Definition of antigen and antibody.

An antigen is a 'marker' on a cell that is foreign to the body that identifies it as non-self.

An antibody is a protein produced by the body to destroy pathogens.

Phagocytosis and the role of lysosomes and lysosomal enzymes in the subsequent destruction of ingested pathogens.

Phagocytes are white blood cells. They destroy bacteria by engulfing them and breaking them down- this process is called phagocytosis.

The phagocyte recognises a pathogen because of its chemical products and so moves towards it.

It then binds with the pathogen and begins to engulf (wrap around) it- by doing this it forms a vesicle (sac) with the phagocyte inside it know as a phagosome.

Lysosomes (vesicles with enzymes inside) release digestive enzymes into the phagosome, this means that it can be broken down. Useful products are absorbed by the cell and others are excreted.

Risk factors associated with coronary heart disease: diet, blood cholesterol, cigarette smoking and high blood pressure. Candidates should be able to describe and explain data relating to the relationship between specific risk factors and the incidence of coronary heart disease

A number of factors can increase the risk of coronary heart disease:

Diet

• Salt raises blood pressure.
• Saturated fat increases blood cholesterol.

Blood cholesterol

• Low-density lipoproteins associate with white blood cells to cause atheromas.
• High-density lipoproteins help lower cholesterol.

Smoking

• Nicotine stimulates the production of adrenalin, this causes a quicker heart rate and therefore raises the blood pressure.
• Nicotine makes platelets stick together, so thrombosis is more likely.
• Carbon monoxide combines with heamaglobin so less oxygen can be carried in the blood. The heart has to pump more quickly to deliver the same amount of oxygen, so blood pressure is raised. The heart muscles may not get enough oxygen leading to a heart attack or angina (chest pain).

High blood pressure

• Arteries are put under more pressure so will form hard walls to resist the pressure- these thicker walls constrict blood flow.
• The pressure can burst open the arteries (haemorrhage).

Atheroma as the presence of fatty material within the walls of arteries. The link between atheroma and the increased risk of aneurysm and thrombosis. Myocardial infarction and its cause in terms of an interruption to the blood flow to heart muscle.

Atheroma is the name given to fatty build ups in artery walls: consisting of cholesterol, fibres, dead cells and white blood cells attached to fats.

Aneurysm
This is when an atheroma weakens an artery wall and it swells with blood making an aneurysm. If it bursts (haemorrhage) blood is lost- this can be fatal. In the brain this is what we know as a stroke.

Thrombosis
When an atheroma bursts the lining of an artery (endothelium) and obstructs blood flow. A clot (thrombus) can form here and block the vessel, or be carried around the body and block another vessel. The blocked off area doesn't receive oxygen so will die.

Myocardial infraction
This is a heart attack. A blockage stops blood getting to the heart tissue; the tissue doesn't receive enough oxygen and so gets damaged. The damage prevents the heart from pumping properly.

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The effects of fibrosis, asthma and emphysema on lung function.

Fibrosis
Scars in the lung tissue thicken the alveoli increasing the diffusion distance, decrease the volume in the lungs and reduce elasticity. This means that less air can be taken in, and oxygen diffuses more slowly decreasing the bodies supply.

• Shortness of breath- attempt to increase oxygen supply
• Cough- reflex to obstruction of the scars
• Pain- increased pressure
• Fatigue- lack of oxygen for respiration so less ATP (energy) is produced

Asthma

An allergic reaction causes white blood cells to release histamine, a chemical which inflames breathing pathways and constricts them (by contracting muscles)  and increases mucus.

• Difficulty breathing- constriction, inflammation and mucus
• Wheezing- constriction
• Tight feeling- lungs can't ventilate because of airway constriction
• Coughing- reflex to obstruction

Emphysema

Elastic tissue in the lungs looses its elastic properties due to smoking. The lungs can't recoil to push air out effectively, and so old air is not replenished and there is a reduced diffusion gradient. Alveoli break down so surface area and the walls thicken so the diffusion distance is increased. Due to these factors less oxygen can diffuse into the blood.

• Shortness of breath- attempt to increase oxygen supply
• Cough- reflex to obstruction of damaged tissue
• Blueish skin- low oxygen levels in the blood

The course of infection, symptoms and transmission of pulmonary tuberculosis.

Transmission

Mycobacterium tuberculosis and Mycobacterium bovis are bacteria that causes tuberculosis; it transmitted in aerosol (air born droplets) so can be transmitted by coughing, sneezing and spitting- providing some cells are breathed in. It can also be contracted from cows milk.

Risk of infection is increased by:

• Over crowded conditions
• Weak immune system
• Repeated contact with infect people

Course of infection

Primary infection:

• Bacteria enter the lungs and begin to multiply
• White blood cells go to attack them (engulfed by phagocytes) (encased in tubercle by macrophages)
• This inflames lymph nodes so they can't drain the lungs (causing cough)
• Often at this stage most bacteria are destroyed, but some may remain (dormant)

Post-primary infection:

• Years later the remaining bacteria cause a second infection (if immunosuppressed)
• They attack the epithelial cells- causing the infected person to cough it up damaged lung tissue
• The damage allows bacteria to enter the blood and spread to other organs
• The damage decreases the available surface area for gas exchange and makes the diffusion distance further, meaning sufferers will have reduced gas exchange

Symptoms

• Cough
• Fever
• Fatigue

In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, introns within genes and multiple repeats between genes.

Introns are sections of DNA that do not code for anything.

Sometimes they are in the middle of genes and sometimes they come between different genes.

Due to these introns very little of DNA has a code that actually makes proteins.