Homeostasis refers to the physiological processes that regulate the internal environment of the body to maintain stable conditions suitable for life. Negative feedback mechanisms detect changes and trigger responses to counteract the change and return conditions to the set point. For example, thermoregulation uses sensors in the skin to detect temperature changes and effectors like sweating or shivering to cool or warm the body and maintain a core temperature around 37°C.

1. Homeostasis
Basic feedback mechanisms and Thermoregulation

2. Homeostasis =
The physiological state of the body in which
internal physical and chemical conditions are
kept within a range that is suitable for life
processes
Not steady
state, but often
described as a
balancing act

3. Normal body temperature : 37 C
Human cells need 35 C – 37.8 C in order
to function
Organisms survival depends on the
bodies ability to maintain an
internal environment
The extracellular fluid, which consists
of the interstitial fluid filling spaces
between cells and tissues and the
plasma or fluid portion of our blood

4. Sensor
(tissue/organs that
detect change)
Integrator
(processing / control center)
The Effector
(the system which
The returns body to
Response measured condition)

5. Homeostasis Mechanisms
Responsible for maintaining homeostasis in response to internal or
external environmental changes
Used to evaluate the environment and conditions, and take corrective
actions
Nervous system
External Internal
influences influences
Endocrine system

6. Negative Feedback Mechanisms
- Primary mechanism
- Stimulus resulting from a change in the external or
internal environment triggers a response that
compensates for the change
- To bring internal conditions back into balance, negative
feedback mechanisms use antagonistic effectors
- Antagonistic = they act to produce the opposite effect
of the change recorded by the sensor

7. Negative Feedback
Stimulus
(enviromental Systems
change)
Sensor
(ie: nerve
ending in skin)
Integrator
(ie: the Brain)
Effector
The response of the (muscle or
system cancels or gland)
counteracts the effect
of the original
environmental change Response
(system’s
output)

8. Integrator
(ie: the Brain)
The Set Point Environmental
Conditions

10. Examples

11. Experiment Time
 In a clean glass jar place several ants, cover with
a lid
 Submerge half the jar in ice/ice water
 Place hands around the upper portion of the jar
 After 5-15 minutes the ants will have moved
close to warm hands to attempt to maintain
homeostasis

12. Positive Feedback
 Feedback mechanism
 Increases the change in environmental conditions
 Usually do not result in homeostasis
 Ie: the release of adrenaline when an animal is
attacked

13. Thermoregulation
 Based on negative feedback
 Absorb thermal energy if they are cooler than
environment
 Release thermal energy if they are warmer than
environment
sweat

14. Conduction
= flow of energy when they come in contact with a
colder or warmer body