Intestines

Question 1

What are the four parts of the duodenum?

Answer 1

• 1st (superior): from the pylorus (duodenal cap), goes right to the 2nd part
• 2nd (descending): the descending part, contains the duodenal papillae (this is where the foregut becomes the midgut)
• 3rd (inferior): from 2nd, it turns left into the 4th part
• 4th (ascending): ascends almost to the height of the 1st part before becoming the duodeno-jejunal junction (DJ flexure)

Question 2

What connects the jejunum and ileum to the posterior abdominal wall?

Answer 2

• the root of the mesentery

Question 3

How can you tell the jejunum and the ileum apart?

Answer 3

• jejunum: 1 vascular arcade with long vasa recta; many ineternal circular folds (plicae circularis); no palpable notches
• ileum: multiple vascular arcades with short vasa recta; few plicae circularis (so it’s smoother); more creeping fat; contains palpable notches (Peyer’s patches)

Question 4

What are the parts of the large intestine?

Answer 4

• ileocecal valve/junction into the cecum w/ appendix
• ascending colon, transverse colon, descending colon, sigmoid colon (the midgut becomes the hindgut at the splenic flexure b/w transverse and descending colons)
• rectum
• anal canal

Question 5

What is the mesoappendix? What does it contain?

Answer 5

• mesoappendix is the appendix’s own little mesentery

- it contains the appendicular artery

Question 6

What causes the colon’s haustra?

Answer 6

• the taeniae coli (the banded outer longitudinal layer of smooth muscle) because these are shorter than the underlying continuous circular layer

Question 7

Which major arteries supply the foregut, midgut, and hindgut?

Answer 7

• foregut: celiac trunk (esophagus to 2nd part of duodenum)
• midgut: superior mesenteric artery (2nd part of duodenum to splenic (left colic) flexure)
• hindgut: inferior mesenteric artery (splenic flexure to anus)

Question 8

Explain the blood supply to the midgut.

Answer 8

• (major artery: superior mesenteric artery)
• SMA gives off many small jejunal and ileal arteries
• gives off the ileocolic artery to supply the cecum, appendix, and proximal ascending colon
• gives off the right and middle colic arteries (right supplies ascending, middle supplies transverse)
• all of these branches join to form the marginal artery (of Drummond), which supplies nearly all of the colon

Question 9

Explain the blood supply to the hindgut.

Answer 9

• (major artery: inferior mesenteric artery)
• IMA gives off the left colic artery to the supply the descending colon
• gives off 2 or 3 sigmoid arteries to supply the sigmoid colon
• gives off 1 or 2 superior rectal arteries to help supply the rectum
• (the left colic artery helps form the marginal artery (of Drummon), which supplies nearly all of the colon

Question 10

Is venous return to the IVC or to the hepatic portal system?

Answer 10

• to the hepatic portal system!
• (note that the lower anorectal canal can drain either into the portal system via the superior rectal vein OR into the IVC via the inferior and middle rectal veins which drain into the internal iliac veins –> portosystemic shunts!)

Question 11

Which veins join to form the portal vein?

Answer 11

• the splenic and the superior mesenteric veins

- the inferior mesenteric vein also joins to form the portal vein (it usually joins with the splenic vein to do so)

Question 12

Lymphatic Drainage

Answer 12

• for the upper small intestine (and stomach) we have the cisterna chyli, which drains into the thoracic duct (which drains into the venous vessels in the neck)
• for the rest of the small intestine and the colon, lymph nodes are located along the arterial path
• for above the anorectal pectinate line: drainage is upwards and lateral to either the superior rectal nodes (to inferior mesenteric nodes) or to the middle rectal nodes (to external iliac nodes)
• for below the pectinate line: drainage is lateral to the superficial inguinal nodes (to internal iliac nodes)