chapter 35: small bowel. Flashcards
intestine: nutrient and water absorption
small intestine
intestine: water absorption
large intestine
portions of the 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)
portions of the duodenum that are retroperitoneal
descending and transverse portions
transition point of the 3rd and 4th portions of the duodenum
acute angle between the aorta (posterior) and SMA (anterior)
vascular supply duodenum
superior (off gastroduodenal artery) and inferior (off SMA) pancreaticoduodenal arteries
- both have anterior and posterior branches
- many communications between these arteries
100 cm long; long vasa recta, circular muscle folds
- absorbs 95% NaCl and 90% water
- vascular supply: SMA
Jejunum
maximum site of all absorption except for b12 (terminal ileum), bile acids (ileum - non conjugated; terminal ileum - conjugated), iron (duodenum) and folate (terminal ileum)
jejunum
150 cm long, short vasa recta, flat
- vascular supply: sma
ileum
what is absorbed at the 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 of the small intestine
absorptive cells, goblet cells (mucin secretion), paneth cells (secretory granules, enzymes), enterochromaffin cells, runner’s glands, peyer’s patches, m cells
What do goblet cells secrete?
mucin secretion
What do paneth cells secrete?
secretory granules, enzymes
What do enterochromaffin cells secrete?
APUD, 5-hydroxytryptamine release, carcinoid precursor
What do brunner’s cells secrete?
alkaline solution
What do M cells secrete?
antigen-presenting cells in intestinal wall
released into the gut; also in mother’s milk
IgA
small bowel has both heme and Fe transporters
Fe
where is iron absorbed?
duodenum
where is folate absorbed?
terminal ileum
where is b12 absorbed?
terminal ileum
where are bile acids absorbed?
- ileum: non conjugated
- terminal ileum: conjugated
what are the phases of migrating motor complex (gut motility)?
phase 1: rest
2: acceleration and gallbladder contraction
3: peristalsis
4: deceleration
Most important hormone in migrating motor complex (Acts on phase 3)
motilin
percent of bile salts reabsorbed
95%
how are bile salts reabsorbed?
- 50% passive absorption (non-conjguated bile salts) - 45% ileum, 5%
- 50% active resorption (conjugated bile salts) in terminal ileum (Na/K ATPase); conjugated bile salts are absorbed only in the terminal ileum
When do gallstones form?
gallstones form after terminal ileum resection from malabsorption of bile salts
how is diagnosis of short-gut syndrome made?
symptoms; not length of bowel
diarrhea, steatorrhea, weight loss, nutritional deficiency
- lose fat, B12, electrolytes, water
short-gut syndrome
stains: checks for fecal fat
sudan red stain
test: checks for b12 absorption (radiolabeled b12 in urine)
schilling test
how much bowel do you need to survive off TPN?
75 cm to survive off TPN; 50 cm with competent ileocecal valve
Tx: short gut syndrome
restrict fat, ppi to reduce acid, lomotil (diphenoxylate and atropine)
causes of steatorrhea
- gastric hyper secretion of acid
- interruption of bile salt resorption
how does gastric hyper secretion of acid cause steatorrhea?
decreased pH-> increased intestinal motility; interferes with fat absorption
how does interruption of bile salt resorption cause steatorrhea?
(eg terminal ileum resection) interferes with micelle formation and fat absorption
Tx: steatorrhea
control diarrhea (lomotil); decrease oral intake, especially fats, pancreas, ppi
causes of non healing fistulas
FRIENDS: fistulas, radiation, inflammatory bowel disease, epithelialization, neoplasm, distal obstruction, sepsis/infection
characteristics of high-output fistulas
- more likely with proximal bowel (duodenum or proximal jejunum)
- less likely to close with conservative management
colonic fistulas vs small bowel
- which are more likely to close?
colonic fistulas are more likely to close than those in small bowel
nonhealing fistula: patients with persistent fever
need to check for abscess (fistulogram, abdominal CT, upper GI with small bowel follow through)
treatment: fistulas
most fistulas are iatrogenic and treated conservatively first: NPO, TPN, skin protection (stoma appliance), octreotide
how do most non healing fistulas close?
majority close spontaneously without surgery
surgical options of non healing fistulas
resect bowel segment containing fistula and perform primary anastomosis
MCC obstruction without previous surgery
Small bowel: hernia
Large bowel: cancer
MCC obstruction with previous surgery
Small bowel: adhesions
Large bowel: cancer
- pain: intermittent, intense, colicky; often relieved with vomiting
- vomiting: large volumes, bilious, frequent
- tenderness: epigastric or periumbilical; quite mild unless strangulated
- distention: absent
- obstipation: may not be present
proximal small bowel obstruction (open loop)
- pain: intermittent to constant
- vomiting: low volume and frequency; progressively feculent with time
- tenderness: diffuse and progressive
- distention: moderate to marked
- obstipation: present
Distal small bowel obstruction (open loop)
- pain: progressive, intermittent constant; rapidly worsens
- vomiting: may be prominent (reflex)
- tenderness: diffuse, progressive
- distention: often absent
- obstipation: may not be present
small bowel obstruction (closed loop)
- pain: continuous
- vomiting: intermittent, not prominent; feculent when present
- tenderness: diffuse
- distention: marked
- obstipation: present
colon and rectum obstruction
type of bowel obstruction with no distention
proximal small bowel (open loop)
AXR: obstruction
air-fluid level, distended loops of small bowel, distal decompression
tx: 3rd spacing of fluid into bowel lumen with obstruction
need aggressive fluid resuscitaiton
why is there air with bowel obstruction?
from swallowed nitrogen
tx: bowel obstruction
bowel rest, NGT, IVF, -> cures 80% of partial SBO, 40% of complete SBO
obstruction: surgical indications
progressing pain, peritoneal signs, fever, increasing WBCs (all signs of strangulation or perforation), or failure to resolve
small bowel obstruction from gallstone usually in the terminal ileum
gallstone ileus
imaging: what do you see in gallstone ileus?
classically see air in the biliary tree in a patient with small bowel obstruction
what causes gallstone ileus?
caused by a fistula between the gallbladder and second portion of duodenum
tx: gallstone ileus
remove stone from terminal ileum
- can leave gallbladder and fistula if patient too sick
- if not too sick, perform cholecystectomy and close duodenum
2 ft from ileocecal valve
2% of population
usually presents in 1st 2 years of life with bleeding; is a true diverticulum
- accounts for 50% of all painless lower GI bleeds in children
meckel’s diverticulum
what causes meckel’s diverticulum?
caused by failure of closure of the omphalomesenteric duct
most common tissue found in meckel’s (can cause diverticulitis)
pancreas tissue
most likely to be symptomatic (bleeding most common) - tissue in meckel’s diverticulum
gastric mucosa
two types of tissue in meckel’s diverticulum
pancreatic and gastric tissue
adults: MC presentation of meckel’s diverticulum
obstruction
when do you remove meckel’s diverticulum?
incidental -> usually not removed unless gastric mucosa suspected (diverticulum feels thick) or has a very narrow neck
dx: meckel’s diverticulum
can get a meckel’s scan (99Tc) if having trouble localizing (mucosa lights up)
Tx: meckel’s diverticulum
diverticulotomy for uncomplicated diverticulitis or bleeding
- Need segmental resection for complicated diverticulitis (e.g. perforation), neck has > 1/3 the diameter of the normal bowel lumen, or if diverticulitis involves the base
what do you need to rule out in duodenal diverticula?
gallbladder-duodenal fistula