Biology Revision

Hormones are secreted by special glands and they are used to help control and co-ordinate processes that happen in your body.

The nervous system uses electrical impulses to enable you to react to your surroundings and co-ordinate what you do in them.

Cells called receptors detect stimuli (changes in the environment), these are located in sense organs.

They then send this response to the CNS in the brain and spinal cord through sensory neurones. They are then sent back to effector organs (muscles or glands) along the motor neurone.

Some responses to stimuli are automatic and require no thought process these are called reflex actions. They happen in a reflex arc are contain a sensory, motor and relay neurone.

Reflex actions run all the time are everyday bodily functions and help you to avoid danger.

When the electrical impulse reaches a synapse (junction) it has to release chemicals that diffuse across the gap and starts up a new impulse in the new neurone.

Hormones are used to control the menstrual cycle.

FSH is produced by the pituitary gland and makes eggs mature in the ovaries and stimulates the ovaries to produce oestrogen.

Oestrogen is made and secreted by the ovaries and stimulates the lining of the womb to build up for pregnancy. Inhibits production of FSH and stimulates pituitary gland to make LH.

LH secreted by pituitary gland stimulates the release of a mature egg from the ovaries roughly in the middle of the menstrual cycle.

Hormones can be used to control fertility.

Oral pills are taken to stop fertilization by stopping FSH being produced so no eggs can mature.

FSH can be given to women encourage mature eggs to be made and often these eggs can be used in IVF.

The ads and disads are that it does not always work and can lead to multiple pregnancies, it also raises ethical issues.

Humans need to maintain a constant internal environment (levels of water, ions, temperature and blood sugar)

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

Most people eat a varied diet which includes everything needed to keep the body healthy. If they do not have a balanced diet they will end up malnourished.

Different people need different amounts of energy, the more exercise you do the more energy you need to take in.

The metabolic rate is the rate at which all the chemical reactions take place in the body, this rate varies from person to person.

Any excess energy you take in will be stored as fat.

Obese people tend to have more health problems than people of normal weight.

People who do not eat enough are also at risk from serious health problems such as your immune system does not work as well and you become very thin and your muscles start to waste away.

Fast Food often contains high levels of fat and salt.

If you increase your fat levels your cholesterol in your blood also increases.

If you have high levels of cholesterol then it increases your risk of getting heart disease and blocked blood vessels.

Cholesterol is carries around the body by 2 types of lipoproteins - (LDLs and HDLs).

Low-Density Lipoprotein (LDL) carries cholesterol to your body cells from your liver.

High-Density Lipoprotein (HDL) carries cholesterol away from your body cells to your liver.

3 main types of fat (saturated - no carbon double bonds; mono-unsaturated - 1 carbon double bond; polyunsaturated - >1 carbon double bond)

Too much salt in your diet can lead to high blood pressure.