Question

We are already familiar with the roles of insulin and glucagon in response to changes in blood sugar. The importance of glucose homeostasis in energy metabolism, as well as to water and pH balance, is highlighted by the many mechanisms that interact to regulate changes in plasma glucose. For example, during the cephalic phase of digestion (seeing, smelling, thinking about food), insulin release is stimulated well before digestion and absorption have a chance to increase blood sugar!

Furthermore, research indicates the presence of osmoreceptors in the lumen of the small intestine and in the hepatic portal vein .

1. What is the possible adaptive advantage to locating osmoreceptors in these specific organs (i.e. what condition would stimulate these receptors)?
2. Stimulation of these osmoreceptors triggers an increase in ADH secretion that is detectable within 1 min!    Is this response likely through nervous communication or endocrine communication? Justify your answer.

Answer 1

Some reasearch indicate the presence of osmoreceptors in the small intestine and portal vein. The adaptive advantage of locating osmoreceptors in these oragans is that the primary site for absorption of food(here carbohydrates or sugar) is small intestine and these nutrients are transported via the portal vein. Therefore, maximum contraction of the glucose/sugar from the food is encountered at the site of absorption and transportation channel which are small intestine and portal vein respectively. These osmoreceptors can regulate the osmotic pressure of blood according to the food taken in the diet.

Moreover, stimulation of these receptors triggers increase in ADH secretion within 1 minute. Since endocrine signals take some time to show action, the probable mode of action of these osmoreceptors is by nervous communication.