1. Homeostasis

2. What is Homeostasis? What is Homeostasis? Homeo = SIMILAR Stasis = CONDITION Homeo = SIMILAR Stasis = CONDITION Homeostasis is a maintenance of constant ENVIRONMENT in the body. Homeostasis is a maintenance of constant ENVIRONMENT in the body. Body cells work best if they have the correct Body cells work best if they have the correct Temperature Temperature Water levels Water levels Glucose concentration Glucose concentration Your body has mechanisms to keep the cells in a constant environment. Your body has mechanisms to keep the cells in a constant environment. Homeostasis is a state of EQUILIBRIUM Homeostasis is a state of EQUILIBRIUM

3. What is Homeostasis? The maintenance of a constant environment in the body is called Homeostasis

4. What is Negative Feedback? A reaction that responds to reverse the direction of change is Negative Feedback

5. Controlling body temperature All mammals maintain a constant body temperature. All mammals maintain a constant body temperature. Human beings have a body temperature of about 98.6ºF or 37ºC. Human beings have a body temperature of about 98.6ºF or 37ºC.

6. What mechanisms are there to cool the body down? 1. Sweating When your body is hot, sweat glands are stimulated to release sweat. When your body is hot, sweat glands are stimulated to release sweat. The liquid sweat turns into a gas (it evaporates) The liquid sweat turns into a gas (it evaporates) To do this, it needs heat. To do this, it needs heat. It gets that heat from your skin. It gets that heat from your skin. As your skin loses heat, it cools down. As your skin loses heat, it cools down.

7. Sweating The skin

8. What mechanisms are there to cool the body down? 2. Vasodilation Your blood carries most of the heat energy around your body. 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. 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 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! This is why you look red when you are hot!

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

10. What mechanisms are there to warm the body up? 1. Vasoconstriction This is the opposite of vasodilation This is the opposite of vasodilation The capillaries underneath your skin get constricted (shut off). 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. This takes the blood away from the surface of the skin so less heat can be lost.

11. If the temperature falls, the blood vessel constricts (gets shut off). This means less heat is lost from the surface of the skin

12. What mechanisms are there to warm the body up? 2. Piloerection This is when the hairs on your skin “stand up”. This is when the hairs on your skin “stand up”. It is sometimes called “goose bumps” or “chicken skin”! It is sometimes called “goose bumps” or “chicken skin”! The hairs trap a layer of air next to the skin which is then warmed by the body heat The hairs trap a layer of air next to the skin which is then warmed by the body heat The air becomes an insulating layer. The air becomes an insulating layer.

13. Trapped Air This air insulates and warms the skin.

14. THINK ABOUT THIS How does warm the body? How does warm the body? SHIVERING How is this an example of NEGATIVE FEEDBACK? How is this an example of NEGATIVE FEEDBACK?

15. Positive feedback set point levels increase levels decrease further increase further decrease positive feedback In positive feedback, a deviation from normal conditions is amplified, leading to a further deviation. Positive feedback is rare in biology because it tends to produce harmful, unstable conditions. In early childbirth the release of the hormone oxytocin stimulates uterine contractions. The contractions trigger a positive feedback reaction. More oxytocin is released, initiating more contractions.

16. Visualizing homeostasis