Describe the role of hypothalamus in homeostasis.

a)Osmoregulation;
-When the osmotic pressure of the blood rises above normal (as a result of dehydration), the osmoreceptors in the hypothalamus are stimulated; which stimulates the pituitary gland to secrete a hormone called anti-diuretic hormone; (ADH) or vasopressin into the blood;
-On reaching the kidney, Anti-diuretic hormone (ADH) or vasopressin causes the kidney tubules to be more permeable to water; more water is reabsorbed into the blood stream lowering osmotic pressure of the blood; producing a concentrated urine.
-When the osmotic pressure of the blood falls below normal, hypothalamus is less stimulated; hence the pituitary gland is less stimulated, less Anti-diuretic hormone (ADH) or vasopressin is released into the blood stream;
-The kidney tubules become less permeable to water; and less re-absorption of water into blood stream takes place hence osmotic pressure of blood rises; and dilute urine is produced.
b)Thermoregulation;
-When the body temperature rises above normal, the hypothalamus is stimulated; which sends impulse to the skin; this causes the arterioles to dilate causing more blood flows near the skin surface; hence more heat is lost;
-When it is cold/ when the body temperature falls below normal, the hypothalamus detects it; and sends impulse to the skin; this causes the arterioles to constrict constrict/ vasoconstrict (vasoconstriction); less blood flows near the skin surface hence less heat is lost/ heat is conserved;
-When the temperature falls below the normal/ when it is cold, the hypothalamus sends impulse to the liver; the liver increases the rate of metabolic reactions producing heat energy; which is distributed throughout the body thus increasing the body temperature;
c)Blood sugar regulation;
-When there is excess sugar/rises above normal; the hypothalamus is stimulated which stimulates the pancreas to secrete insulin hormone;
-Insulin stimulates liver cells to convert the excess glucose to glycogen or fats for storage increase oxidation of glucose, inhibit conversion of glycogen to glucose; lowering blood sugar level to normal/ optimum level;
-When the blood sugar level drops below normal, the hypothalamus is stimulated which stimulate the pancreas to secrete glucagon hormone; glucagon stimulates the liver cells to convert glycogen and fats to glucose, reduce the breakdown of glucose; thus raising blood sugar level to normal/ optimum level;