3 Development of the Gastrointestinal tract Flashcards
How is the primitive gut tube created?
Embryonic folding- 4th week
Lateral folding
Ventral body wall
Primitive gut= tubular
Craniocaudal folding
Creates cranial and caudal pockets
What is the gut tube?
Endoderm lined tube
Runs length of body
Has blind pouches at head and tail ends
Opening at umbilicus
Splanchinic mesoderm covering
(development begins week 3)
Label the parts of the primitive gut tube:
List the derivatives of the foregut, midgut and hindgut respectively. (remember where they divide)
Divisions:
Foregut-Midgut= bile duct entrance in duodenum
Midgut- Hindgut= 2/3 along transverse colon
Each embryonic gut receives blood supply from a distinct branch of the abdominal aorta. What are these branches?
Why do the duodenum and the pancreas have mixed blood supplies? Describe the blood supply to the duodenum
Structures develop close to junction between foregut and midgut
- Duodenum
- Celiac trunk
- Gastroduodenal artery
- Superior pancreaticoduodenal
- Superior mesenteric
- Inferior pancreaticoduodenal
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- Inferior pancreaticoduodenal
- Celiac trunk
Describe the blood supply to the pancreas
Pancreas (head)
Celiac
Superior pancreaticoduodenal
Superior mesenteric
Inferior pancreaticoduodenal
What is the internal lining of the gut tube derived from and what does it eventually become?
Derived from: Endoderm
Becomes: Epithelia
What is the external lining of the primitive gut tube made from and what does it eventually become?
Derived from: Splanchnic mesoderm
Becomes: Future musculature and peritoneum
What are the 2 layers that the mesoderm split into?
- Somatic (abdominal wall)
- Splanchnic (smooth muscles of gut wall and peritoneum)
The space created by the splitting of the 2 mesoderm layers is the coelomic cavity. What does the coelomic cavity eventually become?
Pleural cavity
Peritoneal cavity
What are mesenteries and what is their function?
Double layer of peritoneum- suspending gut tube from abdominal wall
Function:
Allow passage of blood and nerve supply
Allow mobility when needed
All 3 regions of the embryonic gut tube are suspended from the dorsal body wall by the dorsal mesenteries. Which region is the only region with a ventral mesentery?
Foregut
Ventral mesentery attaches foregut to floor of abdominal cavity
What are omenta? (general terms)
Specialised regions of peritoneum
Where are the greater and lesser omenta formed from?
- Greater: dorsal mesentery
- Lesser: ventral mesentery
What does the free edge of the lesser omentum facilitate the conduction of?
Portal triad
Give examples of 2 parts of the GI tract that remain suspended from the posterior abdominal wall by a mesentery and remain mobile.
Jejunum
Ileum
What does it mean to be:
- Retroperitoneal
- Secondarily retroperitoneal
- Retroperitoneal
- Structure not suspended in abdominal cavity
- Were never in peritoneal cavity and never had a mesentery
- Secondarily retroperitoneal
- eg pancreas and duodenum
- Began development invested in peritoneum
- Had mesentery
- Eventually mesentary lost through fusion of posterior abdominal wall
How does the gut become open to the exterior at the future mouth and anus?
Forgut- blind end: Oropharyngeal membrane
Hindgut- blind end: Cloacal membrane
Membranes break down- gut opens to exterior
What does the rotation of the stomach result in the formation of?
Rotation of stomach- results in formation of greater and lesser sacs
How does the separation of the GI and Respiratory tracts occur in the developing embryo?
Formation of respiratory diverticulum
In ventral wall of foregut
4th week
(Can go wrong- cause variety of abnormalities)
How does the stomach acquire its characteristic shape (greater curve) and position?
SHAPE: Dorsal border develops faster than ventral
POSITION: Week 4, slight dilation of distal foregut
Where do the liver and the biliary system develop from?
Ventral mesentery
Where does the pancreas develop from? (different parts- different places)
- Ventral mesentery
- Uncinate process
- Inferior head
- Dorsal mesentery
- Superior head
- Neck
- Body
- Tail
How does the duodenum become secondarily retroperitoneal?
Rotation of stomach- pushes duodenum right, then against posterior abdominal wall
The lumen of the duodenum is obliterated in the 5th and 6th weeks of development. When is it recanalised?
End of embryonic period
How many layers of peritoneum make up the omenta?
4 layers
