Body temperature and blood glucose

1. Body temperature and blood glucose

2. Control of body temperature • The hypothalamus of the brain monitors temperature of the blood and compares it with a set point, usually close to 37ºC. Blood near the skin exchanges heat with the environment to preserve the temperature. • If the temp. is lower or higher, the hypothalamus sends messages to parts of the body to make them respond and bring the temperature back to the set point. (negative feedback). The messages are carried by neurons. • Vasoconstriction (constriction of the blood vessels) can decrease blood flow to the skin, preserving heat in cold weather.

3. Responses to overheating • Skin arterioles (blood vessels) become wider, so more blood flow through he skin. The temperature of the skin rises, so more heat is lost to the environment by radiation. • Rapid blood flow in capillaries keeps the skin warm • Skeletal muscles are relaxed, so that they don’t generate more heat. • Sweat glands secrete sweat, making the skin surface damp. Water evaporates from the damp skin and this has a cooling affect.

4. Responses to chilling • Skin arterioles become narrower ant bring less blood to the skin. Blood capillaries in the skin do not move, but less blood flows through them. Skin temperature falls, so less heat is lost to the environment. • Skeletal muscles shiver (small rapid contractions), to generate heat. • Skin remains dry, sweat glands do not secrete sweat. • http://www.think-bank.com/iwb/flash/homeostasis.html

5. Control of blood glucose • Blood glucose concentration can not be kept as steady as body temperature. Blood glucose levels are monitored by cells in the pancreas, which is both an endocrine and digestive organ. • The cells in the pancreas send hormone messages to the target organs when the glucose level is low or high. Example of negative feedback. Responses by target organs affect the rate at which glucose is loaded or unloaded into the blood. • Glucose concentration is kept between 4 and 8 millimoles per dm3.

6. Responses to high blood glucose levels • Beta cells in the pancreatic islets produce the hormone insulin. • Insulin lowers blood sugar levels. It stimulates the liver and muscle cells to absorb glucose. The glucose converts into glycogen. • Glycogen is stored in the cytoplasm of muscle cells. • Other cells are stimulated to absorb glucose and use it in cell respiration instead of fat.

7. Response to low blood glucose levels • Alpha cells in the pancreatic islets produce glucagon. • Glucagon is secreted when blood sugar is extremely low. • It stimulates liver cells to break glycogen down into glucose and release it into the blood (breakdown of stored fat). This results in a rise in blood glucose in the blood stream.

10. Diabetes mellitus • Diabetes occurs when control of blood glucose does not work effectively. Glucose concentration can fall beyond the normal limits. • Insulin deficiency or excessive tolerance – cells do not take up glucose, results in too much glucose (hyperglycemia) • Problems: - dehydration: lose excessive water from urination, blood pressure problems - starvation: body cannot use glucose

11. Type I Diabetes (Insulin dependent) Onset is usually during childhood Beta cells do not produce a sufficient amount of insulin (degeneration) Insulin injections are used to control blood sugar levels Type II Diabetes (Non-insulin dependent) Onset is usually after childhood, usually caused by obesity Target cells become insensitive to insulin Controlled by regulating dietary glucose (low-carbohydrate diet)