Colon and Defecation Prof K Sivapalan Functions of
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Colon and Defecation Prof. K. Sivapalan.
Functions of Colon • Convert about 1500 ml of chyme into 250 ml of semisolid feces. • Storage and periodic discharge of feces. • Protection from harmful bacteria that colonize the colon. 2013 Colon and Defecation 2
Movements and Secretion • • • Segmentation contractions for mixing. Peristalsis for propagation. Receptive dilation in sigmoid colon Mass action contractions with defecation reflex. Secretion: – Antibodies from lymphoid tissue – mucus from mucus glands. – electrolytes with water from Crypts of Liebercühn. • Irritation and anxiety increase secretion and motility and cause diarrhea. 2013 Colon and Defecation 3
Bacteria in Colon • Bacilli (E. Coli, anaerobic bacilli – tetanus, Gasgangreen), Cocci etc. • Digest mucus and produce vitamins. [absorption of which is questionable] • Immune deficiency, radiation, debilitation can result in dangerous infection and death. Putrefaction after death. • Toxic substances produced [including ammonia] detoxified in liver. • Organic acids produced acidify stool. • Odor of the feces- indole and skatole. 2013 Colon and Defecation 4
Absorption in colon. • Water and electrolytes [sodium]- against osmosis and solidifying feces. • Absorptive capacity is great because drugs administrated through rectum are absorbed well. • Water and electrolytes given in enema can be absorbed. Water enema can cause water intoxication in children. 2013 Colon and Defecation 5
Feces • One third is water. • One third is bacteria. • One third is dietary fiber. 2013 Colon and Defecation 6
Rectum and Anus • Rectum is usually empty. • When pressure increases, rectum contracts and internal anal sphincter relaxes. • External sphincter contracts until 55 mm Hg. It can be voluntarily relaxed or kept contracted. 2013 Colon and Defecation 7
Defecation • When feces fills sigmoid colon over flows and distend the rectum. • It is felt as urge to defecation, including the type of material in rectum. • Sacrel segments initiate defecation reflex. • Parasympathetic activity leads to mass action contraction. • External sphincter is contracted or relaxed voluntarily depending on the circumstances. • Increased abdominal pressure also can initiate defecation reflex. • If opening is delayed, parasympathetic activity dies down until another occasion. • Usually defecation occurs as a conditioned reflex. 2013 Colon and Defecation 8
Gastro-colic reflex. • Distension of the stomach initiates defecation reflex through nervous mechanism. • Babies defecate soon after feeding. • As voluntary control and conditioning is established, the reflex becomes inefective. • In Colitis, the reflex is facilitated. 2013 Colon and Defecation 9
Disorders • ILEOSTOMY- colonal diseases- water and electrolyte loss and inconvenience. • Megacolon- [Hirschsprung’s disease] – absence 2013 Colon and Defecation 10