B2 – Keeping Healthy

B2.1 How do our bodies resist infection?

Ø Microorganisms are organisms that are really small and we can only see them using a microscope.

Ø An infectious disease is one which can be passed on from one person to another.

Ø Symptoms of an infectious disease are caused by damage done to cells by Microorganisms or the poisons (toxins) they produce

Ø Lifestyle diseases appear to increase in frequency as countries become more industrialised and people live longer e.g. asthma, diabetes, obesity etc.

Ø The three types of infectious diseases include:

1. Bacteria

2. Virus

3. Fungus

Ø Microorganisms (bacteria and viruses) require warm, moist conditions and nutrients present in order to reproduce rapidly to produce large numbers

Ø White blood cells are present in our immune system and fight off any Microorganisms entering the body.

Ø When microorganism enters the body, the antibodies produced by white blood cells detect the antigens that are stuck to the pathogen (microorganism) and stick to the foreign antigen markers to fight them off.

Ø The white blood cells produce phagocytes to engulf and digest the pathogen.

Ø Memory cells are then produced and they capture the disease so that next time when the same pathogen attacks again, antibodies will be produced faster to fight the disease.

Ø A different antibody is needed as different Microorganisms have different antigens.

B2.2 What are vaccines and how do they work?

Ø A vaccination is an injection which contains the dead or weak form of the disease.

Ø Since the disease present inside the injection is non-viral, the person being injected won’t be affected.

Ø Vaccinations provide protection from Microorganisms as the dead form of the microorganism is injected first so that the memory cells capture the disease and next time when the actual disease enters the body memory cells will remember therefore antibiotics will be produced faster to fight disease.

Ø It is important to vaccinate a high percentage of the population in order to prevent epidemics of infectious disease because if many people haven’t been vaccinated, they will be exposed to the infectious disease and therefore the infectious disease can spread through the general public.

Ø It is mainly the idea of herd immunity so that it won’t put a lot of strain on doctors or affect many other people.

Ø Vaccinations and drugs (medicines) can never be completely risk-free as some people can have different reactions to them or varying degrees of side effects.

Ø Due to our genetic differences, people react differently to vaccinations or drugs.

Ø Edward Jenner was a scientist and he discovered a cure for smallpox.

Ø Jenner injected the boy with cowpox and the boy had little fever but no great illnesses. The boy was then cured and he never infected with that virus again.

Ø Antibiotics are substances that kill or inhibit the growth of bacteria. They DO NOT work against viruses.

Ø Antibiotics either work by being bactericidal where they kill Microorganisms or by being bacteristatic where they inhibit the growth of Microorganisms.

Ø Antibiotics aren’t always successful as sometimes a mutation can occur in the DNA of a bacterium, making them resistant to the drug.

Ø This mutation gene can spread to the surrounding bacteria, thus making them resistant to the antibiotics.

Ø As the mutation gene spreads, more bacteria become resistant, multiply and thrive.

Ø In order to reduce the risk of antibiotic resistance, we should only use antibiotics when it is necessary and always complete the course when we’re prescribed with antibiotics.

Ø We mustn’t also take antibiotics more than necessary hence it can increase the chances of resistant bacteria.

Ø New drugs or vaccines are first tested for safety and effectiveness which are carried out in stages.

1. Stage 1 – human cells in a lab – safety and effectiveness

2. Stage 2 – animals – effectiveness

3. Stage 3 – Clinical trials

Ø On healthy human volunteers – safety

Ø On people with the illness – safety and effectiveness

Ø There are three types of human trials

1. Open-label – both doctor and patient know who’s taking the drug.

2. Blind – only the doctor knows who’s taking the drug

3. Double-blind – neither patient or doctor know who’s taking the drug

Ø Long term human trials are very important because it lets doctors know how effective and safe the drug can be and help them decide whether if it’s ready to be used as treatment for the general public.

Ø Ethical issues with placebos in human trials is that the patients still believe that the drug has effect and they’re not aware if they are treated with placebos.

B2.3 What factors increase the risk of heart disease?

Ø The human heart is described as a double pump because the left side of the heart pumps in oxygenated blood to the rest of body whereas the right side of the heart pumps out deoxygenated blood to the lungs.

Ø Heart muscle cells need their own blood supply because like other body cells, they need oxygen and food. The blood carries the oxygen and food to the heart muscle cells.

Ø Arteries have thick muscular walls in order to withstand high pressure of blood.

Ø Capillaries are thin-walled so it allows transport of gases and nutrients between cells and blood. They also connect veins and arteries together.

Ø Veins also have thin walls and they have one-way valve to keep the blood moving in the right direction.

Ø Veins carry deoxygenated blood from the rest of the body back to the heart and arteries carry oxygenated blood from the heart to the rest of the body.

Ø The pulmonary vein carries oxygenated blood from lungs to heart and the pulmonary artery carries deoxygenated blood from the heart to lungs.

Ø Valves prevent backflow of blood.

Ø Blood pressure measurements record the pressure of blood on the walls of the artery.

Ø A blood pressure measurement is given as two numbers, the higher value is when the heart is contracting and the lower value is when the heart is relaxed.

Ø The normal blood pressure for an adult is 120/80

Ø Heart rate and blood pressure can measure how hard your heart is working. You can measure your heart rate by taking your pulse.

Ø Fatty deposits building up in blood vessels supplying the heart muscle can result in a heart attack.

Ø Heart diseases can be caused by lifestyle factors or genetic factors.

Ø Lifestyle factors include; poor diet, stress, cigarette smoking, misuse of drugs etc.

Ø Although regular moderate exercises reduce the risk of developing heart disease.

Ø High blood pressure can also increase the risk of developing heart disease.

Ø Misuse of drugs can affect health, increasing risk of heart attack.

B2.4 How do our bodies keep a healthy water balance?

Ø Homeostasis is maintaining a constant internal environment e.g. Temperature or water balance.

Ø Our body needs to keep the correct levels of water and get rid of toxic waste products through excretion.

Ø In a control system, a receptor detects changes in the environment, a processing centre receives the information and responds automatically and an effector produces the response.

Ø Negative feedback is an action that detects changes in the system or in certain conditions and reverses the change.

Ø Water homeostasis controls the amount of water that you have in your body.

Ø Excretion removes toxic waste from your body.

Ø ADH, anti-diuretic hormone, is secreted from the pituitary gland.

Ø On a hot day you’re likely to drink lots of water and more ADH is secreted from the pituitary gland. As most of the water/fluid is lost through sweat, respiration and faeces, the kidney will reabsorb more water to balance the water content as a response to concentration of blood plasma and you will produce small quantities of concentrated urine.

Ø On a cold day you’re less likely to feel very thirsty so less ADH is secreted from the pituitary gland. Not a lot of water will be lost through sweat, respiration and faeces therefore kidney will reabsorb less water so you will produce less concentrated but large quantities of urine.

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