1. Animal Form & Function Homeostasis AP Biology

2. Definition  Controlling the internal environment  Maintenance of stable internal environment

3. Negative Feedback  Response produced opposes stimulus  Homeostasis restored

4. Positive Feedback  Response produced reinforces stimulus  Homeostasis not restored - disruption continues  Rare  Example – Childbirth

5. Mechanism Homeostasis Disruption detected by receptors Control Center evaluates information & directs response Effector produces response that restores homeostasis Disruption

6. Controlling Body Temperature Homeostasis Temperature receptors in skin & hypothalamus detect increase temperature Control Center Hypothalamus Sweat glands increase secretion Blood vessels in skin dilate Hot Day in the sun Evaporative cooling Heat lost from skin

7. Controlling Body Temperature Homeostasis Temperature receptors in skin & hypothalamus detect decrease temperature Control Center Hypothalamus Muscles contract - Shiver Blood vessels in skin constrict Cold day in January Heat generated Heat conserved

8. Controlling Blood Glucose Levels Homeostasis Normal Glucose Levels Blood glucose levels rise Beta cells in pancreas release insulin Cells take in glucose Blood glucose levels drop Eating an ice cream sundae

9. Controlling Blood Glucose Levels Homeostasis Normal Glucose Levels Blood glucose levels fall Alpha cells in pancreas release glucagon Breakdown of glycogen in liver & skeletal muscles Blood glucose levels increase No breakfast today

10. Controlling Blood Calcium Levels Homeostasis Normal Calcium Levels Blood calcium levels rise Thyroid releases calcitonin Ca 2+ deposited in bone Kidneys reduce uptake of Ca 2+ Blood Ca 2+ levels drop Got Milk & a whole mess of Ca 2+

11. Controlling Blood Calcium Levels Homeostasis Normal Calcium Levels Blood calcium levels fall Parathyroid releases parathyroid hormone (PTH) Ca 2+ released from bone Kidneys increase uptake of Ca 2+ Blood Ca 2+ levels rise Milk – I’m supposed to drink milk?