1. By Christine Richardson and Catherine Boynton

2.  Hormones are chemical messengers  Secreted into the blood by endocrine organs  Chemical substances produced by specialized ductless glands that are released in the blood and carried to other parts of the body to produce specific regulatory effects. (http://tw3a.siuc.edu/426intro.htm)http://tw3a.siuc.edu/426intro.htm  Hormones are chemical signals that are secreted by cells that diffuse locally in the extracellular fluid that is picked up in the blood, and then distributed throughout the body.

3.  Homeostasis is the body’s ability to remain at equilibrium.  How the body organs function together to maintain a stable internal environment for the general well-being of the body (http://tw3a.siuc.edu/426intro.htm)

4.  Primary mechanism in charge of maintaining homeostasis  The change is put in the opposite direction of how it originally began

5.  Not used to maintain homeostasis  Sometimes it works with the negative feedback loop  The change that takes place is in the same direction that it originally began in  Important in certain responses such as “Fight-or-Flight”Response

6.  Insulin decreases blood glucose  Insulin causes glucose release from liver  Glucagon increases blood glucose  Glucagon causes glucose to be released from the liver

8.  Homeostasis maintains the internal environment between limits.  Negative feedback is used to do so. Any change from a set point results in an opposite change.

9.  The hypothalamus is responsible for monitoring the temperature of the blood which is normally close to 37 degrees. If there are significant fluctuations from this set point, the hypothalamus sends signals (messages carried by neurons) to different parts of the body to restore the temperature back to the set point. This is done through negative feedback.

10.  If blood temperature significantly increases above the set point Skin arterioles increase in diameter so that more blood flows to the skin. By doing so it transfers heat from the core of the body to the skin and this heat is then lost to the external environment, cooling down the body in the process. Skeletal muscle stays relaxed so that more heat is not generated. Sweat glands secrete large amounts of sweat which makes the surface of the skin moist. When water evaporates from the moist skin it cools down the body. If blood temperature significantly drops bellow the set point Skin arterioles decrease in diameter so that less blood flows to the skin. The diameter of the capillaries in the skin cannot change but less blood flows through them. This prevents heat loss to the external environment as the temperature of the skin falls. Shivering occurs. This is when the skeletal muscle does many small rapid contractions to generate heat. Sweat glands to not secrete sweat and so no water evaporation can occur as skin stays dry.

11.  Blood glucose concentration does not have a specific set point like blood temperature. Blood glucose levels drop and rise through the day and so the body usually tries to keep blood glucose levels around 4 to 8 millimoles per dm 3 of blood. Once again, negative feedback is used to do so. There are responses by target organs which affect the rate at which glucose is taken up from the blood or loaded into the blood.

12. Response to blood glucose levels above the set point β cells in the pancreatic islets produce insulin. Insulin stimulates muscle cells and the liver cells to take up glucose from the blood and convert it into glycogen. These are then stored in the form of granules in the cytoplasm of cells. Also, other types of cells are stimulated to take up glucose and use it for cell respiration instead of fat. All of these processes lower the levels of glucose in the blood. Response to blood glucose levels below the set point α cells in the pancreatic islets produce glucagon. Glucagon stimulates the liver cells to convert glycogen back into glucose and release this glucose into the blood. This raises the glucose levels in the blood.

13. Type I diabetes The onset is usually early, sometime during childhood. β cells do not produce enough insulin. Diet by itself cannot be used to control the condition. Insulin injections are needed to control glucose levels. Type II diabetes The onset is usually late, sometime after childhood. Target cells become insensitive to insulin. Insulin injections are not usually needed. Low carbohydrate diet can control the condition.