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Colon and Defecation

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. Movements and Secretion. Segmentation contractions for mixing.

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Colon and Defecation

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  1. Colon and Defecation Prof. K. Sivapalan.

  2. 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. Colon and Defecation

  3. 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. Colon and Defecation

  4. 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. Colon and Defecation

  5. 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. Colon and Defecation

  6. Feces • One third is water. • One third is bacteria. • One third is dietary fiber. Colon and Defecation

  7. 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. Colon and Defecation

  8. 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. Colon and Defecation

  9. 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. Colon and Defecation

  10. Disorders • ILEOSTOMY- colonal diseases- water and electrolyte loss and inconvenience. • Megacolon- [Hirschsprung’s disease] – absence Colon and Defecation

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