Tag: role of large intestine in digestion

The digestive system starts with the mouth, followed by the food pipe or oesophagus that opens into the stomach. The stomach secretes acid and powerful enzymes that continue the process of breaking the food down into simpler substances. From there, food moves to the small intestine, which is made up of three segments, i.e., the duodenum, jejunum, and ileum.

• The sigmoid colon is the part of the large intestine that is closest to the rectum and anus
  
• It forms a loop that averages about 35-40 cm in length
• The loop is typically shaped like a Greek letter sigma or Latin letter S

There are many bacteria that live in the large intestine of human. They live in symbiotic association. These are Lactobacillus, Bifidobacterium, Methanogens, Bacteroids, Enterococcus, Escherichia coli. Lactobacillus help in digestion, maintaining the pH balance and replacing the healthy bacteria in the gastrointestinal tract. It acts as a probiotic. Bifidobacterium is also a probiotic. It helps in metabolism of undigested carbohydrates. It also prevents pathogen colonization. Methanogen helps in the fermentation of organic matter to obtain energy. They help in breakdown of complex indigestible carbohydrates. Bacteroids helps in amino acid biosynthesis. Enterococcus helps in digestion of undigested carbohydrates and fibres.

In herbivores, the caecum stores food material where bacteria are able to break down the cellulose. This function no longer occurs in the human caecum, so in humans it is simply a dead-end pouch forming a part of the large intestine.

The major function of the large intestine is to absorb water from the remaining indigestible food matter and transmit the useless waste material from the body.

Colonoscopy is the endoscopic examination of the large intestine and the distal part of the small bowel with a CCD camera or a fibre optic camera on a flexible tube passed through the anus. It can provide a visual diagnosis and grants the opportunity for biopsy or removal of suspected colorectal cancer lesions. 

The large intestine also secretes K+ and Cl-. Chloride secretion increases in cystic fibrosis. Recycling of various nutrients takes place in colon. Examples include fermentation of carbohydrates, short chain fatty acids and urea cycling. 

The wall of the large intestine is lined with simple columnar epithelium. Instead of having the evaginations of the small intestine (villi), the large intestine has invaginations (the intestinal glands). While both the small intestine and the large intestine have goblet cells, they are abundant in the large intestine.