Dietary fluid and intestinal secretions account for 7.5-10 litres water handled by the intestine per day. Of this, only 200 ml is excreted in the faeces daily, the majority being re-absorbed in the small intestine and about 400 ml in the colon.
Water absorption can be regulated to some extent by the autonomic nervous system by its effects of sodium and chloride absorption. Sympathetic stimulation or cholinergic inhibition leads to an increase in sodium and water absorption. In addition to its renal effects, the mineralocorticoid aldosterone also has effects on sodium and water absorption in the intestine, particularly the colon. Aldosterone increases the number of sodium channels on the epithelium and the number of Na/K pumps on the basolateral membrane, therefore, increasing sodium and water absorption.
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