– Small Bowel

Small intestine – nutrient and water absorption

Large intestine – water absorption

Duodenum

• Bulb (1st portion) – 90% of ulcers here

• Descending (2nd) – contains ampulla of Vater (duct of Wirsung) and duct of Santorini

• Transverse (3rd)

• Ascending (4th)

• Descending and transverse portions are retroperitoneal

• 3rd and 4th portions – transition point at the acute angle between the aorta (posterior) and SMA (anterior)

• Vascular supply is superior (off gastroduodenal artery) and inferior (off SMA) pancreaticoduodenal arteries

• Both have anterior and posterior branches

• Many communications between these arteries

Jejunum

• 100 cm long; long vasa recta, circular muscle folds

• Is the maximum site of all absorption except for B₁₂ (terminal ileum), bile acids (ileum – non-conjugated; terminal ileum – conjugated), iron (duodenum), and folate (terminal ileum)

• 95% of NaCl absorbed and 90% of water absorbed in jejunum

• Vascular supply – SMA

Ileum – 150 cm long; short vasa recta, flat

• Vascular supply – SMA

Intestinal brush border – maltase, sucrase, limit dextrinase, lactase

Normal sizes – small bowel/transverse colon/cecum → 3/6/9 cm

SMA eventually branches into the ileocolic artery

Cell types

• Absorptive cells

• Goblet cells (mucin secretion)

• Paneth cells (secretory granules, enzymes)

• Enterochromaffin cells (APUD, 5-hydoxytryptamine release, carcinoid precursor)

• Brunner’s glands (alkaline solution)

• Peyer’s patches (lymphoid tissue); increased in the ileum

• M cells – antigen-presenting cells in intestinal wall

IgA – released into gut; also in mother’s milk

Fe – small bowel has both heme and Fe transporters

Migrating motor complex (gut motility)

• Phase I – rest

• Phase II – acceleration and gallbladder contraction

• Phase III – peristalsis

• Phase IV – deceleration

• Motilin is most important hormone in migrating motor complex (acts on phase III)

Bile salts (acids)

• 95% of bile salts are reabsorbed

• 50% passive absorption (non-conjugated bile salts) – 45% ileum, 5% colon

• 50% active resorption (conjugated bile salts) in terminal ileum (Na/K ATPase); conjugated bile salts are absorbed only in the terminal ileum

• Gallstones form after terminal ileum resection from malabsorption of bile salts

SHORT-GUT SYNDROME

Diagnosis is made on symptoms, not length of bowel

Symptoms: diarrhea, steatorrhea, weight loss, nutritional deficiency

Lose fat, B₁₂, electrolytes, water

Sudan red stain – checks for fecal fat

Schilling test – checks for B₁₂ absorption (radiolabeled B₁₂ in urine)

Probably need at least 75 cm to survive off TPN; 50 cm with competent ileocecal valve

Tx: restrict fat, PPI to reduce acid, Lomotil (diphenoxylate and atropine)

CAUSES OF STEATORRHEA

Gastric hypersecretion of acid → ↓ pH → ↑ intestinal motility; interferes with fat absorption

Interruption of bile salt resorption (eg terminal ileum resection) interferes with micelle formation and fat absorption

Tx: control diarrhea (Lomotil); ↓ oral intake, especially fats; Pancrease, PPI

NONHEALING FISTULA

“FRIENDS” – mnemonic for causes of nonhealing fistula: foreign body, radiation, inflammatory bowel disease, epithelialization, neoplasm, distal obstruction, sepsis/infection

High-output fistulas are more likely with proximal bowel (duodenum or proximal jejunum) and are less likely to close with conservative management

Colonic fistulas are more likely to close than those in small bowel

Patients with persistent fever – need to check for abscess (fistulogram, abdominal CT, upper GI with small bowel follow-through)

Most fistulas are iatrogenic and treated conservatively 1st → NPO, TPN, skin protection (stoma appliance), octreotide

Majority close spontaneously without surgery

Surgical options: resect bowel segment containing fistula and perform primary anastomosis

OBSTRUCTION

Without previous surgery (most common)

• Small bowel – hernia

• Large bowel – cancer

With previous surgery (most common)

• Small bowel – adhesions

• Large bowel – cancer

Symptoms: nausea and vomiting, crampy abdominal pain, failure to pass gas or stool

Abdominal x-ray: air–fluid level, distended loops of small bowel, distal decompression

3rd spacing of fluid into bowel lumen occurs – need aggressive fluid resuscitation

Air with bowel obstruction – from swallowed nitrogen

Tx: bowel rest, NG tube, IV fluids → cures 80% of partial SBO, 40% of complete SBO

Surgical indications: progressing pain, peritoneal signs, fever, increasing WBCs, (all signs of strangulation or perforation), or failure to resolve

GALLSTONE ILEUS

Small bowel obstruction from gallstone usually in the terminal ileum

Classically see air in the biliary tree in a patient with small bowel obstruction

Caused by a fistula between the gallbladder and second portion of duodenum

Tx: remove stone from terminal ileum

• Can leave gallbladder and fistula if patient too sick

• If not too sick, perform cholecystectomy and close duodenum

MECKEL’S DIVERTICULUM

2 ft from ileocecal valve; 2% of population; usually presents in 1st 2 years of life with bleeding; is a true diverticulum

Caused by failure of closure of the omphalomesenteric duct

Accounts for 50% of all painless lower GI bleeds in children < 2 years

Pancreas tissue – most common tissue found in Meckel’s (can cause diverticulitis)

Gastric mucosa – most likely to be symptomatic (bleeding most common)

Obstruction – most common presentation in adults

Incidental → usually not removed unless gastric mucosa suspected (diverticulum feels thick) or has a very narrow neck

Dx: can get a Meckel’s scan (⁹⁹Tc) if having trouble localizing (mucosa lights up)

Tx: diverticulectomy for uncomplicated diverticulitis or bleeding

• Need segmental resection for complicated diverticulitis (eg perforation), neck > ⅓ the diameter of the normal bowel lumen, or if diverticulitis involves the base

DUODENAL DIVERTICULA

Need to rule out gallbladder-duodenal fistula

Observe unless perforated, bleeding, causing obstruction, or highly symptomatic

Frequency of diverticula: duodenal > jejunal > ileal

Tx: segmental resection if symptomatic

• If juxta-ampullary usually can’t get resection and need choledochojejunostomy for biliary or ERCP with stent for pancreatitis symptoms (avoid Whipple here)

CROHN’S DISEASE

Inflammatory bowel disease causing intermittent abdominal pain, diarrhea, and weight loss; can also cause bowel obstructions and fistulas

15–35 years old at 1st presentation; in Ashkenazi Jews

Extraintestinal manifestations – arthritis, arthralgias, pyoderma gangrenosum, erythema nodosum, ocular diseases, growth failure, megaloblastic anemia from folate and vitamin B₁₂ malabsorption