Anatomy And Physiology

The Size and Functions of the Small and Large Intestine



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In our bodies, the digestive tract, otherwise known as the intestine, lies between the stomach and the anus. It is divided into two sections, namely the small and large intestine. The small intestine is about 6 meters long whilst the large intestine is about 1.5 meters long. Even though the small intestine is longer than the large intestine, it has a smaller diameter and hence, is called the small intestine.

After food has been churned into chyme in the stomach, it is released into the first part of the small intestine, called the duodenum. The pancreas releases digestive juices into the duodenum. Rich in enzymes, the juice helps to break down fats, proteins and carbohydrates in the chyme. In addition, the sodium bicarbonate present in the digestive fluid helps to neutralize the acid from the stomach. Bile produced by the gall bladder is also released into the duodenum and helps to break down fats. It is in the duodenum and jejunum, the middle section of the small intestine, where the chyme is broken down. In the third section of the small intestine called the ileum, nutrients are absorbed into the bloodstream. As a whole, most nutrients are digested and absorbed in the small intestine. Once every digestible ingredient has been absorbed from the chyme, the remainder is passed into the large intestine.

The large intestine comprises of 3 major sections: cecum, colon and rectum. It plays two very important roles. Firstly, it absorbs all remaining water from the food waste passed on from the small intestine. Secondly, it compacts the waste into a bundle so as to make excretion easier. The cecum is pouch-like and contains a valve which opens to receive chyme from the ileum. The colon absorbs water. In addition, the bacteria in the colon acts on and reduces the bulk of fiber in the feces. The rectum, the final segment of the digestive tract, is where feces are accumulated prior to discharge from the body through the anus.

In both the small and large intestine, the contents are pushed forward through peristalsis, a sequence of muscular contractions. Peristalsis consists of alternating waves of muscular contraction and relaxation, which together push forward the chyme and waste matter in the small and large intestine respectively. If the intestines are not functioning properly, various diseases and ailments such as constipation and Crohn's disease can occur. In addition, the intestine can sometimes protrude into the abdomen due to weakness in the abdominal wall and cause a hernia.

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