small bowel Flashcards
Gut embryology
https://www.youtube.com/watch?v=vJA1A0v6Aa4
Small intestine is derived from..?
Midgut. (With the exception of proximal duodenum, which is deriv from foregut)
Meckel’s diverticulum is vestige of what?
Vitelline duct, which joins the yolk sac at the junction of the cranial and caudal limbs of the midgut limb
How long is the small bowel?
5-10 m (longest organ in GI tract)
Ligament of Treitz marks
Junction of duodenum and jejunum
Plicae circulares
Transverse mucosal folds in the lumen of the small bowell- present in distal duodenum and jejunum
Blood supply to duodenum
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)
Venous drainage of duodenum
Ant and post pancreaticoduodenal veins -> SMV -> splenic vein + SMV = portal vein
Blood supply of jejunum and ileum
Branches of the SMA
Summary of small bowel blood supply
All of small bowel is supplied by branches of the SMA except the proximal duodenum, which is supplied by branches off the celiac trunk
Lymphatic drainage of small bowel
-> mesenteric nodes -> LN channels -> cisterna chyli (btw aorta and IVC) -> thoracic duct -> left subclavian vein
Innervation to small bowel
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)
What vessel is at risk of erosion/bleed if posterior duodenal bulb ulcer perfs?
Gastroduodenal artery
How to tell between jejunum and ileum?
Jejunum has few arcades with loong vasa recta, while ileum has many arcades with short vasa recta
Gastrin
Released in antrum. Stimulates gastric acid secretion and cell growth. Stimulated by vagus, food in Antrum, gastric distention, calcium. Inhibited by antrum pH
Cholecystokinin (CCK)
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.
Secretin
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.
Somatostatin
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.
What is the clinical use of pancreatic polypeptide?
Only as a marker of other endocrine pancreatic tumors
Glucagon
Released in small bowel/colon. Action is to stimulate glycogenolysis, lipolysis, gluconeogenesis. Stimulated by low serum glucose. Inhibited by somatostatin.
Motilin
Action is to inhibit MMCs, increases gastric emptying, increases pepsin secretion. Stimulated by vagus, fat, alkaline duodenal environment. Inhibited by pancreatic polypeptide
MMCs
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.
What are two things absorbed in ileum not absorbed elsewhere in small bowel?
Bile and b12
What is the most important immunoglobulin in the GI tract?
IgA
Age distribution of Crohns
Bi modal, 15-40 and 80 years
Risk factors for CD
Smoking, white race, northern location, Jewish, family history
Neoplasia of the small bowel can cause colicky abdominal pain by what mechanism?
Intermittent intussusception
Peutz-Jeghers syndrome
Hamartamatous polyps. Pigmented spots on lips.
Gardner syndrome
Colonic adenomas with increased risk of colon cancer. Autosomal dominant. Tumors: osteomas of skull, epidermoid cysts, fibroids, thyroid tumors.
What other types of benign tumors can occur in small bowel?
Hemangioma, fibroma, lipoma, leiomyoma
Two most common types of small bowel malignancies
Adenocarcinoma and carcinoid
Most common location for carcinoid tumor in the small bowel
Ileum
Carcinoid syndrome caused by what hormone excess?
Serotonin, tryptophan, or bradykinin. Can end up having pellagra because using so much niacin to make serotonin/tryptophan.
Other types of small bowel malignant tumors
Lymphoma, sarcoma, neuroendocrine, mets
Risk factors for lymphoma of small bowel
Celiac disease, immunosuppresion, autoimmune disease
Where is the most common site of carcinoid tumor overall?
Appendix (better prognosis)
What is the cell of origin in carcinoid tumors?
Enterochromaffin cell
Carcinoid syndrome usually occurs with appendiceal and small intestine carcinoid tumors only after what event?
Metastasis to the liver. This is because tumor is producing amines and peptides outside of the portovenous circulation.
How to treat fistula of small bowel
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.
Small bowel obstruction (SBO) definition
Cessation, impairment, or reversal of transit of intestinal contents secondary to mechanical OR functional cause
Open loop SBO
Flow is blocked but proximal decompression possible
Closed loop obstruction
Inflow and outflow both blocked. Seen with incarcerated hernia, torsion, adhesions, volvulus. Requires emergent surgery
Most common causes of SBO
Extrinsic causes: adhesions, hernias, cancer
Other mechanical causes of SBO
Foreign body, gallstone ileus, intussusception. Crohns, lymphoma, radiation enteritis, abscess.
Functional causes of SBO (paralytic ileus)
Hypokalemia, peritonitis, ischemia, meds (opiates, anticholinergics), hemoperitoneum, retroperitoneal hematoma, postoperative, massive burn.
Management of SBO if patient is stable or has partial obstruction
IVF, NPO, NG tube decompression. Manage electrolytes and pain
Diagnosis and treatment of intussusception
Barium enema
