Colon normal physiology

*fluid and electrolyte exchanges
- water, sodium, potassium, chloride, bicarbonate, and amonia.
Colon is a major site for waters absorption (1000-2000 mL/d) and electrolyte exchanges. Sodium is absorbed via Na-K ATPase. Water is absorbed passively along an osmotic gradient. Potassium is secreted into the colonic lumen and absorbed by passive diffusion. Chloride is absorbed via a chloride-bicarbonate exchange.
*short-chain fatty acids
Acetate, butyrate and propionate are produced by bacterial fermentation of dietary carbohidrates. Its important source of energi for the colonic mucosa
*colonic microflora and intestinal gas
Approximately 30% of fecal dry weight is composed of bacteria. endogenous microflora are crucial for the breakdown of carbohidrates and proteins in the colon and participate in the metabolism of bilirubin, bile acids, estrogen, and cholesterol also production of vit K.
*motility
The large intestine doesnt demonstrate cyclic motor activity. Colon displays intermitten contraction. Cholinergic activation increases colonic motility.
*defecation
Is a complex, coordinated mechanism involving colonic mass movement, increased intra-abdominal and rectal pressure, and relaxation of the pelvic floor.