The small intestine
The small intestine is about 4.75–6 m (15–20 ft) long. It has an average diameter of 2.5 cm (1 in). It is looped and coiled and fills up much of the abdominal cavity (the space in the abdomen that contains the intestines and other organs). The small intestine is made up of the duodenum, jejunum and ileum. It is covered by mesentery.
The duodenum connects the stomach to the small intestine. Most digestive
The jejunum is the middle part of the small intestine, between the duodenum and ileum. Most digestion and nutrient absorption takes place in the jejunum.
The ileum is the last and longest part of the small intestine. The ileum absorbs nutrients from digested food and empties the waste into the large intestine.
Layers of the small intestine wall @(Model.HeadingTag)>
The small intestine is made up of the same 4 layers that make up most of the GI tract.
The mucosa is a mucous membrane. It is the innermost lining of the small intestine. It is made up of a:
- layer of
epithelial cells(called the epithelium)
- layer of loose connective tissue (called the lamina propria)
- very thin layer of muscle (called the muscularis mucosa)
The inner surface of the mucosa has many finger-like projections called villi. The villi increase the surface area of the small intestine, which helps it absorb digested food.
The submucosa is a layer of connective tissue that surrounds the mucosa. It contains mucous glands, blood vessels, lymph vessels and nerves.
Muscularis propria @(Model.HeadingTag)>
The muscularis propria lies outside the submucosa. It is a band of smooth muscle that helps move food through the small intestine.
The main functions of the small intestine are to break down, or digest, food and to absorb nutrients, such as
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