1. Homeostasis & Body Temperature National 4 &5 – Multicellular Organisms

2. Saving energy? James has decided to save energy by staying in bed all day. Surprisingly, the answer is only about 30%. How much of his energy do you think this will save? The other 70% keeps his body temperature at 37 °C, and the solutions around his cells at just the right concentration.

3.  By the end of this lesson, you will be able to:  Explain the term homeostasis  Explain why the body needs to maintain a constant core temperature  Explain some of the corrective mechanisms involved in temperature control Learning Outcomes

4.  The body uses so much energy, because it must maintain a constant internal environment.  This process of keeping things the same is called homeostasis.  A series of automatic control systems ensures the body maintains a constant temperature  - and steady levels of water, ions and blood sugar.  Homeostasis allows the body’s cells to work at their optimum. What is homeostasis?

5. Keeping comfortable

6.  Environmental temperature is constantly changing.  Despite this, the body must be kept at a constant temperature of 37 °C.  Why 37 o C?  - this is the optimum temperature for the body’s enzymes.  If body temperature falls too low  - reactions become too slow for cells to survive  If body temperature rises too high  - the body’s enzymes are at risk of denaturing. Why control temperature?

7.  The vital organs, such as the heart, liver and kidneys, are maintained at 37°C.  This is the core body temperature.  Skin temperature is usually lower than the core body temperature.  On a warm day, skin temperature may be just 1 °C lower than the core body temperature  - but on a very cold day it could be up to 9 °C lower. What is core body temperature?

8.  Core temperature is maintained by balancing heat gain and heat loss.  This is called thermoregulation  How can heat be gained?  - movement and exercise  - shivering  - vasoconstriction  - wearing extra clothing  How can heat be lost?  - sweating  - vasodilation  - removing extra clothing Finding the right balance

9. Too hot…or too cold?

10. Finding the right balance

11.  Body temperature is monitored and controlled by temperature receptors in the skin and brain.  These receptors detect changes in the temperature of blood.  The thermoregulatory centre in the brain is called the hypothalamus.  If body temperature deviates from 37 °C, the hypothalamus sends out electrical signals  - these trigger actions or behaviours that increase or decrease heat loss. How is temperature controlled? hypothalamus

12.  Overheating:  Sweating rate increases  Vasodilation  - increased blood flow to skin surface  Overcooling:  Sweating rate decreases  Vasoconstriction  - decreased blood flow to skin surface  Contraction of skin erector muscles (“goosebumps”)  - traps a layer of air next to skin  Shivering  - muscles generate heat  Increased metabolic rate e.g. liver Response to change in body temperature

13. Responding to change

14. Negative feedback in the body

15. Thermoregulation: true or false?