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Homeostasis


A day at the sauna

How does the body react to change?


Saving energy?

Sayid has decided to save energy by staying in bed all day.

How much of his energy do you think this will save?

Surprisingly, the answer is only about 30%. The other 70%

keeps his body temperature at 37°C, and the fluid

surrounding around his cells at just the right concentration.


What is homeostasis?

The body uses so much energy, even during sleep, because

it must maintain a constant internal environment.

This process of keeping things the

same is called homeostasis.

Nervous and hormonal control

systems ensure that the body

maintains a constant temperature.

These control systems also make

sure that the body has steady levels

of water, ions and blood sugar.

Homeostasis allows the body’s cells and enzymes to work at

their optimum level.


Maintaining internal conditions


Control systems


The organs of homeostasis


Why control temperature?

Environmental temperature is

constantly changing. One minute it can

be very hot, the next very cold.

Even slight changes in body temperature can have a life-

threatening effect on health. If body temperature falls too low,

reactions become too slow for cells to survive: too high, and

the body’s enzymes are at risk of denaturing.

Despite this, the body must be kept at

a constant temperature of 37°C.

Why?

This is the optimum temperature for the

body’s enzymes.


What is core body temperature?

The vital organs located deep within the body, such as the

heart, liver and kidneys, are maintained at 37°C. This is

the core body temperature.

Skin temperature at the body's

extremities, such as the fingers

and toes, is usually lower than

the core body temperature.

This reduces the energy lost.

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.


Measuring body temperature


Finding the right balance


Too hot…or too cold?


How is temperature controlled?

Body temperature is monitored and controlled by temperature

receptors in the skin and brain.hypothalamus

These receptors detect changes

in the temperature of blood

flowing through those areas.

The thermoregulatory centre in the

brain is called the hypothalamus.

If body temperature deviates from 37°C, the hypothalamus

and skin receptors send out electrical signals that trigger

actions or behaviours that increase or decrease heat loss.


Maintaining the core temperature


Why do we shiver?

When core body temperature drops, muscles begin to twitch.

This rapid contraction and relaxation of the muscles is

called shivering.

Shivering generates heat, which raises body

temperature.

Goosebumps involuntarily appear when a

person becomes cold. Goosebumps are

caused by the tiny muscles at the base of

body hairs pulling the hairs erect.

The upright hairs trap an insulating layer

of air, which helps reduce heat loss.


The structure of the skin


Vasoconstriction and warming up

Why do people go pale when they are cold?

Vasoconstriction is

caused by contraction

of the muscular wall of

the blood vessels.

When core body temperature falls, blood vessels in the skin

get narrower. This is called vasoconstriction.

This reduces the volume

of blood flowing near the

skin surface, and

reduces the amount of

heat lost from the body.


Vasodilation and cooling down

Why do people turn red when they are hot?

Additional cooling occurs with

the production of sweat from

sweat glands.

Vasodilation allows a larger volume of blood to flow near the

skin surface, transferring heat to the environment. This cools

the body down.

When core body temperature rises, blood vessels in the skin

get wider. This is called vasodilation.

As the sweat evaporates it

transfers heat away from the body.


Responding to change


Negative feedback in the body


Thermoregulation: true or false?


Glossary


Multiple-choice quiz

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