Homeostasis
Homeostasis: The dynamic steady state of
the constituents in the internal fluid
environment that surrounds and exchanges
materials with the cells

Maintaining a state of homeostasis is vital
to the survival of cells

Each cell, through specialized activities,
contributes as part of a body system to
the maintenance of homeostasis
Examples

Your body temperature rises above normal
levels, so it is no longer in homeostasis


Your body needs to be able to detect the
problem and respond (lower your body
temperature)
Your body doesn’t have enough water, so it is
no longer in homeostasis

Your body needs to be able to detect the
problem and respond (get more water)
Negative and Positive
Feedback

Negative feedback: A response that
opposes the change in environment
 Ex.
Sweating lowers our body
temperature after it has gotten too
high

Positive feedback: A response that
exaggerates the change in environment
 Ex.
Contractions during labor get more
frequent and intense as they go
Deviation in
controlled
variable
Homeostatic Response:
Negative Feedback
Detected by
Sensor
Informs
Integrator
Sends instructions to
Effector(s)
Brings about
Compensatory
Response
Leads to
Controlled
variable
returned to
normal
Deviation in
controlled
variable
Fall in room
temperature
below set point
Detected by
Detected by
Thermometer
Sensor
Informs
Informs
Integrator
Sends instructions to
Effector(s)
Brings about
Compensatory
Response
Leads to
Controlled variable
returned to normal
Thermostat
Sends
instructions to
Furnace
Brings about
Increased
heat output
Leads to
Increase in room
temperature to set point
Example:
Thermostat in
a room
Deviation in
controlled
variable
Rise in body
temperature
Detected by
Detected by
Hypothalamus
Sensor
Informs
Informs
Integrator
Sends instructions to
Effector(s)
Brings about
Compensatory
Response
Leads to
Controlled variable
returned to normal
Central Nervous System
Sends
instructions to
Sweat Glands
Bring about
Sweat to cool the body
Leads to
Evaporative cooling of
the body
Example: Rise
in body
temperature
The Hypothalamus

Part of the brain involved in regulating many things


Body temperature, thirst, urine output, food intake,
hormone secretion, uterine contractions, milk ejection,
emotional and behavioral patterns, etc.
A common sensor homeostatic pathways
Central Nervous System

Includes the brain and spinal cord

Integrates information from signals and the activity of
all body parts (it receives messages and then gives
orders for a response)

The most common integrator of homeostatic pathways
Decrease in
body fluids
Homeostatic Response:
Dehydration
Detected by
Informs
Sends instructions to
Higher integrative center of brain
Brings about
Leads to
Changed
behavior
(drink water)