Small Intestine

          The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to describe the entire intestine. This article is primarily about the human gut, though the information about its processes is directly applicable to most placental mammals. The primary function of the small intestine is the absorption of nutrients and minerals found in food.(A major exception to this are cows; for information about digestion in cows and other similar mammals, see ruminants.)


         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. 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.


          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.

FUNCTION:

         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.