Anatomy And Physiology

Anatomy Physiology

Erich Rosenberger M.D.'s image for:
"Anatomy Physiology"
Image by: 

The small intestine and is an extremely vital organ in your gastrointestinal system. Along with the stomach, it is the major organ involved in the process of digestion. A large variety of nutrients such as carbohydrates, protein, fats, and many vitamins and minerals are absorbed by your small intestine. If your small intestine where to stop functioning properly, you would rapidly become malnourished.


Measuring over 6 meters in length, the small intestine stretches from your stomach to the beginning of your large intestine. For anatomical and medical classification it is broken in to three distinct zones - the duodenum, the jejunum, and the ilium. Despite its great length, the surface area of the small intestine is not sufficient to absorb all of the nutrients your body needs. Therefore, the structure of the small intestine contains millions of microscopic folds which act to increase the surface area. These folds increase the available surface area to absorb food and water.

The inner surface of the small intestine contains numerous finger-like projections, known as villi. Each of these villi contain many more folds, known as microvilli. Each finger-like villi contains a set of small blood vessels and part of the lymphatic system. These vessels are used in the transportation of nutrients which are absorbed from the surface cells.

These cells lining the inner surface of the small intestine are specially adapted for the absorption of nutrients and chemicals, which you have eaten or drank. The surface of the epithelial cells contain various carrier molecules, which are used to it absorb specific chemicals and nutrients as they passed through the small intestine.


There are three primary methods by which nutrients are absorbed from the small intestine. The first of these mechanisms is known as simple diffusion. Simple diffusion requires no energy input, and takes place when there is a high concentration on one side of the small intestine cells relative to a lower concentration on the other side. Nutrients flow from areas of high concentration to areas of lower concentration.

The second method of nutrient absorption of the small intestine is known as active transport. Active transport requires energy input and allows the transport of nutrients from an area of low concentration to an area of relatively higher concentration. There are typically proteins involved which act as carriers for the nutrients which are being absorbed. These carrier proteins are then transported across the surface of the small intestine cells.

The last method of nutrient absorption in the small intestine is known as facilitated diffusion. In facilitated diffusion there are carrier proteins, however no energy input is required to move the nutrients.

Types of nutrients absorbed in the small intestine

Carbohydrates are absorbed by the small intestine. Before they are absorbed by the cells, carbohydrates are broken down into simpler units along the brush border of the cells lining the small intestine. These simpler carbohydrates, in the form of glucose and other monosaccharides, are then absorbed by various methods such as diffusion and active transport.

The small intestine is also responsible for absorbing proteins. These proteins are partially digested by enzymes secreted into the small intestine by the pancreas. The presence of protein inside the small intestine activates the release of numerous enzymes, which act to break down these dietary proteins. Once broken down, carrier mediated transport absorbs the small pieces of protein and amino acids.

The final nutrient which is absorbed in the small intestine is fat. Fat is emulsified in the stomach, and further broken down in the duodenum by various pancreatic enzymes. Bile is released from the gallbladder, and key to the absorption of dietary fats. Bile binds with dietary fats and forms small clusters known as micelles. These micelles are then able to be absorbed by the cells lining the border of the small intestine.

There are numerous other vitamins and minerals which are absorbed by the small intestine. All of the water soluble by the vitamins, such as the B vitamins, are absorbed in the small intestine. The small intestine is responsible for much of the absorption of water by your body, although the large intestine functions for this also. Most electrolytes and trace minerals such as calcium, magnesium, iron, sodium, potassium, and others are absorbed in various parts of the small intestine.

The small intestine is a very important organ in your digestive system. Without it, you would rapidly become malnourished. It doesn't have the glamor and fame of other more prominent organs, such as the heart or brain - but make no mistake, you need it functioning efficiently if you plan on being healthy.


More about this author: Erich Rosenberger M.D.