1. Introduction to Homeostasis

2. What is Homeostasis?
The tendency of the body to maintain a relatively constant internal environment
Homeostasis is critical for survival. Humans (similar to other vertebrates) survive within a narrow range of (optimal) conditions
Analogy: think of what a car engine needs to function properly: it needs fuel, it needs to be an acceptable temperature, and sometimes parts need to be replaced.

3. What is Homeostasis?
When we talk about our “internal environment” in homeostasis, we are referring specifically to the extracellular fluid [ECF] (fluid outside our cells)
The ECF can change in volume, temperature, chemical composition, etc.
These changes are constantly monitored (by sensors in our body which ‘communicate’ with the brain) so that a constant level can be maintained.

4. Homeostasis Examples
As you move higher, you begin breathing more rapidly as the concentration of oxygen in the air begins to decrease.
You have been working very hard expending enormous amounts of energy driving one leg in front of the other, and you find your body seeming to crave food.
You feel your pulse and notice that your heart is beating more rapidly pumping blood through your body in an effort to supply your cells with more oxygen and energy from the food. All of these are ways of your body trying to achieve stability.

5. How Are Changes in the Body Monitored?
(sensors
and receptors) – detect
Changes in
environment)
Control Centre
(mainly
the hypothalamus or
medulla oblongata)
sets a range of values within
which variables should
be maintained.
Regulator
(effectors) - receives
Signals from control
centre)

6. Feedback Mechanisms Positive Feedback
Receptors in the body constantly monitoring your internal environment.
Once a certain set point is reached, a message is sent to turn on or off pathway [temporarily].
Positive Feedback
Strengthens or increases a change in a variable
Negative feedback
Reverses the change detected in a variable so that the variable is brought back within a normal range

7. Positive Feedback Example

8. Positive Feedback Example
What happens during child birth?
Monitor: the head of the baby pushes on the cervix
Control Centre: the hypothalamus (in the brain) processes this information, causing the release of oxytocin (hormone)
Effector: Oxytocin targets the uterus to contract more to help push the baby out
Result: the increase of one variable (pressure on the cervix) causes the increase of another variable (release of oxytocin hormone) which causes contractions to increase more

9. Negative Feedback Example

10. Negative Feedback Example
What happens when you are in a cold environment?
Monitor: thermoreceptors detect a decrease of temperature
Control Centre: the hypothalamus (in the brain) processes this information
Effector: Skeletal muscles contract, shivering generates energy production to increase temperature
Result: the decrease of one variable (external temp) causes the increase of another (body temp)