2. It is a three-part organ
The small intestine is very efficient, it’s an invisible worker that plays its part in the seamless digestive process. The organ is a divided into 3 parts that include:
- The duodenum
- The jejunum
- The ileum
The duodenum is the shorter than the jejunum, while the ileum is the longest part of the small intestine.
There is actually division of labor among different segments. In other words, each of the small intestine parts must perform a specific assigned task. Here’s a summary of the functions of each segment.
Duodenum:
The first and shortest segment of the small bowel, duodenum connects the stomach to the jejunum. This C-shaped hollow tube measures around a foot in length. Duodenum receives food from the stomach in the form of chyme and mixes it with bile juice and the pancreatic secretions. It neutralizes the partially digested food with the help of alkaline mucus containing a high concentration of bicarbonate ions. The mucus is secreted by the Brunner’s glands present only in the duodenum.
The enzymatic secretions help in the digestion of carbohydrates, proteins and fats. So, the process of chemical digestion that started in mouth gets completed here. It also prepares food for absorption in microvilli.
Jejenum:
The jejunum is the second or middle part of the small intestine. In terms of length, it is longer than duodenum and shorter than ileum. Measuring around 8 feet.
While the duodenum carries out and completes the chemical digestion, the jejunum is the principal site for the absorption of nutrients from the digested food. This is the part where over 90% absorption of the foodstuffs takes place.
Food is absorbed into the bloodstream through finger-like projections called villi. Though villi are present across all segments of small bowel, they are longer and more active in the jejunum. The folds in the epithelium, villi and microvilli collectively contribute to incredibly increase the surface area for absorption.
The jejunum also has a pH between 7 and 9. This means it is slightly alkaline.
Ileum:
The third and longest segment of small bowel is the ileum, it is about 12 feet long.
The layers of longitudinal and smooth muscles in the ileal wall are thinner than those of other parts of small intestine.
Regarding its role in digestive system, the ileum contains receptors for absorption of vitamin B12 and bile salts. Meanwhile, it also absorbs the leftover nutrients from the digested food.
In 1667, Hans Conrad Peyer, a Swiss anatomist, discovered bundles or patches of lymphatic cells in ileum (the lymphatic system is part of the immune system that protects the body from infections). These patches are named after him as Peyer’s patches.
They can be seen with the naked eye as elongated thickened areas. We all have about 30 to 40 of such patches in our small intestines.
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