Homeostasis and Hormonal Control (chapter 9)

Homeostasis definition

Homeostasis is the maintenance of a constant internal environment.

Hormone definition

A hormone is a chemical substance produced in minute quantities by an endocrine gland. It is transported in the bloodstream to target organs where it exerts its effect.

When blood glucose concentration rises above normal

1. Blood glucose concentration rises above normal (stimulus)

2. Islets of Langerhans in the pancreas are stimulated (receptor)

3. Corrective mechanism

   1. The islets of Langerhans secrete more insulin into the bloodstream.

   2. Blood transports the insulin to the liver and muscles

   3. Insulin increases the permeability of the cell membrane to the glucose. Glucose is absorbed more quickly by the cells.

   4. Insulin increases the rate of respiration.

   5. Insulin causes the liver and muscles to convert excess glucose to glycogen. Glycogen is stored in the liver and muscles.

4. Blood glucose concentration decreases. This provides a feedback to the receptor to reduce insulin production.

When blood glucose concentration falls below normal

1. Blood glucose concentration falls below normal. (stimulus)

2. Islets of langerhans in the pancreas are stimulated (receptor)

3. Corrective mechanism

   1. The islets of langerhans secrete more glucagon into the bloodstream.

   2. The blood transports the glucagon to the liver and muscles.

   3. Glucagon causes the conversion of stored glycogen back to glucose.

   4. From the liver, glucose enters the bloodstream.

4. Blood glucose concentration increases. This provides a feedback to the receptor to reduce glucagon production.

when body temperature rises above normal

1. Body Temperature rises above normal.

2. Thermoreceptors in the skin and hypothalamus are stimulated.

3. he arteriole in the skin dilate. This allows more blood to flow through the capillaries in the skin. Hence, more heat will be lost through the skin.

4. Sweat glands become more active and produce more swear. As more water in the sweat evaporates from the surface of the skin, more heat is lost from the body. This is an efficient means of losing heat.

5. The metabolic rate is decreased. This reduces the amount of heat releases within the body.

6. Body temperature decreases.

Body temperature begins to fall

1. Body temperature falls below normal.

2. Thermoreceptors in the skin are stimulated. Impulses are transmitted to the hypothalamus in the brain.

3. The arterioles in the skin constrict. This allows less blood to flow through blood capillaries. Hence, less heat will be lost through the skin.

4. Sweat glands become less active and produce less sweat. As less water in the swear evaporates from the surface of the skin, less heat is loss from the body.

5. the metabolic rate is increased. this increases the amount of heat released within the body.

6. When the above responses are not sufficient to prevent a drop in body temperature, shivering occurs. This rapid contraction and relaxation of the skeletal muscles increases the amount of heat released.

7. Body temperature returns to normal