The last part of the gastrointestinal tract (GI tract) is formed by the colon. The colon (large intestine) consists of several parts and is about 5 to 6 ft. long. The colon’s main function is to absorb water and electrolytes and the propulsion of the intestinal contents towards the anal canal. The colon ends in the rectum and the anus. The main function of the rectum and anus is defecation.
The anatomy of the large intestine
The first part of the colon (see Figure 1. The colon and its parts) the caecum with attached the appendix vermiformis (appendix). Then the caecum ends in the ascending colon. The colon is composed of a ascending part (ascending colon), a transversal part (transversal colon), a descending part (descending colon), the sigmoid, the rectum and the anal canal. The wall of the colon consists of a mucous membrane. This mucous membrane is consisted in deep depressions, also called crypts.
The last part of the small intestine, the terminal ileum, opens into the first part of the large intestine, the caecum (see Figure 1). It is a bag-shaped section of the colon which is approximately 2 to 3 inches long. On the side of the bottom of the caecum is the vermiform appendix. The vermiform appendix lies in various ways in the abdominal cavity. The vermiform appendix is a saccular appendix of the colon from about 2,5 to 4 inches long.
The functions of the colon (large intestine)
The two most important functions of the large intestine, is that the colon acts as a reservoir for the contents of the intestine and the colon absorbs water and electrolytes. The reservoir function of the colon is mainly carried out by two parts of the colon. The caecum and ascending part of the colon acts as the reservoir function of the intestinal content. The second part of the colon which acts as the reservoir is the rectum. Each day there will be approximately 500 to 1500 milliliters of digested food in the colon. In the colon, this mass thickened. The mass is concentrated so far that eventually of the 500 to 1500 ml only 100-200 milliliters remains.
The motility of the colon
Different movements take place in the colon. There are movements in the colon which mixes the mass in the colon. There are also peristaltic waves. These peristaltic waves cause the mass in the colon to be transports both forward and backward. The function of a peristaltic wave is that moves the mass backwards is that the mass from the colon can be stored in the caecum. Finally, there is also a mass movement of the large intestine. The mass movement occurs approximately 2 to 3 times per day. It ensures that the contents of the large intestine from the caecum to the sigmoid is transported.
Disorders (diseases) of the large intestine
There are several disorders of the large intestine. Below are some conditions that can occur in the large intestine:
- Constipation
- Crohn’s Disease
- Ulcerative colitis
- Diverticulitis
- Colon tumors
- Colon cancer
References
S. Silbernagel, A. Despopoulus, 2001, Atlas van de fysiologie, Sesam, Baarn
H. Fritsch, W. Kuhnel, 2007, Atlas van de anatomie, Inwendige organen, Sesam, Baarn
P. Kumar, M. Clark, 2002, Clinical Medicine, Saunders
K.L. Moore, A. F. Dalley, 1999, Clinically oriented Anatomy, Lippincott, Williams & Wilkins