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SECTION 1: NERVES AND HORMONES.

The Nervous System

The nervous system allows the body to respond to changes in the environment. This process is
usually co-ordinated by the brain. Reflex actions are quick responses to stimuli (things that set off
reactions in the nervous system).

Receptors ­ this is a…

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Reflex Actions
When you stimulate a receptor, a signal is sent to the CNS and the brain then co ordinates a
response, but sometimes a very quick response is needed that doesn't need the involvement of the
brain, this is a reflex action. They happen without us thinking.

E.g. If…

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Radial muscles of the iris contract.
Circular muscles of the iris relax.
More light enters the eye through the dilated pupil.





Hormones

One of the functions of the blood is to transport dissolved substances (including hormones) around
the body. Hormones are chemical substances that help regulate the many processes in…

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Regulating Glucose in Blood

Glucose is needed by cells for respiration. It is essential that the concentration of glucose in blood
is maintained at a constant level. Insulin is a hormone produced by the pancreas that regulates
glucose levels in the blood.
Glucose Level Effect on Pancreas Effect on Liver…

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Diabetes
Diabetes is a disorder in which the blood
glucose levels remain too high. The pancreas doesn't produce insulin, meaning the blood sugar
levels increase to levels where you could go into a coma. It can be treated by injecting insulin. The
extra insulin allows the glucose to be taken…

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The hormone oestrogen is secreted by the ovaries. Oestrogen makes two things happen:

1. it stops FSH being produced - so that only one egg matures in a cycle
2. it stimulates the pituitary gland to release the hormone LH
The hormone LH causes the mature egg to be released…

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Enzymes are
important
because
chemical
reactions
would
happen too
slowly at
body
temperature
(37 degrees Celsius) if we did not have them
Temperature affects enzymes:
If the temperature decreases, the rate of reactions slows because the enzymes and other
molecules collide less often.
If the temperature is too hot, the…

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Cooling down

Sweat glands produce more sweat when we are hot because it cools us down when it evaporates
off the skin. Water lost through sweating must be replaced otherwise it could lead to dehydration.
In humid climates, sweat does not evaporate, so it does not help cool you down.…

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