Sympathetic innervation promotes net absorption from the intestines.Parasympathetic innervation promotes net secretion from the intestines.The intestines are innervated by the enteric nervous system whose: Glucocorticoids and somatostatin - act to increase water and electrolyte absorption by increasing the action of the basolateral sodium-potassium ATP-ase.It also increases transcription of epithelial sodium channels. This increases the electrochemical gradient and driving force for sodium absorption.

Aldosterone - increases the net absorption of water and electrolytes by stimulating the basolateral sodium-potassium ATP-ase.

In the colon endocrine mechanisms used include: Regulation of AbsorptionĪbsorption in the gastrointestinal tract is regulated by neuroendocrine mechanisms. Vitamins and fats - short-chain fatty acids, crucial B vitamins (such as B6 and B12) and vitamin K (required for blood clotting) are produced by the digestion of chyme by the commensal microbial flora of the colon. Secretion usually occurs when the luminal concentration of potassium ions is below 25mM. In the colon potassium may be absorbed or secreted depending on the remaining concentration in the lumen and the electrochemical gradient created by the active absorption of sodium. This provides an electrochemical gradient for the movement of potassium into the plasma. Potassium - absorption of water along the length of the bowel concentrates potassium in the lumen. Water - the absorption of these electrolytes creates an osmotic gradient to allow further absorption of water. Chloride ions are exchanged for bicarbonate ions (causing net bicarbonate secretion). Sodium - this ion may be absorbed by various methods:Ĭhloride and bicarbonate - the movement of sodium into the plasma produces an electrochemical gradient to allow absorption of chloride. Fig 1 - Main functions of the large intestine In other words, it must move water against the gradient for osmosis. As the chyme is very concentrated by the time it reaches here, the colon must work against a larger osmotic pressure gradient than in the rest of the GIT. The colon helps to absorb a small volume of water from the lumen (400ml/day). The walls also contain gastrointestinal lymphoid tissue ( GALT) that contributes to the body’s immune defences. These protect the intestinal wall from the plethora of anaerobic bacteria in the colon and from the pressure exerted on the walls by the concentrated chyme (soon to become faeces). The large intestine is lined by mucosa with Crypts of Lieberkühn, which contain glands and the mucus-producing goblet cells.

In this article, we will review the functions of the large intestine and how they are achieved. Thus, the large intestine is specialised to work in the environment this produces. The chyme that enters the colon is already very concentrated because most of the water has already been absorbed.

The large intestine, or colon, has several roles including water absorption and immunity. Vitamins and fats – short-chain fatty acids, crucial B vitamins (such as B6 and B12) and vitamin K (required for blood clotting) are produced by the digestion of chyme by the commensal microbial flora of the colon. Potassium – absorption of water along the length of the bowel concentrates potassium in the lumen. Water – the absorption of these electrolytes creates an osmotic gradient to allow further absorption of water. Enhanced by absorption of short-chain fatty acids in the colon via specialised symportersĬhloride and bicarbonate – the movement of sodium into the plasma produces an electrochemical gradient to allow absorption of chloride.Sodium-hydrogen antiporter on the luminal membrane.Sodium – this ion may be absorbed by various methods: In the large intestine, there is a net absorption of sodium ions and chloride ions are actively absorbed.

Does the large intestine absorb water