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GI > Session 2: Development of the Gastrointestinal System I > Flashcards

Session 2: Development of the Gastrointestinal System I Flashcards

1
Q

Explain the embryonic folding of the gut tube.

A

In the 4th week the embryo folds laterally in order to make the primitive gut to become tubular. It also folds craniocaudally in order to create cranial and caudal pockets from yolk sac endoderm. This is the beginning of formation of the foregut and hindgut.

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2
Q

Explain what the gut tube is and its contents.

A

It is an endoderm lined tube that runs the length of the body. It has blind pouches at the head (cranial) and tail (caudal) ends. Its opening is at the umbilicus and it is covered by splanchnic mesoderm.

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3
Q

The gut has three divisions; foregut, midgut and hindgut. What do each begin as?

A

Foregut and hindgut begin as blind diverticula from the craniocaudal folding. The midgut begin in the middle with an opening at first as it is continuous with the yolk sac.

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4
Q

Derivatives of the foregut.

A

Oesophagus Stomach Pancreas, liver and gall bladder. Duodenum proximal to the entrance of the bile duct.

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5
Q

Derivatives of the midgut.

A

Duodenum distal to the entrance of the bile duct. Jejunum Ileum Caecum Ascending colon Proximal 2/3 of transverse colon

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6
Q

Derivatives of the hindgut.

A

Distal 1/3 of the transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of bladder and urethra

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7
Q

Arterial blood supply of the foregut.

A

Coeliac trunk

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8
Q

Arterial blood supply of the midgut.

A

Superior mesenteric artery

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9
Q

Arterial blood supply of the hindgut.

A

Inferior mesenteric artery

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10
Q

There are some exceptions of where the arterial blood supply somewhat differ from the general rule of the arterial blood supply being divided into these three arterial supplies. What are the exceptions?

A

Duodenum prejunction (with the bile duct) is supplied by the coeliac trunk and postjunction it is supplied by the superior mesenteric artery. The superior head of pancreas is supplied by the coeliac trunk and the inferior head is supplied by the superior mesenteric artery.

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11
Q

What are the mesenteries?

A

Double layer of peritoneum suspending the gut tube from the abdominal wall.

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12
Q

Purpose of the mesenteries.

A

Allow a conduit for blood and nerve supply. Allow mobility where it is needed.

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13
Q
A
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14
Q

What will the splanchnic mesoderm become?

A

The mesentery and the visceral peritoneum.

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15
Q

What will the somatic mesoderm become?

A

The parietal peritoneum.

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16
Q

What differents types of mesentery are there?

A

Dorsal and ventral mesentery.

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17
Q

Where can you find the dorsal mesentery?

A

Dorsal means posterior in embryology and it will suspend the entire gut tube from the dorsal body wall.

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18
Q

Where can you find the ventral mesentery?

A

Ventral means anterior in embryology and it can be found only in the region of the foregut.

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19
Q

What other purpose than mobility and blood supply does the dorsal and ventral mesenteries have in the foregut?

A

They divide the region of the foregut into two cavities called the left and right sacs.

20
Q

What other purpose than mobility and blood supply do the mesenteries have in the midgut and hindgut?

A

The ventral mesentery does not have any function here as it only goes as far as the foregut.

However the dorsal mesentery can be found here. The dorsal mesentery divides the region of the midgut and hindgut into a cavity as well.

21
Q

What are the cavities called which the mesenteries divide the foregut into?

A

The left and right sacs.

22
Q

Which sac can be found in the midgut and hindgut?

A

The left sac.

23
Q

What does the right sac contribute to?

A

The right sac is much smaller as it can only be found in the foregut. It becomes the lesser sac. It will lie behind the stomach.

24
Q

What does the left sac contribute to?

A

The left sac contributes to the greater sac.

25
Q
A
26
Q

What is the greater omentum and where can it be found?

A

It is formed from the dorsal mesentery and can be found attached to the greater curvature of the stomach and is the first structure seen when the abdominal cavity is opened anteriorly.

27
Q

What is the lesser omentum and where can it be found?

A

It is formed from the ventral mesentery which means it will only be found in the foregut.

It conducts the portal triad for the liver and connects the lesser curvature of the stomach to the liver.

28
Q

Where does the development of the stomach begin?

A

In the foregut.

The developing stomach is attached to the body walls by the dorsal and ventral mesenteries.

29
Q

Where can you find the vagus nerves in relation to the stomach?

A

The left vagus nerve flanks the left side of the stomach.

The right vagus nerve flanks the right side of the stomach.

30
Q

What causes the greater and lesser curvatures of the stomach?

A

It is simply that the dorsal wall of the stomach grows faster than the ventral wall.

31
Q

What is the next step in the development of the stomach? (At week 7)

A

The stomach starts to rotate 90 degrees upon its longitudinal axis.

32
Q

What are the consequences of the 90 degrees longitudinal rotation of the stomach?

A

A space is formed behind the stomach which is the lesser sac. Aka the right sac becomes the lesser sac.

This also causes the greater curvature to face the left side of the body and the lesser curvature will face the right side.

The left vagus nerve is now located on the anterior side of the stomach and the right vagus nerve is located on the posterior side. The anatomical positions of the vagus nerves makes them being renamed to anterior vagal trunk and posterior vagal trunk.

33
Q

The stomach and duodenum rotate once more. How do they rotate?

A

About its ventrodorsal axis which pulls the end of the stomach upwards. This also causes the duodenum to be pulled into a C-shaped position.

This is the final position of the stomach and duodenum.

34
Q

What is a peritoneal reflection?

A

A change in direction of the peritoneum.

This can be found when parietal peritoneum goes to mesentery.

From when mesentery goes to visceral peritoneum.

35
Q

What are retroperitoneal structures?

A

Structures that are not suspended within the abdominal cavity and were never in the peritoneal cavity + never had a mesentery.

36
Q

What are secondarily retroperitoneal structures?

A

They began their development invested in peritoneum, they had a mesentery but with successive growth and development the mesentery was lost through fusion at the posterior abdominal wall.

37
Q

Where does the foregut extends from prior to the 4th week?

A

From the lung bud to the liver bud.

38
Q

What happens at the 4th week of development to the foregut?

A

A respiratory diverticulum forms in the ventral wall of the foregut at the junction with the pharyngeal gut.

Now between the foregut and the respiratory diverticulum a septum will be formed called the tracheoesophageal septum.

39
Q

What is the consequence of the formation of the diverticulum and the septum?

A

It separates the developing GI tract from the developing respiratory tract.

40
Q

Give some examples of abnormal development of the tracheoesophageal septum.

A

There might be a proximal blind end oesophagus and a tracheaoesophageal fistula.

There may be two tracheoesophageal fistulas.

There may be two blind ends, one proximal and one distal.

41
Q

Where does the liver and biliary system develop?

A

In the ventral mesentery (as it will be found to the right of the stomach)

42
Q

Where does the pancreas develop?

A

The uncinate process and the inferior head develops ventrally.

The superior head, neck, body and tail develop dorsally.

This explains why the blood supply differs.

43
Q
A
44
Q

Is the duodenum a peritoneal structure, retroperitoneal or secondarily retroperitoneal?

A

It is secondarily retroperitoneal.

This is because the rotation of the stomach pushes the duodenum to the right and then against the posterior abdominal wall.

45
Q

Give another example of a secondarily retroperitoneal structure of the foregut.

A

The pancreas.

46
Q

The greater and lesser sacs communicate via an opening. What is it called and where can it be found?

A

It is found near the hilum of the liver and is called foramen of Winslow, epiploic foramen or omentum foramen.

GI (30 decks)

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