Functions of Ileum

Q: When surgery of intestine is considered, which important function(s) of ileum should be considered? 

A) Vitamin B12 absorption 
B) Bile acid absorption 
C) "Ileal brake" 
D) Fluid absorption 
E) All of the above


Answer: E

When the resection of the intestine become inevitable for various reasons, being an ICU physician it may be of importance to know some very important functions of ileum while parenteral or enteral nutrition is considered postoperatively.

Out of all of the above, probably the most important to know is that the distal 50 cm of the ileum is the primary site for vitamin B12 absorption, as resection of the terminal ileum is very common in short bowel syndrome (SBS). It requires lifelong vitamin B12 supplementation. 

Second most important to know that the distal ileum is the 'selective site' for bile acids absorption, and need close observation for malabsorption of fat as well as fat-soluble vitamins. Another secondary effect of non-absorption of bile acid is the colonic secretomotor diarrhea. 1

 "Ileal brake" is an interesting and a less known concept. Unabsorbed lipids reaching the ileum cause a delay in gastric emptying which can be beneficial if residual ileum can be spared during the surgery. 2,3

Ileum has an active salt transport which facilitates the reabsorption of the fluid secreted by the jejunum. Also, it helps in the absorption of fluid entering the gut via hypertonic feedings. 4

#nutrition
#surgicalcriticalcare



References:

1. Hofmann AF, Poley JR. Role of bile acid malabsorption in pathogenesis of diarrhea and steatorrhea in patients with ileal resection. I. Response to cholestyramine or replacement of dietary long chain triglyceride by medium chain triglyceride. Gastroenterology 1972; 62:918. 

2. Welch IM, Cunningham KM, Read NW. Regulation of gastric emptying by ileal nutrients in humans. Gastroenterology 1988; 94:401. 

3. Van Citters GW, Lin HC. Ileal brake: neuropeptidergic control of intestinal transit. Curr Gastroenterol Rep 2006; 8:367.

4. Fordtran JS, Rector FC Jr, Carter NW. The mechanisms of sodium absorption in the human small intestine. J Clin Invest 1968; 47:884.