Development of the digestive tract AHS1 Flashcards
What is gastrulation?
Formation of the trilaminar germ disc/three layers
What are the two different types of lateral plate mesoderm?
Somatic and splanchnic
What area of the body is somatic lateral plate mesoderm?
Body wall
What area of the body is splanchnic lateral plate mesoderm?
Viscera
Also muscle layers of the gut tube (even though rest of GI tract is endoderm)
What does the ectoderm make?
Nervous system, adrenal medulla, skin
What does the mesoderm make?
Bone, cartilage, muscles, CV system, limbs, UG tract, spleen
What does the endoderm make?
The lining of the gut, GI tract accessory organs (liver, pancreas etc.). respiratory tract (the parts of the body that have openings to the outside)
What layer are the lips derived from?
The ectoderm
What layer are the mucous membranes
Endoderm
What is the area where the endoderm and ectoderm come in contact to form the mouth called?
Oro-pharangeal membrane
What is the area where the endoderm and ectoderm come in contact to form the anus called?
Anal membrane
What does the septum transversum form?
The diaphragm and cranioventral mesentery
What mesenteries does the foregut have?
Dorsal and ventral mesentery
turn into mesoduodenum etc. when the GI tract starts to differentiate into different parts
What mesenteries does the midgut have?
Only a dorsal mesentery (due to amniotic sac formation)
What mesenteries does the hindgut have?
Dorsal and ventral mesenteries
How does the stomach start to develop?
By forming a bulge dorsally in the GI tract
Where does the spleen develop from?
From the mesoderm (rather than the endoderm like the GI tract)
Where does the spleen develop in the abdomen?
In the dorsal mesogastrium/mesentery
How does the stomach further develop in the abdomen/twist?
It rotated 90 degrees anticlockwise around the cranio-caudal axis so that the greater curvature is on the left (or right looking ventrally).
It then rotates 45 degrees to run more transversely so top is on the left and bottom is on the right.
How are the other organs affected by the rotation of the stomach?
The spleen in the dorsal mesentery is pulled to the left as the greater curvature of the stomach is pulled to the left
The liver in the ventral mesentery is pulled slightly to the right
How does the greater omentum form?
The dorsal mesogastrium/mesentery comes off the greater curvature of the stomach and folds back on itself
How does the lesser omentum form?
From the ventral mesogastrium running cranially to the liver from the lesser curvature of the stomach (the stomach curls round)
Where do the liver and pancreas arise from?
From the gut tube near the foregut/midgut boundary
Why is the liver closely associated with the diaphragm?
Because the liver bud invades the septum transversum
What is the septum transversum?
Cranial mesenchyme that gives rise to the diaphragm and the ventral mesentery of the foregut
How do stomach rotations affect the pancreas?
They bring the pancreatic buds together to fuse to form a single pancreas with two lobes
In what animals are there separate openings of the common bile duct and accessory pancreatic duct?
Dog, horse and human - others are different with either pancreatic ducts and bile ducts sharing one opening of two completely separate ducts
How does the midgut twist in development?
It extends into the umbilicus
It then twists 180 degrees clockwise around the root of the mesentery
It then retracts back into the abdomen and twists another 90 degrees
Where is the caecum located in the abdomen?
On the right hand side
Which way does the transverse colon pass behind the root of the mesentery?
From the right to the left
Which side of the abdomen is the descending colon on?
The left side
right side looking ventrally
How does the hind gut develop?
The reproductive tract and the GI tract separate and the anal membrane breaks to form a hole
What are the complications with hindgut formation?
Anal atresia - anal membrane doesn’t break down
What are the main vessels of the umbilicus?
Umbilical arteries and umbilical vein
What does the umbilical vein do?
Takes oxygenated blood from the mother into the foetus
Where does the umbilical vein lead?
Into the ductus venosus
What do the umbilical arteries do?
Carry the deoxygenated blood out of the foetus
Where are the umbilical arteries?
Next to the urachus
What is the urachus?
Primitive bladder - takes the urine in the foetus down the umbilicus form the bladder to the allantois
What happens to the urachus after birth?
The lower part shrivels up and the upper part forms the bladder
What does the umbilical vein turn into?
The teres/round ligament
What is the falciform ligament?
A fold in the ventral mesogastrium/peritoneum that is full of fat
Where is the falciform ligament located?
Next to the teres ligament cranial to the umbilicus
What do the umbilical arteries turn into?
The proximal part - cranial vesicle arteries
The distal part - round ligaments of the bladder
What are the cranial vesicle arteries?
Arteries that supply the bladder that are derived from the umbilical arteries
What does vesicle mean?
Bladder
What are the ligaments that form around the bladder?
The lateral vesicle ligaments and the median vesicle ligament
What are the lateral vesicle ligaments derived from?
Folds in the ventral mesogastrium/peritoneum around the umbilical arteries
Where is the median vesicle ligament derived from?
A fold in the ventral mesogastrium/peritoneum which comes up from the ventral peritoneum
