GIT Regulation and Diarrhea

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[REGULATION OF THE GASTROINTESTINAL TRACT] *** *** *** *** *** *** [DIARRHEA] - Guyton WATER LOSS IN FECES: Only a small amount of water (100 ml/day) normally is lost in the feces. This can increase to several liters a day in people with severe diarrhea. ** For this reason, severe diarrhea can be life threatening if not corre cted within a few days. Loss of fluid from all fluid compartments of the body is called DEHYDRATION. ** This, too, can reduce the blood volume and cause hypovolem
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  [REGULATION OF THE GASTROINTESTINAL TRACT]*** *** *** *** *** ***[DIARRHEA] - GuytonWATER LOSS IN FECES:>> Only a small amount of water (100 ml/day) normally is lost in the feces.>> This can increase to several liters a day in people with severe diarrhea.** For this reason, severe diarrhea can be life threatening if not corrected within a few days.>> Loss of fluid from all fluid compartments of the body is called DEHYDRATION.** This, too, can reduce the blood volume and cause hypovolemic shock similar to that resulting from hemorrhage.HYPONATREMIA:>> Decreased plasma sodium concentration can result from loss of NaCl from the extracellular fluid or addition of excess water to the extracellular fluid.>> A primary loss of sodium chloride usually results in hypo-osmotic dehydrationand is associated with decreased extracellular fluid volume.** Conditions that can cause hyponatremia owing to loss of NaCl includeDIARRHEA and VOMITING.METABOLIC ACIDOSIS:>> Severe DIARRHEA is probably the most frequent cause of metabolic acidosis.** The cause of this acidosis is the loss of large amounts of NaHCO3 into the feces.** The gastrointestinal secretions normally contain large amounts of bicarbonate.** Diarrhea results in the loss of HCO3  from the body, which has the sameeffect as losing large amounts of HCO3- in the urine.** This form of metabolic acidosis is particularly serious and can causedeath, especially in young children.PERISTALSIC RUSH:>> Although peristalsis in the small intestine is normally weak, intense irritation of theintestinal mucosa, as occurs in some severe cases of infectious diarrhea, can cause both powerful and rapid peristalsis, called the peristaltic rush.>> This is initiated partly by nervous reflexes.** Involves the ANS and brain stem and partly by intrinsic enhancement of the myenteric plexus reflexes within the gut wall itself.>> The powerful peristaltic contractions travel long distances in the small intestine within minutes.** Sweeping the contents of the intestine into the colon and thereby relieving the small intestine of irritative chyme and excessive distention.>> Excess MOTILITY causes less absorption and DIARRHEA or loose fecesDIARRHEA CAUSED BY EXCESS SECRETION OF H2O AND ELECTROLYTES IN RESPONSE TO IRRITATION::  >> Whenever a segment of the large intestine becomes intensely irritated, as occurs when bacterial infection becomes rampant during enteritis, the mucosa secretes extra large quantities of water and electrolytes in addition to the normal viscid alkaline mucus.** This acts to dilute the irritating factors and to cause rapid movement of the feces toward the anus.** The result is DIARRHEA, with loss of large quantities of H2O and electrolytes.** But the diarrhea also washes away irritant factors, which promotes earlier recovery from the disease than might otherwise occur.EXTREME SECRETION OF CHLORIDE IONS, SODIUM IONS, AND H20 FROM THE L.I. EPITHELIUM IN SOME TYPES OF DIARRHEA:>> Deep in the spaces between the intestinal epithelial folds are immature epithelial cells that continually divide to form new epithelial cells.**These in turn spread outward over the luminal surfaces of the intestines.>> While still in the deep folds, the epithelial cells secrete NaCl and H2O intothe intestinal lumen. This secretion in turn is reabsorbed by the older epithelial cells outside the folds, thus providing flow of water for absorbing intestinal digestates.>> The toxins of cholera and of some other types of diarrheal bacteria can stimulate the fold secretion.** This secretion often becomes much greater than can be reabsorbed** Thus sometimes causing loss of 5 to 10 liters of water and sodium chloride as diarrhea each day** Within 1 to 5 days, many severely affected patients die from this loss of fluid alone
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