The Small Intestine/Bowel
The mixture of food, liquid, and digestive juice (chyme) that passes out of the stomach, in a regulated controlled manner, enters into the small intestine/bowel. The average total length of the normal small bowel in adults is about 7 meters/22 feet. The small intestine has 3 segments:
- the duodenum,
- the jejunum, and
- the ileum.
Each part or section performs an important role in nutrient absorption.
Duodenum – The chyme first enters into the duodenum where it is exposed to secretions that aid digestion. The secretions include bile salts, enzymes, and bicarbonate. The bile salts from the liver help digest fats and fat-soluble vitamins (Vitamin A, D, E, and K). Pancreatic enzymes help digest carbohydrates and fats. Bicarbonate from the pancreas neutralizes the acid from the stomach.
Jejunum – The chyme is then further transited down into the second or middle part of the small intestine, the jejunum. Mainly in the first half of the jejunum, the majority (about 90%) of nutrient absorption occurs involving proteins, carbohydrates, vitamins, and minerals.
Ileum – The ileum is the last section of the small intestine and leads to the large intestine or colon. The ileum mainly absorbs water, bile salts, and vitamin B12.
The ileocecal valve is a one-way valve located between the ileum and the cecum, which is the first portion of the colon. This valve helps control the passage of contents into the colon and increases the contact time of nutrients and electrolytes (essential minerals) with the small intestine. It also prevents back-flow (reflux) from the colon up into the ileum, and helps minimize the movement of bacteria from the large intestine up into the small bowel.
Large Intestine or Colon