Bowel eliminationPrepared by : Christian Raveina

Physiology of bowel elimination•Bowel elimination or defecation : defecation, also called bowel movement,  the act of eliminating solid or semisolid waste materials/feces from the digestive tract.• In human beings, wastes are usually removed once or twice daily, but the frequency can vary from several times daily to three times weekly and remain within normal limits.

•Muscular contractions (peristaltic waves) in the walls of the colon move fecal material through the digestive tract to the rectum.• The rectum is a distensible muscular tube that acts as a temporary reservoir for the waste material.• As the rectal walls expand with filling, stretch receptors from the nervous system, located in the rectal walls, stimulate the desire to defecate.

• The urge passes within one to two minutes if not relieved , and the material in the rectum is then often returned to the colon where more water is absorbed• If defecation is continuously delayed, constipation and hardened feces result.• When the rectum is filled, pressure within it is increased.• This increased intrarectal pressure initially forces the walls of the anal canal apart and allows the fecal material to enter the canal

• as material is entering, muscles attached to the pelvic floor help further to pull the anal canal walls apart. • The rectum shortens as it expels material into the anal canal, and peristaltic waves propel the feces out of the rectum. • In the anus there are two muscular constrictors, the internal and external sphincters, that allow the feces to be passed or retained.

• As feces exit, the anus is drawn up over the passing mass by muscles of the pelvic diaphragm to prevent prolapse (pushing out of the body) of the anal canal.•While defecation is occurring, the excretion of urine is usually stimulated. • The chest muscles, diaphragm, abdominal-wall muscles, and pelvic diaphragm all exert pressure on the digestive tract.

• Respiration temporarily ceases as the filled lungs push the diaphragm down to exert pressure. • Blood pressure rises in the body, and the amount of blood pumped by the heart decreases.

Colon rectumPeristaltic movement

StimulationThrough SRIncreased intrarectal

pressure

Forces the wallOf anal canal Fecal material enters

To anal canal Muscle of the pelvic floor

Pulls the anal canal wall apart

Int. Ext. sphincter Feces passed Anus dawn up

To prevent rectal Prolapse

Physiology of bowel elimination

Composition of feces 1. Water• 65-85% of stools are water. All the water drank by an individual is completely absorbed in the small and large intestine. In case of diarrhea, the water content of stools is more than 85%.

2. Protein• Protein from food is digested completely in the small intestine and is converted into amino acids before being absorbed in blood.

3. Fat• 95% of all fat consumed is absorbed in the small intestine. Traces of fat can definitely be found in stools. •However, fats in excess of 6% in stool are abnormal. A condition where the fat content of stools is greater than 6% is known as Steatorrhea.

4. Carbohydrate• Simple and complex carbohydrates would mean the sugar and starches in diet. • They are completely absorbed in the small intestine and assimilated in blood as glucose, fructose or galactose. • Undigested carbohydrates in normal stools should be below 0.5%.

5. Fiber• Fiber is completely indigestible and gives volume and bulk to stools. The more fiber one eats the more of undigested food wastes can be discharged from the body. • Otherwise, undigested food remnants may be left behind and could cause problems. • With a low fiber diet, undigested food would account for 5-7% of the total stool volume. With a high fiber diet, 10-15% of the undigested wastes could be discharged from the body.

Besides the five major components :• also contain mineral salts which are insoluble. They too cannot be digested by the body. This indigestible component of feces is known as Ash. 0.2 to 1.2% of normal stools is ash.• The stools also contain mucous shed from the inner lining of digestive tract. The mucus helps to bind together undigested food, intestinal bacteria and metabolic debris like dead cells or bile secreted by the liver etc.

Characteristics of feces •Normal colour :• Adult: brown• Infant: yellow

• Abnormal colour:• Clay or white: Absence of bile pigment (bile obstruction) or diagnostic study using barium• Black or tarry: Drug (e.g., iron), bleeding from upper gastrointestinal tract (e.g., stomach, small intestine), diet high in red meat and dark green vegetables (e.g., spinach)• Red: Bleeding from lower gastrointestinal tract (e.g., rectum), some foods (e.g. beets)• Pale: Malabsorption of fats, diet high in milk and milk products and low in meat

•Normal consistency: Formed, soft, semisolid, moist•Abnormal consistency •Hard, dry, constipated stool•Dehydration, decreased intestinal motility resulting from lack of fiber in diet, lack of exercise, emotional upset, laxative abuse•Diarrhea :Increased intestinal motility (e.g., irritation of the colon by bacteria)

•Normal shape: Cylindrical , about 2.5 cm (1 inch) in diameter in adults•Abnormal shape: Narrow, pencil-shaped, or string like stool•Obstructive conditional of the rectum

•Normal amount :• Varies with diet• About 100 to 400 g per day

•Normal odour: Aromatic, affected by ingested food and person’s own bacterial flora

• Abnormal odour: Pungent (sharply strong )• Infection, blood

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