Development of the foregut Flashcards
Where does the foregut start and end?
Distal oesophagus and ends halfway along the duodenum (1st and 2nd parts of the duodenum are foregut)
What is the arterial supply to the foregut?
Coeliac trunk
What is the innervation from the ANS to the foregut?
Sympathetic: Greater splanchnic (T5-T9)
Parasympathetic: Vagus
Where is visceral pain felt from the foregut?
Epigastric region
What does the bi-laminar disc form from?
Inner cell mass - becomes the human
outer cell mass - becomes the placenta
When does gastrulation occur?
In the third week
What is 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 (ectoderm) and endoderm = mesoderm
What doe the ectoderm become?
- CNS and PNS
- Skin, hair and nails
- Pituitary gland, sweat glands, tooth enamel
What does the mesoderm become?
- 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 become?
- Epithelium of the GI tract, respiratory tract
- Hepatocytes (cells of liver)
- Endocrine and exocrine cells of the pancreas
What does lateral folding achieve?
Makes us more tubular rather than flat
Where do the lateral folds grow?
They grow down and around the yolk sac
What does the paraxial mesoderm layer give rise to?
The visceral and parietal layers
What direction does the cephalo-caudal folding occur?
Down and in, heading up to leave the yolk sac outside
What is the dorsal mesentery?
A fold of peritoneum that attaches to the posterior wall behind the developing gut tube
What determines how the gut tube differentiates?
- It starts to differentiate whilst lateral folding is bringing the ventral body wall together
- Concentration gradient of retinoic acid starts to specify the different parts
- lowest levels cranially so near oesophagus and high levels distally
- Differential expression of transcription factors and genes along the tube specify how regions will develop
What are the two mesenteries of the foregut?
- The dorsal mesentery
- The ventral mesentery
Where does the ventral mesentery arise from?
It arises from the septum transversum and the liver grows into it and splits it into 2
What two spaces does the ventral mesentery become?
- The lesser omentum: connects the liver to the stomach and duodenum
- The falciform ligament: connects the liver to the anterior abdominal wall
Describe the upper 2/3 of the oesophagus
- Striated muscle
- Innervated by the vagus nerve
Describe the lower 1/3 of the oesophagus
- Smooth muscle
- Innervated by the splanchnic nerves
How does the oesophagus come about?
- A respiratory diverticulum is attached to the primitive foregut
- It grows and pinches so we have 2 separate structures: The trachea and pharynx/oesophagus
- Then the lung bud appears at the ventral wall of the foregut in the 4th week which become separated from each other
What is an abnormal development of the oesophagus?
- Oesophageal atresia (proximal blind-end part of oesophagus, most common and means it doesn’t have full development)
- Tracheoesophageal fistula (which is an abnormal connection)
When does the stomach begin to differentiate?
After 4 weeks starts to grow from the primitive gut tube
