L6 Embryology 1

Question 1

Where does the primitive gut tube extend from and to?

Answer 1

From the oropharyngeal membrane to the cloacal membrane.

Question 2

How can the primitive gut tube be divided?

Answer 2

Foregut - Mouth to the first part of the duodenum

Midgut - 2nd part of the duodenum to 2/3rds into the transverse colon. The midgut is continuous with the yolk sac at the vitalise duct.

Hindgut - Distal 1/3rd of the transverse colon to the superior 2/3rds of the rectum.

Question 3

Where is the inner epithelial lining derived from?

Answer 3

Endoderm

Question 4

Where is the smooth muscles and connective tissue derived from?

Answer 4

Visceral mesoderm

Question 5

What is the viscera and parietal peritoneum derived from?

Answer 5

Mesoderm

Question 6

What is the primitive gut tube suspend from the posterior abdominal wall by?

Answer 6

Dorsal mesentery

Question 7

What is a mesentery?

Answer 7

Double layer of peritoneum. This is where visceral and parietal peritoneum meet.

Question 8

What is an intraperitoneal organ?

Answer 8

An organ that is invested in the peritoneum.

Question 9

What is a retroperitoneal organ?

Answer 9

An organ whose anterior surface only is covered by peritoneum.

Question 10

Where does the dorsal mesentery extend to?

Answer 10

From the lower oesophagus to the cloacal.

Question 11

Where does the ventral mesentery lie?

Answer 11

From the lower oesophagus to the first part fo the duodenum. This goes onto form the lesser momentum and the falciform ligament (umbilical vein). The ventral mesentery is only found at the level of the foregut.

Question 12

What is the purpose of a mesentery?

Answer 12

Acts as a root for vessels, nerves and lymphatics to travel through. It also helps to connect an organ to the dorsal surface.

Question 13

Which vitelliane arteries give rise to the arteries of the GI tract?

Answer 13

Celiac artery - supplies the foregut

Superior mesenteric artery = supplies the midgut

inferior mesenteric artery = supplies the handout

Question 14

How is the definitive gut lumen formed?

Answer 14

We start of with a hollow tube. The cells divide so much it becomes solid. Through apoptosis, there is gaps. The gaps fuse to form a hollow tube again. When the cells proliferate they specialise also. Through apoptosis we are left with an area of specialised cells. E.g. in the stomach there is specialised cells that form acid, these cells will not be found in the SI.

Starts in week 6, and a hollow tube again in week 9.

Question 15

How can abnormal recanalisation of the gut tube form?

Answer 15

Abnormal apoptosis can cause an extra part of gut tube, a duplication cyst. This can cause problem if food gets trapped and bacteria can respire leading to infection. If it is not complete or sufficient, this can lead to a stenosis of the gut tube. We can also have atresia due to incomplete apoptosis. These are most commonly in the ileum and the duodenum. This leads to disruptions or intrusssception, the bowel folds inside each other. This can lead to obstruction.

Question 16

What is polyhydramnios?

Answer 16

Oesophageal atresias mean that the foetus cannot swallow amniotic fluid and return t to the mother through placental circulation. This leads to a build up of fluid and so an enlarged pregnancy bump.

Question 17

What is a congenital hiatal hernia?

Answer 17

Failure of the oesophagus to elongate.

Question 18

When does the stomach appear?

Answer 18

Week 4

Question 19

When does rotation of the stomach occur?

Answer 19

Week 7-8

Question 20

What is the effect of rotation of the stomach?

Answer 20

There is differential growth of the stomach (faces caudally) forming a greater curvature and a lesser curvature (facing cranially). The stomach rotates 90 degrees clockwise. This means the liver is pushed to the right side and the spleen to the left hand side. There is a left and a right space (sac). With rotation of the stomach, the right and left become ventral and dorsal sac in relation to the stomach. Eventually it will lead to a greater space in front to the stomach called the greater sac, and a smaller one behind known as a lesser sac.

Question 21

What is the epiploic foremen?

Answer 21

A continuation between the greater and lesser sac.

Question 22

How is the greater omenutm formed?

Answer 22

The dorsal mesentery grows rapidly. This attaches to the greater curvature. It folds back on itself. x

Question 23

How many layers of peritoneum make up the greater omentum?

Answer 23

The dorsal mesentery grows rapidly. This attaches to the greater curvature. It folds back on itself. A mesentery is 2 layers of peritoneum. When it folds back on itself there are 2 layers in front and 2 behind. This eventually folds. The greater omentum attaching to the posterior wall is therefore 4 layers of peritoneum.

Question 24

What is a congenital pyloric stenosis?

Answer 24

The muscles of the pyloric sphincter can be thickened. This leads to a palpable pyloric mass on the anterior wall. Signs are projectile vomiting and a visible peristaltic movement.

Question 25

What is heterotrophic gastric tissue?

Answer 25

This is cells in the stomach end up else where. They can end up in the tongue or small intestine. Problems arise when the cells secrete acid. This can cause irritation of the epithelial lining. This can lead to strictures and sacring or rupture of the gut wall.

Question 26

How is the duodenum formed?

Answer 26

The stomach continues with the duodenum. When the stomach rotates, the duodenum does also. The second part of the duodenum forms a C shape and is dragged to the right side. It pushes it so far, the dorsal mesentery disintegrates. If the dorsal mesentery disintegrates it only have a covering on the anterior aspect. It only has a peritoneum on its dorsal surface. It becomes retroperitoneum as it doesn’t have peritoneum covering it around the whole of the duodenum. It is secondarily retroperitoneum as at some point it was intraperitoneal.

Question 27

Where does skeletal muscle around the oesophagus derived from?

Answer 27

Paraxial mesoderm

Question 28

What develops in the ventral mesentery?

Answer 28

The liver

Question 29

What does the ventral mesentery split into?

Answer 29

The mesentery is split into two: that goes from the liver to the anterior wall falciform ligament and the other that goes to the stomach to the liver less omentum.