Final answer:
The absorption of Vitamin B12 is of most concern following a colectomy, especially if the terminal ileum is removed, leading to potential deficiency and serious health conditions.
Step-by-step explanation:
Following a colectomy, the absorption of Vitamin B12 would be of the most concern. Unlike other substances like glucose and water which are absorbed along the entire length of the intestine, Vitamin B12 is primarily absorbed in the terminal ileum, a part of the small intestine. If the colectomy involves removal of the terminal ileum, it can significantly impair the absorption of Vitamin B12. This vitamin is crucial for the production of red blood cells and neurological function, and its deficiency can lead to serious conditions such as megaloblastic anemia and neurological disorders. The body also stores Vitamin B12 in the liver, which can provide a reserve for a time, but eventually, a person may require supplementation if the absorption is compromised.