Homeostasis

HomeostasisMaintaining your inner environment

Examples of homeostasis:1. temperature (37C)2. pH of blood3. glucose level in blood4. water & salt content of blood

Why should these factors be kept constant?For enzymes to work effectively.

Homeostasis: maintaining a constant internal environment

Skin, our largest organ

Reminder: see controlling body temp animation.

Controlling your body temperature

To lower body temperature To raise body temperature

Blood vessels in the skin dilate to increase blood flow; increase heat loss by radiation.

Hair muscles relax; hairs lie down to trap less air around the body.

Sweat glands secrete more sweat that cools the body as it evaporates.

Blood vessels in the skin constrict to decrease blood flow; decrease heat loss by radiation.

Hair muscles contract; hairs stand upright to trap more air around the body.

Sweat glands secrete less sweat that cools the body as it evaporates.

Muscles “shiver” to produce more heat.

Chemical reactions in liver increase to generate more heat.

Surface area: volumeAs an organism increases in size its surface area to volume ratio decreases.

1cm

Volume A=1x1x1 =1cm3

Surface area= 6x1cm2 =6cm2

Ratio 6:1

10 cmVolume A=10x10x10 =1000cm3

Surface area= 6x100cm2

=600cm2

Ratio 600:1000 0.6:1

AB

Which looses more heat, small or large animals?

Small because they have a larger S.A:V ratio

How does surface area:volume affect an organism?

They curl up/cuddle together They have higher metabolic rates to release

more heat

What do small animals do to keep their warmth?

Have less fur on their bodies e.g. elephant Elephants also have large ears that contain

a great amount of blood vessels, flapping their ears helps them to lose more heat

Have more “baths” e.g. hippopotamus

What do large animals do to keep their cool?

When blood glucose level is high:

Liver takes up glucose & changes it to glycogen (stored in liver cells)

Controlling blood glucose level

Insulin

When blood glucose level is low:

Liver breaks down glycogen & changes it to glucose(released into blood stream)

Glucagon

To keep blood glucose level, body temperature constant they are controlled by a negative feedback system.

Negative feedback control results in reversal of the action taking place.

e.g. after insulin hormone secretion and the consequent removal of glucose from blood, the blood sugar falls below normal & glucagon is produced to bring it back up.

Negative feedback