Animal Form & Function
Homeostasis
AP Biology
Bloomington High School
Definition
Controlling the internal environment
Maintenance of stable internal
environment
Negative Feedback
Response produced opposes stimulus
Homeostasis restored
Positive Feedback
Response produced reinforces stimulus
Homeostasis not restored - disruption
continues
Rare
Example – Childbirth
Mechanism
Disruption
detected by
receptors
Homeostasis Control Center
evaluates
information &
directs
response
Effector
produces
response that
restores
homeostasis
Controlling Body Temperature
Temperature
receptors in skin
& hypothalamus
detect increase
temperature
Homeostasis Control Center
Hypothalamus
Evaporative cooling
Sweat glands
Heat lost from skin
increase
secretion
Blood vessels in
skin dilate
Controlling Body Temperature
Temperature
receptors in skin
& hypothalamus
detect decrease
temperature
Homeostasis Control Center
Hypothalamus
Heat generated
Muscles contract -
Heat conserved
Shiver
Blood vessels in
skin constrict
Controlling Blood Glucose Levels
Blood glucose
levels rise
Homeostasis Beta cells in
Normal pancreas
Glucose Levels release insulin
Cells take in
glucose
Blood glucose
levels drop
Controlling Blood Glucose Levels
Blood glucose
levels fall
Homeostasis Alpha cells in
Normal pancreas
Glucose Levels release
glucagon
Breakdown of
glycogen in
liver & skeletal
muscles
Blood glucose
levels increase
Controlling Blood Calcium Levels
Blood calcium
levels rise
Homeostasis Thyroid
Normal releases
Calcium Levels calcitonin
Ca2+ deposited
in bone
Kidneys reduce
uptake of Ca2+
Blood Ca2+
levels drop
Controlling Blood Calcium Levels
Blood calcium
levels fall
Homeostasis Parathyroid
Normal releases
Calcium Levels parathyroid
hormone
(PTH)
Ca2+ released
from bone
Kidneys increase
uptake of Ca2+
Blood Ca2+ levels
rise