Colonic Fluid and Electrolytes Absorption and Secretion

Abstract

The normal colon is an extremely efficient absorptive organ, reabsorbing over 90% of the fluid and electrolytes it receives from the small intestine and from its own secretions. The rich colonic luminal microbiome modifies the luminal chyme and colonic function. Colonic fluid absorption and secretion are regulated by the coordinated action of systemic and local neural, endocrine and immune factors, and from the microbiome. A healthy colon exhibits net absorption of water, short chain fatty acids, sodium and chloride ions, a net secretion of potassium, bicarbonate and mucus, and an ability to transport ammonium ions. There is distinct crypt/surface and segmental heterogeneity of transport down the length of the colon, which are governed by an array of transporters and regulatory mechanisms. Although the colon can handle up to three times of its normal capacity of fluid, abnormalities in transporters or their regulation can lead to devastating excessive fluid retention resulting in constipation or life threatening excessive fluid and electrolyte loss resulting in diarrhea.