cranial limb returns first and moves left
What are the 2 types of malrotation?
Incomplete - if midgut only rotates the first 90, produces the left sided colon
Reversed - The colon rotaes one 90 clockwise so the transverse colon passes posteriorly to the duodenum.
Leads to volvulus, strangulation and ischaemia
You can also get subhepatic coecum
How can the yolk stalk persist?
Vitelline Cyst - Duct forms fibrous strands, can have volvulus
Viltelline Fistula - Direct communication, leads to leaking at umbillicus
Meckel’s Diverticulum - Most common, creates an outpouching, can have ectopic gastric/pancreatic tissue (enzymes can cause inflammation)
Why can Atresia/Stenosis occur?
And Where?
As the lumen is obliterated in the small intestine, gallbladder and oesophagus due to rapid growth.
If recanalisation fails, it can occur
What is Pyloric Stenosis?
Where there is hypertrophy of the circular muscle in the pyloric sphincter.
What is Gastroschisis?
“Split Stomach”
The abdominal wall doesn’t close in folding, so the gut is outside the body cavity
What is Omphalocoele?
Persistance of the physiological herniation, not covered in tissue
What is the Hindgut?
The distal 3rd of the transverse colon up to the rectum
Includes epithelium of the bladder
Describe the Anal Canal
Divided by the pectinate line, as histologically distinct.
How does the epithelia differ by the pectinate line?
Above- Columnar
Below - Stratified Squamous
What is the blood supply and innervation of the 2 parts of the anal canal?
Above- inferior mesenteric artery and S2-4 pelvic (parasympathetic, stretch)
Below- Pudental Artery
S2-4 Pudental Nerves (somatic, pain)
How does the anal canal develop?
Division of the cloaca
Once the septum hits the membrane, it ruptures and disappears, as it is avascular. Creates a perineal body
What are some abnormalities of the hindgut?
Imperforated anus
Agenesis
Hindgut fistulae
