Responding to change
The body must respond to internal and external conditions.
- You have glands that produce hormones. The hormones are transported around your body by the blood.
- Electrical impules pass along the nervous system.
- All respones must be co-ordinated
Examples of sensory organs:
- Eyes - sensitive to light
- Ears - sensitive to sound
- Skin - sensitive to touch, pressure, pain and temperature
- Nose and tongue - sensitive to chemicals
Here are the steps involved in a reflex action:
- A receptor detects a stimulus (e.g. a sharp pain)
- A sensory neurone transmits the impulse.
- A relay neurone passes the impulse on.
- A motor neurone is stimulated.
- The impulse is sent to the effector (muscle or gland).
- Action is taken
At the junction between two neurones is a synapse. Chemicals transmit the impulse across the gap.
The menstrual cycle
- FSH is made by the pituitary gland and causes the egg to mature and oestrogen to be produced.
- Oestrogen is produced by the ovaries and inhibits the further production of FSH. It stimulates the production of LH and also stimulates the womb lining to develop to recieve the fertilised egg.
- LH is made by the pituitary gland and stimulates the mature egg to be released.
The artifical control of fertility
- The contraceptive pill contains oestrogen. This prevents the production of FSH so no eggs can mature.
- If a woman cannot produce mature eggs then FSH can be given. This is known as "fertility treatment."
Steps of IVF (in vitro fertilisation)
- Fertility drugs are used to make lots of eggs mature at the same time for collection.
- The eggs are collected and placed in a special solution in a petri dish.
- A sample of semen is collected.
- The egg and sperm are mixed in a petri dish.
- The eggs are checked to make sure they have been fertilised and the early embryos are developing properly.
- When the fertilised eggs have formed tiny balls of cells, 1 or 2 of the tiny embryos are placed in the uterus of the mother. Then, if all goes well, at least one baby will grow and develop successfully.
Internal conditions that are controlled include:
- water content
- ion content
- blood sugar level
Water is leaving the body all the time as we breathe out and sweat. We lose any excess water in the urine (produced by the kidneys). We also lose ions in our sweat and in the urine.
We must keep our temperature constant otherwise the enzymes in the body will not work properly (or may not work at all).
Sugar in the blood is the energy source for cells. The level of sugar in our blood must be controlled.
Diet and excersise
Food provides the energy that your body needs to carry out it's activities.
If you excersise you will need more energy.
Excersise increases the metabolic rate. This is the rate at which your body uses energy needed to carry out chemical reactions.
If it is warm you will need less energy than when it is cold.
The amount of energy you need depends on many things. For example:
- your size
- your sex
- the amount of excersise you do
- outside temperature
If you take in more energy (food) than you need you will become fat.
If you are very fat you are said to be obese.
Obese people are likely to suffer more from:
- arthritis (worn joints)
- high blood pressure
- heart disease.
If you take in less energy than you will loose weight.
In developing countries some people have health problems linked to too little food. These include reduced resistance to infection and irregular periods in women.
Fast food can contain too much salt and fact.Too much salt can lead to increased blood pressure.
Cholesterol is made by the liver and the amount made depends upon diet and inherited (genetic) factors. We need cholestrol, but too much in the blood leads to an increased risk of disease of the heart and blood vessels.
Two types of lipoproteins carry cholesterol around the body:
- low density lipoproteins (LDLs) which are bad and can cause diseases
- high density lipoproteins (HDLs) which are good for you.
Saturated fat in your diet increases your cholestrerol level.
Mono-unsaturated and polyunsaturated fats help reduce cholesterol levels. We can use statins to stop the liver producing too much cholesterol.
Useful drugs made from natural substances, have been used by indigenous people for a very long time.
When we develop new drugs to help people, we have to test them over a long time to make sure that there are no serious side effects.
- Thalidomide was used as a sleeping pill and to prevent morning sickness in pregnant women. It had very serious side effects on fetuses developing in the womb. It is now used to help cure leprosy.
- Recreational drugs are used by people for pleasure.
- Heroin and cocaine are recreational drugs. They are very addictive and illegal.
- Cannabis is a recreational drug. It is also illegal. It is argued that using cannabis can lead to using "harder" drugs.
- If you try to stop taking addictive drugs you will suffer withdrawal symptoms.
Legal and illegal drugs
Medicinal drugs are developed over many years and are used to control disease or help people that are suffering. Many medicinal drugs are only available on prescription from a doctor. Recreational drugs are used only for pleasure and affect the brain and the nervous system.
Recreational drugs include cannabis and heroin which are both illegal. As recreational drugs affect the nervous system it is very easy to become addicted to them. Nicotine and caffeine (in coffee and coke) are legal drugs which are used recreationally, alcohol is also legal for people over the age of 18 in this country. Some drugs which are used for medicinal purposes can be used illegally, e.g. stimulants used by sports people.
Alcohol - the acceptable drug?
- Alcohol slows down the nervous system and therefore slows down your reactions. This will cause problems when driving.
- Too much alcohol leads to loss of self control.
- Drinking too much alcohol may cause a person to lose consciousness or go into a coma.
- The use of alcohol over a long time will damage the liver (cirrhosis) and brain.
Smoking and health
- It is not illegal to smoke tobacco over the age of 16 years.
- The nicotine in tobacco smoke is addictive.
- Tobacco smoke also contains cancer causing chemicals.
- The carbon monoxide in tobacco smoke reduces the amount of oxygen the blood can carry.
- Pregnant women who smoke have babies with lower birth weights, as the babies do not get enough oxygen.
- Pathogens cause infectious disease.
- Some bacteria and viruses are pathogens. These bacteria and viruses reproduce inside the body producing poisons (toxins) that make us feel ill.
- Semmelweiss discovered that infection could be transferred between patients in a hospital. He said that washing your hands between treating patients helped stop the transfer of infection. However, it was many years before other doctors took his ideas seriously.
White blood cells do three things to help us protect ourselves:
- They can ingest pathogens. This means that they digest and destroy them.
- They produce antibodies to help destroy particular pathogens.
- They produce antitoxins to counteract (neutralise) the toxins that pathogens produce.
Using drugs to treat disease
- Antibiotics kill inefective bacteria in the body. Penicillin is a well known antibiotic.
- Viruses are much more difficult to kill, as they live inside the cells.
- Painkillers make you feel better, but do nothing to get rid of the disease causing the pain.
The MRSA "super bug" is a bacterium that has evolved in hospitals through natural selection. It is resistant to commonly used antibiotics.
Some pathogens, particularly viruses, can mutate resulting in new forms.
Very few people are immune to these new pathogens and so disease can spread quickly within a country (epidemic) or across countries (pandemic).
Developing new medicines
It costs a lot of money to develop a new medicine. It also takes a long time. New medicines must be tested to see if they are toxic (poisonous) and to see if they are effective (cure the disease). This work is carried out in laboratories (on animals) and on human volunteers.
If these tests are not thorough enough then a new medicine may have dangerous side effects. Thailidomide is a medicine that was used widely in the 1950s as a sleeping pill. It also helped to prevent "morning sickness" in a pregnant women. It was not tested thoroughly enough and women started to give birth to babies with abnormalities. It is not now used with pregnant women but is proving an effective treatment for leprosy.
- Dead or inactive forms of an organism can be made into a vaccine. Vaccines can be injected into the body.
- The white blood cells react by producing antibodies. This makes the person immune and prevents further infection, as the body responds quickly by producing more antibodies.
- There is an argument over whether some vaccines are completely safe, e.g. the MMR (measles, mumps and rubella) vaccine.