B1 Homeostasis

This is a big topic and lends itself to questions worth a lot of marks.

So, what is homeostasis?

Well the, homeostasis is where the conditions inside the body are kept the same. It is all about keeping the internal environment the same regardless of what is happening.

There are 3 main things that you need to know how they are controlled.

1. Water - osmoregulation.
2. Temperature - thermoregulation.
3. Glucose - Blood glucose regulation.

Basically, water is to do with your sweat glands, kidneys and urine. Temperature is to do with your skin, sweating and blood vessels and glucose is about your pancreas and liver.

But, and it's a big but, you have to learn the various diagrams that go along with these 3 things to control. So let's start with water control.

You lose water by breathing and sweating. You also lose water in urine. If you drink too much water then your kidneys will produce more dilute urine - obviously. If you do not drink enough water then you will produce less urine and your brain tells you that you are thirsty. Again, common sense really.

Now, thermoregulation is a big topic to learn and you must include the diagrams that show what the skin does when you are hot or cold. Your body works best at 370C which is the optimum temperature for many chemical reactions and enzymes to work. Your body under the control of the hypothalamus which is a small part of the brain that monitors temperature.

So, what happens then?

When you are cold:

1. The hypothalamus causes muscles to shiver. This makes heat which warms you up.
2. The hypothalamus also causes erector muscles in the skins dermis to contract. This causes the skin hairs to stand up. This traps a layer of air for insulation. Note: it traps air not eat!
3. The hypothalamus constricts the blood vessels called capillaries near the skins surface. This means that less warm blood is near the surface so you lose less heat to the air. The fancy word for this is vasoconstriction.

When you are warm:

1. The hypothalamus causes sweating. You use heat to evaporate the sweat and so you cool down.
2. The hypothalamus increases the amount of blood flow to the blood vessels - capillaries - near the surface of the skin. I does this by making the blood vessels wider, it dilates them, so more warm blood flows near the surface of the skin so more heat is lost to the air - so you cool down. This is called vasodilation.

                                                Vasoconstriction                  Vasodilation


Diagram of the skin

Note where the sweat gland, capillary and hair is.

Negative feedback.

The control of body temperature is an example of negative feedback. This means that if you get too hot your body will work to make it colder, and if your are too cold then your body will make it warmer. All this, remember, is under the control of the hypothalamus and it is happening all the time without you thinking about it.