small bowel

Question 1

Gut embryology

Answer 1

https://www.youtube.com/watch?v=vJA1A0v6Aa4

Question 2

Small intestine is derived from..?

Answer 2

Midgut. (With the exception of proximal duodenum, which is deriv from foregut)

Question 3

Meckel’s diverticulum is vestige of what?

Answer 3

Vitelline duct, which joins the yolk sac at the junction of the cranial and caudal limbs of the midgut limb

Question 4

How long is the small bowel?

Answer 4

5-10 m (longest organ in GI tract)

Question 5

Ligament of Treitz marks

Answer 5

Junction of duodenum and jejunum

Question 6

Plicae circulares

Answer 6

Transverse mucosal folds in the lumen of the small bowell- present in distal duodenum and jejunum

Question 7

Blood supply to duodenum

Answer 7

Proximal: gastroduodenal artery (off of proper hepatic artery-> branches into ant superior and post superior pancreaticoduodenal arteries).

Distal: inferior pancreaticoduodenal artery (off of SMA -> branches into ant inferior and post inferior pancreaticoduodenal arteries)

Question 8

Venous drainage of duodenum

Answer 8

Ant and post pancreaticoduodenal veins -> SMV -> splenic vein + SMV = portal vein

Question 9

Blood supply of jejunum and ileum

Answer 9

Branches of the SMA

Question 10

Summary of small bowel blood supply

Answer 10

All of small bowel is supplied by branches of the SMA except the proximal duodenum, which is supplied by branches off the celiac trunk

Question 11

Lymphatic drainage of small bowel

Answer 11

-> mesenteric nodes -> LN channels -> cisterna chyli (btw aorta and IVC) -> thoracic duct -> left subclavian vein

Question 12

Innervation to small bowel

Answer 12

Sympathetic: vagus and celiac ganglia

Parasympathetic: plexus at base of SMA

Enteric NS: myenteric plexus = Meissner plexus (base of submucosa) and Auerbach plexus (in btw inner circumferential and outer longitudinal muscle layers)

Question 13

What vessel is at risk of erosion/bleed if posterior duodenal bulb ulcer perfs?

Answer 13

Gastroduodenal artery

Question 14

How to tell between jejunum and ileum?

Answer 14

Jejunum has few arcades with loong vasa recta, while ileum has many arcades with short vasa recta

Question 15

Gastrin

Answer 15

Released in antrum. Stimulates gastric acid secretion and cell growth. Stimulated by vagus, food in Antrum, gastric distention, calcium. Inhibited by antrum pH

Question 16

Cholecystokinin (CCK)

Answer 16

Released in the duodenum. Action is gallbladder contraction, inhibit gastric emptying. Stimulated by proteins and amino acids, fat, and acid. Inhibited by trypsin and chymotrypsin.

Question 17

Secretin

Answer 17

Released in the duodenum. Action is to cause pancreas to stimulate bicarb, stimulates pepsin secretion, inhibits gastric acid secretion. Stimulated by low pH and duodenal fat. Inhibited by high duodenal pH.

Question 18

Somatostatin

Answer 18

Released from pancreas. Action is to increase small bowel absorption of water and electrolytes, inhibits GI motility, secretion/action of all GI hormones. Stimulated by intraluminal fat, catecholamines. Inhibited by acetylcholine.

Question 19

What is the clinical use of pancreatic polypeptide?

Answer 19

Only as a marker of other endocrine pancreatic tumors

Question 20

Glucagon

Answer 20

Released in small bowel/colon. Action is to stimulate glycogenolysis, lipolysis, gluconeogenesis. Stimulated by low serum glucose. Inhibited by somatostatin.

Question 21

Motilin

Answer 21

Action is to inhibit MMCs, increases gastric emptying, increases pepsin secretion. Stimulated by vagus, fat, alkaline duodenal environment. Inhibited by pancreatic polypeptide

Question 22

MMCs

Answer 22

Migrating motor complexes aka migrating myoelectric complexes. Waves of electrical activity that sweep through intestines in a regular cycle while fasting, clearing non digestible along. These waves trigger peristaltic activity. Occurs every 90-120 min while fasting and is cause of stomach “grumbling” when hungry.

Question 23

What are two things absorbed in ileum not absorbed elsewhere in small bowel?

Answer 23

Bile and b12

Question 24

What is the most important immunoglobulin in the GI tract?

Answer 24

IgA

Question 25

Age distribution of Crohns

Answer 25

Bi modal, 15-40 and 80 years

Question 26

Risk factors for CD

Answer 26

Smoking, white race, northern location, Jewish, family history

Question 27

Neoplasia of the small bowel can cause colicky abdominal pain by what mechanism?

Answer 27

Intermittent intussusception

Question 28

Peutz-Jeghers syndrome

Answer 28

Hamartamatous polyps. Pigmented spots on lips.

Question 29

Gardner syndrome

Answer 29

Colonic adenomas with increased risk of colon cancer. Autosomal dominant. Tumors: osteomas of skull, epidermoid cysts, fibroids, thyroid tumors.

Question 30

What other types of benign tumors can occur in small bowel?

Answer 30

Hemangioma, fibroma, lipoma, leiomyoma

Question 31

Two most common types of small bowel malignancies

Answer 31

Adenocarcinoma and carcinoid

Question 32

Most common location for carcinoid tumor in the small bowel

Answer 32

Ileum

Question 33

Carcinoid syndrome caused by what hormone excess?

Answer 33

Serotonin, tryptophan, or bradykinin. Can end up having pellagra because using so much niacin to make serotonin/tryptophan.

Question 34

Other types of small bowel malignant tumors

Answer 34

Lymphoma, sarcoma, neuroendocrine, mets

Question 35

Risk factors for lymphoma of small bowel

Answer 35

Celiac disease, immunosuppresion, autoimmune disease

Question 36

Where is the most common site of carcinoid tumor overall?

Answer 36

Appendix (better prognosis)

Question 37

What is the cell of origin in carcinoid tumors?

Answer 37

Enterochromaffin cell

Question 38

Carcinoid syndrome usually occurs with appendiceal and small intestine carcinoid tumors only after what event?

Answer 38

Metastasis to the liver. This is because tumor is producing amines and peptides outside of the portovenous circulation.

Question 39

How to treat fistula of small bowel

Answer 39

Consider somatostatin for high output fistulae, to decrease loss of fluids and electrolytes. IV antibiotics and bowel rest. If six weeks pass with no improvement resect tract and consider proximal ostomy if abscess found.

Question 40

Small bowel obstruction (SBO) definition

Answer 40

Cessation, impairment, or reversal of transit of intestinal contents secondary to mechanical OR functional cause

Question 41

Open loop SBO

Answer 41

Flow is blocked but proximal decompression possible

Question 42

Closed loop obstruction

Answer 42

Inflow and outflow both blocked. Seen with incarcerated hernia, torsion, adhesions, volvulus. Requires emergent surgery

Question 43

Most common causes of SBO

Answer 43

Extrinsic causes: adhesions, hernias, cancer

Question 44

Other mechanical causes of SBO

Answer 44

Foreign body, gallstone ileus, intussusception. Crohns, lymphoma, radiation enteritis, abscess.

Question 45

Functional causes of SBO (paralytic ileus)

Answer 45

Hypokalemia, peritonitis, ischemia, meds (opiates, anticholinergics), hemoperitoneum, retroperitoneal hematoma, postoperative, massive burn.

Question 46

Management of SBO if patient is stable or has partial obstruction

Answer 46

IVF, NPO, NG tube decompression. Manage electrolytes and pain

Question 47

Diagnosis and treatment of intussusception

Answer 47

Barium enema