Human Biology 4.2

1. Human Biology 4.2 The endocrine system helps regulate body conditions.

2. Endocrine System • Controls the conditions in your body by making and sending chemicals from one part of the body to another. • controlled by the nervous system • Hormones are chemicals that are made in one organ and travel through the blood to a second organ • Often called chemical messengers • The target organ responds to the chemical • Many hormones affect all the cells in the body • Binds to receptors on the surface of or inside the target organ’s cells • Begins chemical changes that cause the target organ to function in a specific way.

3. Endocrine System • Work automatically • Different types perform different jobs • Examples • The hormone that causes red blood cells to be produced. • The parathyroid hormone that regulates calcium and phosphate levels • Some are made only during specific times in a person’s life • The hormone that controls the development of the sex organs • The hormones that regulate growth and sexual development

4. Hormones are the body’s chemicalmessengers.

5. Glands produce and release hormones.

7. Organ : Brain: controls muscle movement, thought processes. Gland : hunger, thirst, temperature, sleep, emotions Organ : Heart : pumps blood Gland : produces hormones that regulate blood pressure. Organ: Kidneys : filter waste Gland : regulate the production of red blood cells.

8. Control of the endocrine system includes feedback mechanisms. • Body is always trying to maintain homeostasis • Negative mechanisms turn off the response. • Increases in the amount of a hormone in the body feeds back to stop the production of that hormone. • Example: thyroxine • controls the body’s metabolism (rate at which the cells perform cellular respiration) by increasing cellular respiration. • The thyroid gland is controlled by the pituitary gland, whichiscontrolled by the hypothalamus. • Increased levels of thyroxine block the signals from the hypothalamus and the pituitary gland to the thyroid gland. • Production of thyroxine in the thyroid gland decreases.

9. Control of the endocrine system includes feedback mechanisms. • Positive feedback response is not to maintain homeostasis, but to produce a response that continues to increase. • Extreme responses that are necessary under extreme conditions. • Example: cut • Chemicals are released from damaged tissue that signal clotting. • Clotting causes more chemicals to form that increase clotting action. • The upward spiral increases until a clot is formed that fills the injured area. • Other examples of positive feedback include fever, the immune response, puberty, and labor.

10. Balanced hormone action • the action of one hormone is often balanced by the action of another. • When you ride a bicycle, you are able to ride in a straight line • Example: the pancreas produces two hormones. • Insulin decreases the level of sugar in the blood. • Glucagon, increases sugar levels in the blood. • Balance of hormones maintains stable blood sugar • Hormone Imbalance • too little or too much of any hormone can cause serious disease • Example: Diabetes mellitus • When the pancreas produces too little insulin, sugar levels in the blood can rise to dangerous levels. • High blood sugar levels can damage the circulatory system and kidneys. • Often treated by injecting synthetic insulin