1. Animal Form & Function Homeostasis
AP & Pre-AP Biology
Serrano High School

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

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

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

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

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

10. Controlling Blood Calcium Levels
Blood calcium levels rise
Got Milk & a whole mess of Ca2+
Homeostasis Normal Calcium Levels
Thyroid releases calcitonin
Ca2+ deposited in bone Kidneys reduce uptake of Ca2+ Blood Ca2+ levels drop

11. Controlling Blood Calcium Levels
Blood calcium levels fall
Milk – I’m supposed to drink milk?
Homeostasis Normal Calcium Levels
Parathyroid releases parathyroid hormone (PTH)
Ca2+ released from bone Kidneys increase uptake of Ca2+ Blood Ca2+ levels rise