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Its main function is to absorb vitamin B 12, bile salts, and whatever products of digestion that were not absorbed by the jejunum. The ileum follows the duodenum and jejunum and is separated from the cecum by the ileocecal valve (ICV). In humans, the ileum is about 2–4 m long, and the pH is usually between 7 and 8 (neutral or slightly basic).
Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here. Ileum: The final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum. It absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrients.
Creating cecotropes is a way to get more nutrients out of their food without adding a lot of bulk to their GI tract (which is 10% - 20% of their body weight). [6] Since their colons do not absorb the nutrients in the cecotropes, they reingest them so they can be absorbed in the small intestine.
Vitamin B12 and bile salts are absorbed in the terminal ileum. Vitamin B12 will only be absorbed by the ileum after binding to a protein known as intrinsic factor. Water is absorbed by osmosis and lipids by passive diffusion throughout the small intestine. Sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport
This can cause vitamin deficiencies due to the improper absorption of nutrients in the small intestine. The small intestine can also be obstructed by a volvulus, a loop of intestine that becomes twisted enclosing its attached mesentery. This can cause mesenteric ischemia if severe enough. A common disorder of the bowel is diverticulitis.
Paracellular transport also has the benefit that absorption rate is matched to load because it has no transporters that can be saturated. In most mammals, intestinal absorption of nutrients is thought to be dominated by transcellular transport, e.g., glucose is primarily absorbed via the SGLT1 transporter and other glucose transporters .
In the small intestine, epithelium is simple columnar and specialised for absorption. It is organised into plicae circulares and villi, and the enterocytes have microvilli. The microvilli create a brush border that increases the area for absorption. In the ileum there are occasionally Peyer's patches in the lamina propria.
Finally, the conjugated bile acids which remained un-ionized conjugated bile acids are passively absorbed. Venous blood from the ileum goes straight into the portal vein and then into the liver sinusoids. There, hepatocytes extract bile acids very efficiently, and little escapes the healthy liver into systemic circulation.