Understanding Colonic Function

Colonic Function

Colonic Function Absorption

• The water content of faecal matter is reduced to 1000 1500 ml per day. Thus stools become solid. Similarly, sodium, potassium and bile salts are also absorbed.
• The significance of this is in cases of diarrhoea, there is loss of water, sodium, potassium and other electrolytes (choleretic diarrhoea).
• Amino acids and fatty acids are also absorbed slowly in the colon. After ileal resection, bile salts enter the colon and irritate the colon resulting in diarrhoea.

Colonic Function Secretion

• Colon also secretes K+ and Cl–. It is increased in colitis.
• Chloride secretion is increased in cystic fibrosis.

 Motility

• Colon has four types of motility: Propulsive, retropulsive, mass peristalsis and gastrocolic reflux. Thus, contents travel aborally. Retropulsive activity is more in the right colon, these allowing the contents to ‘churn’ more and more. Mass contractions are found more in the left colon—especially after meals.

Factors which stimulate the colonic motility: 

• Dietary fat, rich fibre diet, less water intake
• Physical activity—walking, change in posture, exercises
• Emotional activity

Colonic Function Motility Constipation:

• It depends upon several factors such as food habits, genetics, and social customs.
• Generally, a patient is said to have constipation if he passes less than 2 stools per week.
• In addition to the low-fibre diet, emotional feelings and many rectal diseases also cause constipation. Example—prolapsed rectum, solitary rectal ulcer syndrome. Colonic diseases such as megacolon—
• Hirschsprung disease is an important cause of constipation in children.
• Increasing constipation in elderly patient suggest carcinoma in the left colon. Needs to be evaluated by colonoscopy.

Colonic Function Recycling

• Recycling of various nutrients takes place in the colon.
• Examples: Fermentation of carbohydrates, short chain fatty acids and urea cycling.
• Butyrate is the main product of bacterial fermentation. It is required mainly as a fuel for colonic epithelium.
• To accomplish this, the colon depends highly on its bacterial flora, especially for degeneration and fermentation ability.
• So broad-spectrum antibiotics inhibit production of butyrates and produce diarrhoea.

Colonic Function Constipation:

• Digestion and absorption
• In a child—Hirschsprung’s disease
• Adult women—idiopathic/following childbirth
• Middle-aged women—following hysterectomy
• Elderly man—carcinoma left colon
• Constipation with severe pain—anal fissure
• Depression patient—psychotropic drugs—used to treat schizophrenia, antidepressants and antiepileptic drugs

Colonic Bacteria

• Anaerobic bacteria: They constitute more than 99%. The most common pathogen is Bacteroides fragilis (1010/g of faeces). Other organisms are clostridia, cocci, etc.
• Aerobic bacteria: Escherichia coli is the most common organism about 107/g of faeces. Other organisms are Klebsiella, Proteus and Enterobacter.
• Normal function: Bacteria degrade bile pigments, thus resulting in brown-coloured stools. They also help in colonic motility and absorption. Fatty acids produced by bacteria supply nutrition to the colonic epithelium. Bacteria also supply vitamin K to the host.

Prebiotics and Probiotics

Prebiotics and Probiotics Clinical application:

• When a person takes antibiotics, both the harmful bacteria and the beneficial bacteria are killed. Bacterial change in flora alters carbohydrate metabolism with decreased short-chain fatty acid absorption and results in osmotic diarrhoea.
• In a similar fashion, antibiotic therapy causes an increase in the growth of Clostridium difficile. Thus, probiotics have been recommended for antibiotic-induced diarrhoea.
• Also, they have been used to treat diarrhoea in ulcerative colitis, in pouchitis (inflammation of the pouch after total proctocolectomy for ulcerative colitis) and in necrotising colitis in children.