Development Of The Foregut Flashcards
Where does the foregut start and end?
Distal oesophagus
To
Halfway along the duodenum (1st and 2nd parts of the duodenum are foregut)
Where does the midgut start and end?
Halfway along the duodenum (just distal to the entrance of the bile duct – 3rd and 4th parts of duodenum are midgut)
To
Junction of the proximal 2/3 of the transverse colon with the proximal 1/3 (first 2/3 of the transverse colon are midgut)
Where does the hindgut start and end?
Distal 1/3 of the transverse colon
To
Upper anal canal
What is the arterial supply of the foregut?
Coeliac trunk
What is the sympathetic and parasympathetic innervation for the foregut?
S: Greater splanchnic n. (T5 – T9)
P: Vagus
Where is visceral pain of the foregut felt?
Epigastric region
What is the arterial supply of the midgut?
Superior mesenteric artery
What is the sympathetic and parasympathetic innervation for the midgut?
S: Lesser splanchnic n. (T10-11)
P: Vagus
Where is visceral pain of the midgut felt?
Umbilical region
What is the arterial supply of the hindgut?
Inferior mesenteric artery
What is the sympathetic and parasympathetic innervation for the hindgut?
S: Least splanchnic n. (T12 +/- L1) and lumbar splanchnic nerves
P: Pelvic splanchnics
Where is visceral pain of the hindgut felt?
Suprapubic region
What does the bilaminar disc develop from?
Develops from the inner cell mass
What happens in gastrulation?
Primitive streak forms on the epiblast
Epiblast cells migrate to the primitive streak and invaginate through it
Some cells displace the hypoblast and form the endoderm
Some cells create a new layer between the epiblast and endoderm = mesoderm
Epiblast = ectoderm
What does the ectoderm layer give rise to?
CNS and PNS
Skin, hair and nails
Pituitary gland, sweat glands, tooth enamel
What does the mesoderm layer give rise to?
Muscle, cartilage and bone
Urogenital system, spleen and adrenal cortex
Connective tissue of the gut wall, pancreas and liver
Visceral peritoneum
What does the endoderm layer give rise to?
Epithelium of the GI tract, respiratory tract
Hepatocytes (cells of the liver)
Endocrine and exocrine cells of the pancreas
What does inner cell mass develop into?
Human beings
What does outer cell mass develop into?
Placenta
What can failure of closure of the ventral body wall in the thoracic region lead to?
Ectopia cordis
What can failure of closure of the ventral body wall in the abdomen lead to?
Gastroschisis
What can failure of closure of the ventral body wall in the pelvic region lead to?
Bladder exstrophy
What does the foregut develop into?
Oesophagus
Stomach
First half of the duodenum (1st and 2nd parts)
What are the derivatives of the foregut?
Liver
Pancreas
What are the mesenteries of the foregut?
Dorsal mesentery
Ventral mesentery
What is the ventral mesentery?
Arises from the septum transversum
The liver grows into it, and splits it into the lesser omentum and the falciform ligament
What is the lesser omentum?
Connects the liver to the stomach and duodenum
What is the falciform ligament?
Connects the liver to the anterior abdominal wall
What type of muscle does the upper 2/3 of the oesophagus contain?
Striated muscle
What type of muscle does the lower 1/3 of the oesophagus contain?
Smooth muscle
What is the upper part of the oesophagus innervated by?
Vagus nerve
What is the lower part of the oesophagus innervated by?
Splanchnic nerves
What happens to the stomach during embryonic development?
This section of the gut tube starts to dilate in week 4
Changes shape due to different rates of growth of different parts
Changes position – rotates 900 clockwise around its long axis: brings the left side to lie anteriorly and the right side to lie posteriorly
Brings duodenum to the right
What happens to the liver during embryonic development (Day 25-32)?
Liver bud is an outgrowth from the distal foregut (endoderm epithelium) - appears in week 3
Cells proliferate - grow into the septum transversum
Connection between the liver bud and foregut (duodenum) narrows > bile duct
What happens to the liver during embryonic development (Day 36+)?
Small outgrowth from the bile duct > gallbladder
As the liver grows, the remaining mesoderm either side becomes membranous > falciform ligament and lesser omentum
What happens to the pancreas during development?
Dorsal and ventral buds arise from the duodenum
Dorsal bud develops in the dorsal mesentery
Rotation of the stomach swings the ventral bud posteriorly
Dorsal and ventral buds fuse
What are the final positions of the foregut viscera?
Rotation of the stomach brings its left side to lie anteriorly and swings the duodenum to the right
The dorsal mesentery along the greater curvature bulges down and grows – the greater omentum.
This becomes fixed to the mesentery of the transverse colon (and posterior wall).
Rotation alters the position of the mesenteries, omenta and peritoneal ligaments
Some organs are brought into contact with the posterior abdominal wall (e.g., the pancreas and duodenum) and become retroperitoneal
A small space behind the stomach – the lesser sac – is formed
