Which Structure in the Body Is Responsible for the Absorption of Nutrients From Food?

The food you eat needs to be digested and absorbed so your body can use the nutrients. Digestion, absorption and elimination of wastes takes place in the digestive system. Absorption of nutrients occurs in the small intestine, which is divided into three parts: the duodenum, jejunum and ileum.

Duodenum

The duodenum is the first section of the small intestine. It starts at the stomach and ends at the jejunum, which is the second part of the small intestine. Foods that have been mixed with stomach acid move into the duodenum. The gallbladder secretes bile into the duodenum and the pancreas secretes enzymes that break carbohydrates, fats and proteins into small components.

Jejunum

The jejunum is the middle section of the small intestine. It joints the duodenum and ends at the ileum. The jejunum is approximately 3 to 6 feet long. Absorption of nutrients begins in the jejunum, which is wrapped by involuntary muscles that move food through the small intestine by peristalsis. Absorption of the nutrients, or transport, across the jejunum wall can be active or passive. Active transport takes more energy to complete.

Ileum

The ileum is similar to the jejunum. It's the last portion of the small intestine, and is about 6 to 9 feet long. Food continues through by peristalsis and the final stages of absorption are completed in the ileum. Any remaining food moves into the large intestine where water is absorbed and waste continues to the rectum.

Malabsorption Problems

Some health conditions reduce the ability of the small intestine to absorb nutrients and can result in nutritional deficiencies. Crohn's disease is an inflammation of the walls of the small intestine, and is due to a problem with the immune system. Lactose intolerance is due to the lack of an enzyme that digests milk sugars. The undigested sugars cannot be absorbed properly. Celiac disease is another disorder of the immune system where the small intestine is damage by gluten, the protein in wheat. The damage reduces the ability of the small intestine to absorb some nutrients.

References

• MedlinePlus.com: Duodenum
• Biology Online: Digestion and Absorption of Food
• National Digestive Diseases Information Clearinghouse; Celiac Disease; September 2008
• PubMed Health: Crohn's Disease
• PubMed Health: Lactose Intolerance
• Gastrointestinal Society of Australia: Small Intestine