Editing Small bowel and nutrition


See separate topic under 'small bowel' - which is more focused on the surgical aspect of things

== Physiology ==

* Majority of fluid and electrolytes are reabsorbed in the ileum
** Only site of absorption of B12 and bile salts
* >90% of water and salt in colon is reabsorbed

== Effects of bowel resection ==

* Up to 50% of small bowel can removed or bypassed.
** Resection of proximal jejunum - no significant alteration in fluid and electrolyte absorption, as ileum and colon can pick up the slack entirely
** Resection of ileum
*** Clinically generally leads to diarrhoea and deficiencies
**** B12 malabsorption - macrocytic anaemia and peripheral neuropathy
**** Bile salt malabsorption - steatorrhoea, oxalate renal stones, gallstones
***** Loss of fat-soluble vitamins ADEK - poor wound healing, impaired calcium homeostasis, coagulopathy
*** Accelerated intestinal transit which leads to '''gradual undernutrition'''
*** Depletion of bile salt pool cannot be replaced by synthesis in absence of ileum
*** Loss of bile salts into colon also affects colonic mucosa, causing an additional reduction in level of absorptive capacity
*** Loss of 100cm of ileum causes steatorrhoea, which may necessitate the administration of oral cholestyramine. Sometimes restriction of oral fat intake will be necessary. Regular B12 IV will be necessary.
*** May need parenteral nutrition if <50cm small bowel remains
*** Need a high carbohydrate/low oxalate diet
*** May adapt over time to rely on artificial nutrition less
** Resection of >2m of small bowel and colon +/- end jejunostomy
*** Short gut syndrome - very challenging
*** '''See separate topic on 'short gut syndrome' under 'small bowel''''
*** Adaptation does not occur
*** Net absorbers
**** >100cm of residual jejunum and they absorb more water and sodium from diet than passes through the stoma
**** Can usually be managed without supplemental IV fluids
*** Net secretors
**** <100cm of residual jejunum and lose more water and sodium from their stoma than they take by mouth
**** Require supplemental IV fluids
**** Daily jej output may be >4 litres
**** Sodium content of jej losses will be about 90mmol/L. If hypotonic solutions e.g. water are drunk, sodium will be lost across bowel lumen through diffusion
**** Treatment - restrict hypotonic fluids to 1L per day, take glucose and saline replacement solutions
*** Complications of short bowel syndrome:
**** Peptic ulceration (related to gastric hypersecretion)
**** Cholelithiasis
**** Hyperoxaluria (increased absorption of oxalate in colon predisposes to kidney stones)
**** Syndrome of slurred speech, ataxia, altered affect - due to fermentation of malabsorbed carbohydrates in colon - treat with low carbohydrate diet
* Metabolic consequences arise with <150cm of small bowel - 'short gut syndrome'

[[Category:Nutrition]]
[[Category:Small bowel]]