Biology Chapter B2

1. The Heart

1.1. Your body’s supply route Your heart is a bag of muscle in your body. When you are sitting down it beats at about 70 beats per minute. It has four chambers. The upper two receive blood and the lower two have thick muscular walls to pump the blood. Your heart is a double pump. Tubes carry the blood around your circulatory system.

1.2. How blood circulates Blood enters the right-hand side of your heart from your body. It flows into the right lower chamber, which pumps it to the lungs to pick up oxygen. Your blood then flows back into the upper chamber on the left-hand side of your heart, then into the left lower chamber. There it is pumped to the rest of your body to deliver oxygen. There are valves between the upper and lower chambers to make sure blood flows in the right direction.

1.3. What causes heart disease? Heart attacks are not normally caused by an infection. Your genes, your lifestyle, or most likely a mixture of both, all affect whether you suffer a heart attack. There isn’t one cause of heart attacks – there are many different risk factors. Your own risk of heart disease increases the more of these risk factors you are exposed to.

2. Making Vaccines Safe

2.1. Scientists go to the great lengths to make sure that vaccines are safe as they can be. Whenever creating a new cure or drug, it will need to be tested to see if there are any side effects. These are effects that are not wanted and may be harmful or unpleasant. Some individuals will have more side effects from prescription drugs than others, due to genetic variation.

3. Vaccines

3.1. The immune system is one of the ways that the body defends itself from diseases. One of the parts of the immune system is the white blood cells that make anti bodies to the proteins on the surface of pathogens.

3.2. The immune system has memory cells which remember what type of antigen to make if the same pathogen attacks the body again. Vaccines contain a safe microorganism that causes a disease. Once the vaccine is in the body, the immune system attacks the vaccine and develops memory cells against the antigens it carries. These memory cells respond very quickly if they meet the real disease-causing pathogens.

3.3. Babies and children undergo a course of vaccinations in their first year and as they prepare to go to school. Vaccines usually contain a weak or non-living form of the pathogen to ensure the the vaccination itself does not make the patient ill. Some pathogens are very stable with antigens that do not change much from year to year. The vaccines against these pathogens can stay the same for a long period of time. Other pathogens such as the flu virus, change rapidly and new vaccines must be developed every year to make sure the body will recognise the altered antigens on the pathogen. A vaccination from the previous year would not protect someone from the new strain of flu that appeared the following winter.

4. Drug Trials

4.1. Blind trials In some trials the doctor is told which patients are being given the drug. This may be because they need to look very carefully for certain unwanted harmful effects. The patient still should not know. This method is called a blind trial.

4.2. Open-label trials In an open-label trial both the patient and the doctor know the treatment. This may be necessary if, for example, a physiotherapy treatment was being compared to a drug treatment, or if a new drug is given to all the patients in a trial. This happens when there is no other treatment and patients are so ill that doctors are sure they will not recover from the illness. The risk of possible harmful effects from the drug is outweighed by the possibility that it could extend their lifespan or be a cure. No one is given a placebo. It would be wrong not to offer the hope of the new drug to all the patients. Penicillin is one example where this happened.

4.3. Double-blind trials In a double-blind trial, the volunteers do not know which group they are in, and neither do the researchers, until the end of the trial. This removes the chance of bias and makes the results more reliable. But double-blind trials are more complex to set up.

5. Microorganisms

5.1. There are 3 Main Types of Microorganisms: Bacteria, Fungi & Virus. Bacteria and Viruses can reproduce rapidly in ideal conditions. In warm, moist environments with plenty of food, bacteria can reproduce every 20 minutes. Bacteria reproduce by a process called Binary Fission. Viruses cannot reproduce without a 'host' cell. They hijack the host's cell's own mechanism for making proteins and use it to replicate (make copies of themselves). When a virus takes over a host cell, it reproduces very rapidly.

5.1.1. microorganisms reproduce quickly in the human body

5.2. Viruses cause illness in a different way from bacteria. Once a virus enters a body cell, it takes over the cell and uses it to make copies of itself. These copies can then infect other cells. Sometimes there is so much virus in a cell that it explodes.

6. White blood cell

6.1. Our bodies have a range of ways to defend us against the invasion of pathogens. The first line of defence is external: our skin with its ability to heal itself, our saliva and our tears. These body fluids either wash away invading microorganisms or destroy them before they can do any damage.

6.2. If a pathogen gets past the external defences and into our bodies, then the internal system of defence, called the immune system, starts to work. The system attacks pathogens by using different types to white blood cells.

6.3. Some white blood cells ingulf and digest them. Whilst another type of white blood cell produces antibodies that recognise and destroy particular microorganisms. As soon as a microorganism is detected, the white blood cell releases antibodies which stick to the antigens on the bacteria. This causes a large amount of bacteria to clump together so the white blood cell can engulf and digest them easily.

6.4. If the immune system has encountered a particular pathogen before, it can respond very quickly to the threat. The immune system recognises pathogens that it has encountered because the antigens in the pathogen's cell membrane stay the same.

6.5. If an antigen is recognised, cells of the immune system called Memory Cells are able to rapidly produce large numbers of antibodies to the pathogen and disable or destroy it before it is able to take hold in the body.

7. Mutation And Resistance

7.1. The word antimicrobial refers to a group of chemicals that are effective in destroying microorganisms. There are many different types of antimicrobial, and not all of them are effective against all organisms. Antibiotics are effective against bacteria, antifungals against fungi and antivirals against viruses.

7.2. Antibiotics are effective against bacterial infection, but not against viruses. This means they are of no use against common viruses such as colds and flu, unless a bacterial infection develops. This is why doctors do not prescribe antibiotics for the flu. The drugs would have absolutely no effect.

7.3. Bacterial resistance to antibiotics is a particular problem that scientists are working hard to resolve. As the number of types of antibiotic used has increased, so the incidence of antibiotic resistance has risen. Scientists call this a correlation. Antibiotic resistance has led to some strains of bacteria that are extremely difficult to eradicate. An example of a bacterium like this is MRSA.

8. Homeostasis

8.1. Inside your cells thousands of chemical reactions are happening every second. These reactions are keeping you alive. But for your cells to work properly they need certain conditions. Keeping conditions inside your body the same is called homeostasis. Homeostasis is not easy – lots of things have to happen for your body to ‘stay the same’. Look at just a few of the changes happening every second. Your body works hard to: • keep the correct levels of water and salt • control the amounts of nutrients • get rid of toxic waste products, for example, carbon dioxide and urea.

8.2. How does an incubator work? Premature babies cannot control their temperature, so they are put in incubators. The incubator is an artificial control system. An incubator has a temperature sensor, a thermostat with a switch, and a heater. If the temperature in an incubator falls too low, the heater is switched on. The temperature goes up. When the temperature is high enough, the heater is switched off. This type of control is called negative feedback:

8.3. Controlling water balance The control system for water balance is a negative feedback system. • Receptors in the brain detect any changes in concentration in the blood plasma. • When the concentration is too high, it triggers the release of a hormone called ADH from the pituitary gland in the brain. When the concentration is low, no ADH is released. • The ADH travels in the blood to the kidneys. These are the effectors. ADH affects the amount of water that can be reabsorbed back into the blood. The more ADH, the more water is reabsorbed.