1. EXCRETION
HOMEOSTASIS

2. What is Homeostasis?
Homeostasis is the regulation of conditions in the body such as temperature, water content and carbon dioxide levels.
Diabetes is a condition where the body cannot regulate its blood glucose levels.

3. The conditions inside our body must be very carefully controlled if the body is to function effectively. 
Homeostasis is the maintenance of a constant internal environment.
The nervous system and hormones are responsible for this.

4. Examples of Homeostasis
Body temperature
This is controlled to maintain the temperature at which the body’s enzymes work best, which is usually 37°C.

5. Blood sugar level
This is controlled to provide cells with a constant supply of glucose for respiration.
It is controlled by the release and storage of glucose, which is in turn controlled by insulin.

6. Urine production in kidneys
Water content This is controlled to protect cells by stopping too much water from entering or leaving them. Water content is controlled by water loss from:
Urine production in kidneys
The Body
Sweating
The Skin
Exhalation
The Lungs

7. Negative feedback
WHAT IS THAT?

8. Negative feedback
Homeostatic control is achieved using negative feedback mechanisms:
if the level of something rises, control systems reduce it again
if the level of something falls, control systems raise it again

9. NEGATIVE FEEDBACK
FLOW CHART

10. Regulating body temperature
The human body is designed to function most efficiently at 37ºC. If you become too hot or too cold, there are ways in which your body temperature can be controlled.

11. Too hot When we get too hot:
Sweat glands in the skin release more sweat. The sweat evaporates, removing heat energy from the skin.
Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost.

12. Too cold When we get too cold:
Muscles contract rapidly - we shiver. These contractions need energy from respiration, and some of this is released as heat.
Blood vessels leading to the skin capillaries become narrower - they constrict - letting less blood flow through the skin and conserving heat in the body.

13. The skin The hairs on the skin also help to control body temperature.
They lie flat when we are warm, and rise when we are cold.
The hairs trap a layer of air above the skin, which helps to insulate the skin against heat loss.

14. The hypothalamus is the part of the brain which monitors the body's temperature.
It receives information from temperature-sensitive receptors in the skin and circulatory system.

15. The hypothalamus responds to this information by sending nerve impulses to effectors to maintain body temperature.
For example, if we become too cold, the hair erector muscles contract.
This raises the skin hairs and traps a layer of air next to the skin.

16. Skin hairs lie flat when we are hot and stand upright when we are cold

17. NEGATIVE FEEDBACK FOR TEMPERATURE REGULATION

18. Vasoconstriction and vasodilation
Too cold
Too hot
Process
Vasoconstriction
Vasodilation
Arterioles
Get narrower
Get wider
Blood flow in skin capillaries
Decreases
Increases
Heat loss from skin
Vasoconstriction and vasodilation
The amount of blood flowing through the skin capillaries is altered by
vasoconstriction and vasodilation.

19. Regulating blood glucose
Glucose is needed by cells for respiration.
It is important that the concentration of glucose in the blood is maintained at a constant level.
Insulin is a hormone - produced by the pancreas - that regulates glucose levels in the blood.

20. Action of Insulin Low glucose High glucose Effect on pancreas
Insulin not secreted into the blood
Insulin secreted into the blood
Effect on liver
Does not convert glucose into glycogen
Converts glucose into glycogen
Effect on blood glucose level
Increases
Decreases

21. High levels of Glucose

22. Low levels of Glucose