1. Homeostasis: Maintaining a Balance

2. Key Words: Maintain – keep up. Constant – the same. Internal – inside the body. Environment – surroundings of the body.

3. Body cells work best if they have the correct Temperature Water levels Glucose concentration Your body has mechanisms to keep the cells in a constant environment

4. Homeostasis: Homeostasis is the process by which organisms maintain their internal environment within tolerable limits, despite changes in their behavior and the external environment.

5. Living organisms need to control; Body temperature and metabolic rate Concentrations of dissolved salts and minerals Concentrations of nutrients, such as glucose in the blood Input and output of water Quantities of nitrogenous wastes Oxygen and carbon dioxide concentrations Removal of manufacturing cells of foreign substances

6. Homeostasis ensures that the organisms operates at maximum performance.

7. Homeostasis as a 2 stage process:  Homeostasis involves 2 distinct stages: 1.Detecting changes from the stable state: 2.Counteracting change:

8. Stage 1: Detecting changes from the stable state If our body temperature rises, the temperature rise in the blood stimulates the brains anterior hypothalamus (and inhibits the posterior hypothalamus). Alternatively, when a mammal is exposed to cold, skin receptors increase their activity, sending nerve impulses to the posterior hypothalamus. Plats detect gravity, light intensity and direction, and the length of the period of darkness

9. Stage 2: Counteracting changes from the stable state After detecting the rise on body temperature, the hypothalamus then stimulates heat loss by increasing blood circulation through the skin, increasing sweating and decreasing metabolic activity and muscular activity. This the body temperature is lowered. After detecting the drop in temperature, activity in the posterior hypothalamus stimulates the sympathetic nervous system to activate mechanism that conserve heat Plants may, after detecting increase in concentration of fluids, release abscisic acid from chloroplast so that there is a closing of stomates and an increase in the production of watertight resins.

10. Controlling 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 37 ºC

11. Controlling body temperature Animals with a large surface area compared to their volume will lose heat faster than animals with a small surface area.

12. Volume : Surface area ratio = 1:6 For every 1 unit of heat made, heat is lost out of 6 sides Volume : Surface area ratio = 1:5 For every 1 unit of heat made, heat is lost out of 5 sides

13. The bigger the Volume : Surface Area ratio is, the faster heat will be lost.

14. Why do we need to regulate the internal body temperature? To provide the optimum conditions for enzyme- catalysed reactions to be carried out.

15. Body Temperture: Normal internal body temperature is 37 0 C. Temperatures above this: denature enzymes and block metabolic pathways Temperatures below this: slow down metabolism and affect the brain.

16. 3 components of a feedback system: 1) receptor sensor that responds to changes (stimuli) 2) control centre sets range of values, evaluates input and sends output 3) effector receives output from control centre and produces a response

18. Body Temperature Control The hypothalamus acts as a thermostat and receives nerve impulses from heat and cold thermoreceptors in the skin. There are also receptors in the hypothalamus- called central thermoreceptors. These detect changes in blood temperature.

19. Correction of overheating 1.Detected by thermoreceptors in the hypothalamus. 2.Causes vasodilation. 3.Sweating

20. What mechanisms are there to cool down the body? 1.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.

21. Sweating The skin

22. Cooling Down When it's hot and you need to cool down, muscles at each hair relax. Hairs lie close to the skin. Air does not act as an insulating layer.

23. What mechanisms are there to cool down the body? 2 - 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!

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

25. Over-cooling Detected by thermoreceptors in the hypothalamus. Causes vasoconstriction. Decreased sweating Shivering/Piloerection

26. What mechanisms are there to warm the body up? 1 - 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.

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

28. 2 - Piloerection This is when the hairs on your skin “stand up”. 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 air becomes an insulating layer. What mechanisms are there to warm the body up?

29. Keeping Warm When it's cold, the muscle contracts pulls the hair up. A layer of warm air accumulates around the hair and insulates the organism. Heat retained

32. Homeostasis video: http://www.youtube.com/watch?v=XZxuQo3ylII