Homeostasis & Body Temperature

National 4 &5 – Multicellular Organisms

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.

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

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?

Keeping comfortable

Environmental temperature is constantly changing.

Despite this, the body must be kept at a constant temperature of 37 °C.

Why 37oC? - 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?

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?

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

Too hot…or too cold?

Finding the right balance

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

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

Responding to change

Negative feedback in the body

Thermoregulation: true or false?