GI embryology - development of the peritoneum and foregut Flashcards
In the fourth week what two types of folding occur?
Lateral and craniocaudal folding
What are the affects of lateral folding?
- Creates ventral body wall
2. Primitive tube becomes tubular
What are the affects of craniocaudal folding?
- Creates cranial and caudal pockets from yolk sac endoderm (beginning of primitive gut development).
When does the primitive gut tube begin to develop?
Week 3 when it pinches off from the yolk sac cavity.
What is the stomatodeum?
Future mouth (stomata=primitive mouth)
What is the proctodeum?
Future anus (procta=anus)
Describe the morphology of the primitive gut tube
It runs from the rostral stomatodeum to the caudal proctodeum, with an opening at the umbilicus.
Which of the three trilaminar layers is the primitive gut tube derived from?
Endoderm - interling lining -> future epithelial linings
Splanchnic mesoderm - external lining -> future musculature of gut wall and visceral peritoneum.
Which new cavity is the primitive tube suspended in by a double layer of splanchnic mesoderm?
Intraembryonic coelom
Describe the adult derivatives of the foregut
Oesophagus -> duodenum (proximal to entrance of bile duct)
Describe the adult derivatives of the midgut
Duodenum (distal to entrance of bile duct) -> proximal 2/3 of transverse colon.
Describe the adult derivatives of the hindgut
Distal 1/3 of transverse colon -> upper anal canal (to the pectinate line).
Also includes the internal lining of bladder and urethra.
What is the pectinate line?
A line 2/3 down the anal canal which corresponds to the developmental junction between the hindgut and the proctodeum.
What reflects the embryonic derivates of the foregut, midgut and hindgut?
Blood supply
Lymphatic drainage
In the fourth week, what constitutes the ends of the foregut?
At the cranial end the lung bud and at the caudal end, the liver bud.
In the fourth week, what happens to the ventral wall of the foregut at the junction with the pharyngeal gut?
A respiratory diverticulum (blind-ended tube) forms creating the respiratory primordium (ventral) with the oesophagus (dorsal).
What is the name of the tissue that divides off the respiratory primordium from the oesophagus?
Tracheoesophageal septum.
Up to 1 in 3000 live birth can have oesophageal abnormalities. Describe what abnormalities can occur.
Consequences of abnormal positioning of the tracheoesophageal septum. The following (individually or in combination):
- Proximal blind-end oesophagus
- Tracheoesophageal fistula (abnormal connection between oesophagus and trachea)
- Distal blind-end oesophagus
In the middle of the fourth week a slight dilation in the distal foregut indicates the position of what?
The stomach primordium.
What side of the stomach primordium creates the greater curvature?
The dorsal border - which has a faster growth.
Name the foregut derived glands.
Liver
Pancreas
Biliary System
Which foregut derived glands are derived from the dorsal mesentery?
Pancreas (superior head, neck, body and tail).
Which foregut derived glands are formed in the ventral mesentery?
Part of the pancreas (uncinate process and inferior head)
Liver
Billiary system
Which is the earliest GI tract associated glands which develops?
The liver
Where does the liver develop?
The hepatic bud develops in the ventral mesentery and occupies a large part of the abdomen during development.
What is the name of the area of the liver that is not covered by the shiny, moist peritoneum and is attached to the diaphragm?
Bare area
What is the falciform ligament?
The remains of the ventral mesentery which connects the liver to the anterior abdominal wall?
What are the developmental derivatives of the duodenum?
It develops from the caudal foregut and the cranial midgut.
Why does the duodenum become a C-shaped loop?
Due to rotation of the stomach
What happens to the lumen of the duodenum during the 5th and 6th week of development?
The tissue surrounding the lumen becomes so thick it is obliterated. It is then recanalised by the end of the embryonic period.
What effect does rotation of the stomach have on the position of the duodenum?
It pushes it to the right and posterior - against the posterior abdominal wall.
What is meant by secondarily retroperitoneal?
A structure which develops intraperitoneally but is pushed back against the parietal peritoneum of the posterior abdominal wall, during the rapid development of the GI tract, and the mesentery of the structure fuses with the fascia.
The parietal peritoneum then grows back over this structure.
Name two secondarily retroperitoneal structures?
The pancreas.
The duodenum, except the duodenal cap (the first part of the duodenum attached to the stomach).
What is the yolk stalk attached to?
Endometrium of mother
In which cavity is the primitive gut tube suspended and by what?
Intraembryonic coelom.
Suspended by a double layer of splanchnic mesoderm.
Each embryonic segment receives a blood supply from a distinct branch of which vessel?
Abdominal aorta.
What is the name of the aorta branch that supplies the foregut?
Coeliac trunk.