In: Anatomy and Physiology
3 a. If you drank a bottle of water, how would this affect the osmolarity of the gastric fluids in the lumen of your small intestine and therefore the osmotic gradient across the epithelial cells lining the small intestine?
b. Based on your response to the previous question, how does the change in the osmotic gradient affect the osmolarity of the plasma? The volume of the plasma?
Water is secreted in the lumen of the small intestine during the process of digestion.Majority of the water is reabsorbed in the small intestine.Water flows through the mucosa in response to osmotic gadient. Sodium is absorbed through the intestinal lumen by several mechanisms, but most of it is done by cotransport of glucose and amino acids and Na+/H+ exchange. Sodium is absorbedand exported form the cells via sodium pumps. During the process, high osmolarity is generated in the intracellular spaces between the enterocytes.. The water then diffuses through osmotic gradient established by the sodium. The water and even sodium, later also diffuse in blood capillaries. In short, water is absorbed in the intestinal lumen by diffusion down the osmotic gradient.
Transport of water in blood on the other hand is done against the osmotic gradient. This enables the intestine to absorb water even when the osmolarity in the lumen is higher than that of the blood.