1. Chemistry of Our World – The Human Body
HOMEOSTASIS

2. What is Homeostasis?
The ability of the Body to maintain a balanced internal environment that is within the normal range of health for that organism
The organism must have this balance in order to thrive and survive

3. How it all Works
Homeostasis involves a system of checks and balances to keep stability of the animal’s internal environment.
The skin, kidneys, liver, endocrine system, nervous system and sensory system all play a part in maintaining the internal environment within narrow limits

4. Regulated Factors in the Body
Some factors homeostatically regulated include:
Concentration of nutrient molecules (food)
Concentration of water, salt, and other electrolytes
Concentration of waste products
Concentration of O2 = 100mmHg and CO2 = 40 mmHg
Average pH = 7.35
Blood volume 4-6 L and pressure 120/80
Temperature = 37o C (98.6 F)
Heart Rate = Average bpm

5. Effects of Homeostasis
Homeostasis is continually being disrupted by
External stimuli
heat, cold, lack of oxygen, pathogens, toxins
Internal stimuli
Body temperature
Blood pressure
Concentration of water, glucose, salts, oxygen, etc.
Physical and psychological distresses
Disruptions can be mild to severe
If homeostasis is not maintained, death may result

6. Maintaining Control
In order to maintain homeostasis, the control system must be able to
1. Detect abnormalities from the normal range
2. Integrate this information with other body systems, external environmental factors, etc.
3. Make appropriate adjustments to restore the system to normal.

7. Control of Homeostasis

8. Two Types of Control
Feedforward - term used for responses made in anticipation of a change
Example: Salivation and release of extra stomach acid due to smell or sight of food
Feedback - refers to responses made after change has been detected
Two Types of feedback systems
Negative
Positive

9. Feedback Loops Negative feedback loop Positive feedback loop
original stimulus reversed
most feedback systems in the body are negative
used for conditions that need frequent adjustment
Examples: heart rate, blood pressure, temperature
Positive feedback loop
original stimulus intensified
seen during normal childbirth

10. The Process:

11. Example: Body Temperature
All mammals maintain a constant body temperature.
Human beings have a body temperature of about 37ºC.
E.g. If your body is in a hot environment your body temperature is 37ºC
If your body is in a cold environment your body temperature is still 37ºC

13. Examples
Sweating
When your body is hot, sweat glands are stimulated to release sweat.
The liquid sweat turns into a gas (it evaporates)
To do this, it needs heat.
It gets that heat from your skin.
As your skin loses heat, it cools down

14. Sweating
The skin

15. Examples Vasodilation
Your blood carries most of the heat energy around your body.
There are capillaries underneath your skin that can be filled with blood if you get too hot.
This brings the blood closer to the surface of the skin so more heat can be lost.
This is why you look red when you are hot!

16. This means more heat is lost from the surface of the skin
If the temperature rises, the blood vessel dilates (gets bigger).

17. Vasoconstriction This is the opposite of vasodilation
The capillaries underneath your skin get constricted (shut off).
This takes the blood away from the surface of the skin so less heat can be lost.