HomeostasisWe Are Learning Today: The mechanisms by which the body

maintains a constant internal environment

Starter: Sports drinks Why do runners drink these rather

than just water? What do the labels claim they can do? Do you think these claims are true or

are they just a good way for drinks manufacturers to make quick money?

Homeostasis Humans need to maintain a constant

internal environment, controlling levels of water, blood sugar and temperature.

Homeostasis is the result of the coordination of your nervous system, your hormones and your body organs.

Thermoregulation:What organs are involved?

Hypothalamus

Muscle

Thermoregulation:Controlling temperature

This is controlled to maintain the temperature at which enzymes work best.

If you get too hot:

Hair muscles relax; hairs lie flat so letting more heat out.

Evaporation of sweat secreted by sweat glands cools skin.

Capillaries dilate, blood flow increases at the surface of the skin causing heat to be lost by radiation.

Thermoregulation:Controlling temperature

If you get too cold:

Hairs muscles pull hairs on end, trapping a layer of air which acts as an insulator.

Sweat glands stop secreting sweat.

Capillaries close to surface constrict, to allow less blood to flow.

Muscles shiver, generating heat.

OsmoregulationWhat organs are involved?

Hypothalamus

Pituitary gland

Kidney

Osmoregulation:Controlling water

InputsWater content in:•Drinking•Digestion

Water made in:Cellular respiration

OutputsWater content in:•Urine•Breathing•Sweating•Bowel movement

Check your learning

1. How might you expect the volumes in the above table to change on:

• A very hot day• A very cold day

Osmoregulation: Controlling water

Too little water in the blood

Detected by the hypothalamus

More ADH released into the blood by the pituitary gland

Kidneys absorb less water from the blood

So less water is lost in urine (urine is more

concentrated)

Blood water level returns to normal

Place the sequence of events in order:

Too little water in the blood

Detected by the hypothalamus

More ADH released into the blood by the pituitary gland

Kidneys absorb less water from the blood

So less water is lost in urine (urine is more concentrated)

Blood water level returns to normal

Glucoregulation – Controlling blood sugar levels

Liver

Pancreas

Glucoregulation

It is important that the concentration of glucose in the blood is kept at a constant level.

Glucose is a sugar needed by cells for respiration.

Insulin is secreted by the pancreas to control sugar level.

What is insulin? Insulin is a hormone which affects your

metabolism and other body functions.

Insulin causes cells in the liver, muscle, and fat tissue cells to take up glucose from the blood, storing it as glycogen in the liver and muscle, and stopping use of fat as an energy source.

When insulin is absent (or low), glucose is not taken up by body cells, and the body begins to use fat as an energy source.

Glucoregulation – Controlling blood sugar levels

Blood with too much glucose in it

Insulin injected by the pancreas

More glucose absorbed by tissues and the liver

Blood glucose reduced

Place the sequence of events below in order:

Blood with too much glucose in it

More glucose absorbed by tissues and the liver

Insulin injected by the pancreas

Blood glucose reduced

Team Challenge

Complete the word loop first to win the

prize!