1. Biology Sylvia S. Mader Michael Windelspecht
Chapter 31
Animal Organization and Homeostasis
Lecture Outline
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2. Biology, 9th ed, Sylvia Mader
Chapter 33
31.4 Homeostasis
Animal Organization & Homeostasis
The organ systems of the human body contribute to homeostasis
The ability of an organism to maintain a relatively constant internal environment
Animals vary to the degree in which they can regulate internal variables.

3. Biology, 9th ed, Sylvia Mader
Chapter 33
Homeostasis
Animal Organization & Homeostasis
The organ systems of the human body contribute to homeostasis
The digestive system
Takes in and digests food
Provides nutrient molecules that replace used nutrients
The respiratory system
Adds oxygen to the blood
Removes carbon dioxide
The liver and the kidneys
Store excess glucose as glycogen
Later, glycogen is broken down to replace the glucose used
The hormone insulin regulates glycogen storage
The kidneys
Under hormonal control as they excrete wastes and salts

4. Biology, 9th ed, Sylvia Mader
Chapter 33
Homeostasis
Animal Organization & Homeostasis
Homeostatic Control
Partially controlled by hormones
Ultimately controlled by the nervous system
Negative feedback is the primary homeostatic mechanism that keeps a variable close to a set value
Sensor detects change in environment
Regulatory center initiates an action to bring the conditions back to normal

5. Regulation of Room Temperature Using Negative Feedback
Biology, 9th ed, Sylvia Mader
Regulation of Room Temperature Using Negative Feedback
Chapter 33
Animal Organization & Homeostasis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Control center
sends data to
thermostat
directs furnace
to turn off
68°F set point
Sensor
70°F
too hot
furnace off
negative feedback
and return to
normal temperature
stimulus
too hot
Homeostasis
too cold
negative feedback
and return to
normal temperature
stimulus
Sensor
furnace on
66°F
too cold
Control center
directs furnace
to turn on
sends data to
thermostat 5
68°F set point

6. Regulation of Body Temperature by Negative Feedback
Biology, 9th ed, Sylvia Mader
Chapter 33
Regulation of Body Temperature by Negative Feedback
Animal Organization & Homeostasis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Control center
sends data to
control center
98.6°F set point
directs response
to stimulus
Sensor
Effect
Blood vessels dilate;
sweat glands secrete.
negative feedback
and return to normal
temperature
stimulus
above normal
Normal body temperature
below normal
negative feedback
and return to normal
stimulus
Effect
Sensor
Blood vessels constrict;
sweat glands are inactive.
Control center
directs response
to stimulus
sends data to
control center
98.6°F set point

7. Biology, 9th ed, Sylvia Mader
Chapter 33
Homeostasis
Animal Organization & Homeostasis
Positive feedback is a mechanism that brings about an ever greater change in the same direction
Childbirth process
Positive Feedback
Does not result in equilibrium
Does not occur as often as negative feedback

8. Biology, 9th ed, Sylvia Mader
Chapter 33
Positive Feedback
Animal Organization & Homeostasis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2. Signals cause pituitary gland to
release the hormone oxytocin.
As the level of oxytocin increases,
so do uterine contractions
until birth occurs.
pituitary gland + +
uterus
1. Due to uterine contractions,
baby’s head presses on
cervix, and signals are
sent to brain.