1. Homeostasis and Human Body Systems
Miss Richardson
SBI4U

2. How would you feel if you were here?

3. How would you feel if you were here?

4. How would you feel?
South Pole, <41°C

5. Homeostasis
… is the tendency of the body to maintain a constant internal environment
This is done through regulating various systems
Human body:
body temp: 37⁰C
blood pH: 7.3 – 7.4
Blood sugar: 5mmol/L blood

6. Feedback Systems
The body maintains homeostasis through feedback systems
Feedback systems consist of three components:
Receptor/sensor – detect the stimuli/change in internal environment and send signal to control centre
Integrator/Control Centre – receives information and takes appropriate action
Effector – cause change and make a response to change conditions

7. Negative Feedback Systems
Most homeostatic mechanisms in animals use negative feedback systems to operate
Negative Feedback Systems:
brings the system back to its original state
If a level increases, the body works to decrease it
If a level decreases, the body works to increase it
Example:
When you exercise, your muscles produce heat, raising your body temperature
Signals are sent to control centre to induce sweating and dilation of blood vessels
Results in heat loss through radiation and conduction

8. Why does the body need to regulate temperature?
Human enzymes work best at 37°C.
The hypothalamus is a part of the brain that detects change in internal body temperature.
Thermoregulation is the process of regulating body temperatures
When we are hot:
Erector muscles in skin relax, allowing hairs to lie flat so the body is less insulated
Vasodilation – blood capillaries near the skin’s surface get wider, and more blood flows near skin surface
allows for more heat loss due to radiation
Sweat glands secrete – allows for cooling due to evaporation

9. Thermoregulation When we are cold:
Shivering – muscles contract and relax quickly to release heat
Rate of cellular respiration increases to release heat and energy
Vasoconstriction – blood capillaries near skin surface narrow to keep blood near the core of the body and conserve heat
Hairs on skin stand up – erector muscles contract, allowing more air to be trapped between hairs to act as insulating layer
Sweat secretion is reduced

10. Thermoregulation

11. Positive Feedback Systems
moves system further from the steady state
Example:
In labour, a woman’s uterine muscles contract, triggering production of oxytocin
Oxytocin increases strength of contractions

12. Feedback Systems Other examples of positive feedback systems include:
Platelets – when platelets clump to form blood clots that signals more platelets are activated
Lactation – when breastfeeding, the more the baby suckles the more milk is produced
Estrogen – during follicular phase it causes the thickening of the uterine lining
Nerve signals – Na+ channels open when stimulated, this causes more Na+ channels to open resulting in an action potential