Embryology of the midgut & hindgut

Question 1

What is the blood supply for the midgut?

Answer 1

superior mesenteric artery

Question 2

What is the blood supply of the hindgut?

Answer 2

inferior mesenteric artery

Question 3

What are the two limbs of the midgut loop and what do they develop into?

Answer 3

1. cranial limb –> small intestine

2. caudal limb –> large intestine

Question 4

What is a physiological midgut hernia?

Answer 4

During development there is not enough room in the abdomen for the rapidly growing midgut

• -> midgut projects into proximal part of umbilical cord
• -> intestines return to abdomen during 10th week of development

Question 5

What is the embryonic form of the cecum and appendix?

Answer 5

The cecal diverticulum

Question 6

name some GI structures that have mesentery

Answer 6

ileum
jejunum
appendix
transverse colon
sigmoid colon

Question 7

Name some secondary retroperitoneal organs

Answer 7

Pancreas, most of the duodenum, descending colon, ascending colon

Question 8

What are the most common causes of abnormalities of the midgut?

Answer 8

Anomalies of gut rotation

Question 9

What is the name for having all your insides completely reversed (ie. mirror image to everyone else)

Answer 9

Situs inversus

–> as a result of ciliary dyskinesia

Question 10

What is an omphalocele?

Answer 10

Failure of the intestinal loops to return to the abdomen, so they protrude outside umbilicus (without skin covering).
The loops are instead surrounded with membranous sac.

Question 11

What is an umbilical hernia?

Answer 11

After retreating to the abdomen, the intestines herniate through an imperfectly closed umbilicus. Protrusion is still covered by skin.

Question 12

What are the clues for identifying Meckel’s Diverticulum?

Answer 12

• 2 inches long
• 2 feet from the ileocecal junction
• 2% population prevalence

Question 13

How is Meckel’s diverticulum formed?

Answer 13

when the proximal portion of the yolk sac remains

Question 14

What is the clinical significance of Meckel’s Diverticulum?

Answer 14

Sometimes becomes inflamed and causes symptoms that mimic appendicitis.

• -> wall may contain small patches of gastric/pancreatic tissue.
• ->gastric mucosa produces acid and may cause bleeding

Question 15

What is the cloaca?

Answer 15

The terminal dilated portion of the hindgut.

Contacts the surface ectoderm at the cloaca membrane.

Question 16

What is the cloaca membrane made up of?

Answer 16

Endoderm of cloaca and ectoderm of proctodeum or anal pit.

Question 17

The cloaca is divided into ventral and dorsal parts by what?

Answer 17

The urorectal septum

Question 18

What is the ventral portion of the cloaca called?

Answer 18

Urogenitial sinus

Question 19

What makes up the dorsal portion of the cloaca?

Answer 19

Rectum and cranial part of the anal canal

Question 20

The urorectal septum divides the cloacal sphincter into what?

Answer 20

Anterior portion –> muscles covering external genitalia erectile tissues (bulbospongiosus and ischiocavernosus muscles)
Posterior portion –> external anal sphincter

Question 21

What happens if the anal membrane is ruptured?

Answer 21

The distal part of the digestive tract (anal canal) communicates with the amniotic cavity.

Question 22

What is the embryonic origin of the anal canal?

Answer 22

Upper 2/3: from hindgut (endoderm)

Lower 1/3: from proctodeum (ectoderm)

Question 23

If there is a cancer in the anal canal, when will it cause pain?

Answer 23

Only if it invades the lower 1/3 of the anal canal.