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What Is the Function of the Small Intestine?

By Christine Lehman ; Updated July 27, 2017

The digestive system is made up of a number of parts, each of which plays a role in digestion. Food first enters your mouth, then goes down your esophagus into your stomach. After leaving your stomach, the food enters your small intestine, then your large intestine before it leaves the body. Despite its name, the small intestine is the most lengthy part of your digestive system and it plays an important role in the digestion and absorption of the food you eat.

Function of the Small Intestine

The small intestine is responsible for absorbing most of the nutrients found within your food. By the time ingested food reaches the small intestine, it has been mechanically broken down into a liquid. As this liquid flows across the inner surface of the small intestine (which has many small folds to increase the surface area), nutrients within the food come into contact with the many small blood vessels that surround the small intestine. This blood then leaves the small intestine, carrying away nutrients, water electrolytes, vitamins, minerals, fats and medications to the entire body. It can take three to six hours for a meal to pass from one end of the small intestine to the other, and that is dependent on the makeup of the food passing through; meals containing a lot of fiber move more quickly.

Parts of the Small Intestine

The small intestine has three parts: the duodenum, the jejunum and the ileum. The duodenum is the first portion of the small intestine, and it receives the contents of the stomach. When the contents of the stomach are pushed into the small intestine, they are very acidic, so this part of the small intestine is tolerant to low pHs. Soon after entering the small intestine, the pancreatic duct pours pancreatic enzymes into the digesting food. These enzymes reduce the acidity of the digesting food before it reaches parts of the small intestine that are not as tolerant to low pH. The bile duct, which carries bile from the liver, also empties into the duodenum and is responsible for breaking down fats within the food. The duodenum is the shortest part of the small intestine, measuring less than 10 inches long, and continues the digestive process that the stomach has started. The jejunum is where the majority of the absorption of nutrients takes place. The ileum is the longest part of the small intestine and is responsible for the absorption of B12 and the final processing of carbohydrates and proteins. The end of the ileum is where the small and large intestine meet and it's also where the appendix is located.

Locating the Small Intestine in the Body

The small intestine is located between the stomach and the large intestine, and is coiled up inside the abdominal cavity. The small intestine can be found in the abdomen, covered in a thin, fatty layer called the omentum. Inside, the small intestine has a number of folds--most of which are fed by blood vessels contained in a membrane that connects the small intestine together. This is called the mesentery.

Size of Small Intestine

The small intestine can reach lengths of up to 23 feet. It is much longer than the large intestine. The word "small" in small intestine, therefore, refers to its diameter rather than its length. The small intestine is much smaller around than the large intestine.

Benefits of a Healthy Small Intestine

The benefits of having the small intestine as the part of the digestive system responsible for absorption are many. The small intestine is very vascular, meaning it has a lot of blood flow to it. Therefore, nutrients, vitamins and medications can quickly and efficiently enter the body soon after leaving the stomach.

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