Learning Target: Mechanisms of Homeostasis
I Can… Explain how negative feedback mechanisms help
regulate and maintain a narrow range of internal conditions
in the human body among a wide range of external
conditions.
I Will…
• List and define the components of a control system
• Define feedback
• Explain how negative feedback works.
• Give an example of negative feedback in
the human body
• Give an example of positive feedback in
the human body
Learning Target: Mechanisms of Homeostasis
KEY CONCEPT: Humans need to regulate and
maintain a narrow range of internal environment
conditions among a wide range of external
environmental conditions in order to stay alive.
Primarily achieved by negative feedback
Learning Target: Mechanisms of Homeostasis
Why are there such narrow ranges
that need to be maintained?
Remember:
• Metabolism – all the chemical reaction in the body
• Enzymes can be easily denatured (altered & damaged)
• pH
• Temperature
• Concentrations
• Movement across membrane
• Substances that maintain
normal cell functioning
Learning Target: Mechanisms of Homeostasis
Control System:
• Sensors – receptors
• Gather information
• Internal Environment e.g. CO2 level in blood
• External Environment e.g. _______________
• Control Centers – Brain and Spinal Cord
• Evaluates / Interprets information from sensors
• Determines actions to be taken
Learning Target: Mechanisms of Homeostasis
Control System:
• Communication Centers – Carry messages from
control centers to targets
• Nervous system
• Endocrine system
•
Target – Organ, tissue, or cell that will carryout action
from communication center
• Alters functioning in response to message
• Maintains homeostasis
Learning Target: Mechanisms of Homeostasis
Feedback process:
• Information sent from sensors to control center
• Control center compares current conditions to ideal set
point conditions
• Control center determines action based on comparison
• Sends action instructions through communication
systems to target
• Target carries out action
• Information sent from sensors to control center
• Control center compares….
Constant loop
Learning Target: Mechanisms of Homeostasis
Negative Feedback – counteracts (works against) current
conditions to move back to ideal value
• Reverses current condition back to normal
• Primary method of maintaining homeostasis
Positive Feedback – reinforces current conditions
• Increases rate of change away from ideal value
• Continues until stressor is eliminated
Learning Target: Mechanisms of Homeostasis
Negative Feedback
e.g. CO2 level in blood
• Person holding their breath
• Sensors register ↑ CO2 levels in blood
• Send information to Control Center
(Medulla Oblongata) in brainstem
• Control center compares current values to ideal
• Determines action and sends instructions
through communication center (motor nerves)
• Diaphragm and ribcage (target) relax then
contract forcing you to take a breath.
Learning Target: Mechanisms of Homeostasis
Other common examples:
Negative Feedback
• Sweating when hot
• Evaporation of sweat cools down body with elevated
temperature
• Shivering when cold
• Heat production from muscle contractions warm cold
body temperature
• Drinking a 72 oz. Big Gulp
• Increase urination of excess fluids
• Eat a candy bar
• Insulin produced to take care of
excess sugar in blood
Learning Target: Mechanisms of Homeostasis
Positive Feedback
e.g. Childbirth
•
Learning Target: Mechanisms of Homeostasis
I Can… Explain how negative feedback mechanisms help
regulate and maintain a narrow range of internal conditions
in the human body among a wide range of external
conditions.
Learning Check √:
I Will…
Completion of
• List and define the components
Ch. 28. 2
of a control system
Study Guide WS
• Define feedback
• Explain how negative feedback works.
• Give an example of negative feedback in
the human body
• Give an example of positive feedback in
the human body