2. Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College. What is homeostasis? - Ability of an organism to maintain its internal environment, despite changes to its internal or external environment Process that occurs in all living things All organ systems work together to achieve homeostasis http://en.wikipedia.org/wiki/File:Tightrope_artist_Cologne_1.jpg

3. What things in your body need to be kept within a range? Body Temperature Blood pressure Blood pH O 2 and CO 2 concentration Osmoregulation-Water balance Blood glucose

4. kidneys : – regulate water & mineral salts concentration skin : – regulate body temperature liver & pancreas : – regulate blood glucose level Parts of Body involved kidney liver pancreas + skin tissue cells blood

5. The glucose concentration in the blood is controlled by the pancreas The pancreas contains cells which produce digestive enzymes but it also contains cells (alpha and beta cells) which produce the hormones insulin and glucagon If the glucose concentration rises, the beta cells release insulin If the glucose concentration falls, the alpha cells release glucagon Insulin stimulates the liver and muscles to remove excess glucose from the blood and store it as glycogen Glucagon stimulates the liver to convert its stored glycogen into glucose which is then released into the bloodstream 12 In this way, the concentration of glucose in the blood is kept within narrow limits

6. Blood pressure forces tissue fluid out of a clump of narrow capillaries The fluid trickles down this tubule and the useful substances such as glucose are reabsorbed into the blood The fluid contains urea, salts, glucose and other soluble substances Microscopic slice of kidney tissue In this tubule more or less water is reabsorbed to maintain the blood concentration Excess water, some salts and urea collect here before passing to the bladder as urine Kidney function 11