The Cardiac Cycle, Heart and Cardiovascular Diseases

Consists of contraction (systole) and relaxation (diastole) of the atria and ventricles which keeps the blood pumping round the body-the volume of the atria and ventricles change as the cycle goes on.The pressure also changes due to the change in volume.

Three stages are:

-Atriol systole- the atrio-ventricular valves are open and blood flows in from the vena cava, through the right atrium and into the right ventricle. Then contraction of the right atrium sends the last of the blood into the ventricle

-Ventricular systole- this is where the right ventricle contracts, the pressure in the right ventricle rises above the pressure in the right atrium so the atrio- ventricular valves shut. As the ventrical continues to contract and pressure continues to rise the semi-lunar valves open in the pulmonary artery the blood then flows into here.

-Ventricular diastole- The ventricles relax and the pressure falls so the semi-lunar valves close in the pulmonary artery. As the pressure falls even further than in the right atrium the atrio-ventricular valves open allowing blood to move in again.

Heart muscle= myocardium, it is myogenic which means it doesn't require any external nervous impulses to make it contract- self stimulating

Sinoatrial node (SAN) generates an impulse or is moderated by the Atrioventricular node (AVN).

This signal causes contraction of the atrium and travels through conducting fibres to AVN nodes where there is a slight delay. It is carried by conducting fibres (Purkinje fibres that stem off Bundle of His in the septum) to lower ventricles which contract.

The right side of the heart carries deoxygenated blood (vena cava from head and body, pulmonary artery to the lungs) and the left side carries oxygenated blood (aorta to the head and body, pulmonary vein from the lungs).

The wall of the left ventricle has thicker muscle as it has to pump blood around the whole body, than the right.

Atherosclerosis- Degenerative disease in areas of the artery walls which become damaged (endothelial cells).

Macrophages release growth factors, encouraging growth of fibrous tissue. Cholesterol builds up and then this will eventually form plaques and the artery wall loses its elasticity- known as the inflammatory response. The lumen narrows, restricting blood flow (increasing blood pressure). If the plaque rupture, blood clotting is triggered. Blood clots are known as coronary thrombosis.

The fatty deposit is called atheroma. Fibrous tissue and calcium salts build up around this turning it into a hardened plaque. As blood pressure increases this makes damage in the endothelial lining more likely so more plaques form. Sometimes it can lead to a bulge in the artery which weakens the wall. This is know as an aneurysm- internal bleed often in the brain or the aorta, especially the abdomen.

Ultimately, cardiovascular diseases are caused by high blood pressure but risk factors are:

• Diet- an increase of fat/cholesterol/LDLs in blood leads to plaque formation in arteries (saturated fat is the most contributory).
• Exercise- a lack of this increases risk due to weakened circulation.
• Weight/Obesity- Blood pressure tends to be higher which leads to more plaque formation. Also the heart has to work harder to circulate the blood through all the extra tissue.
• Age- The older you are the greater risk as you have less elasticity in arteries and they can narrow slightly.
• Smoking- This constricts blood vessels therefore increasing blood pressure and heart rate, oxygenation can be decreased and increased fibrinogen and platelets leading to more clotting.
• Stress- Increase in cortisol hormones in the blood which causes increase in atherosclerosis.
• Genetics- In some families and ethnic groups CVD is developped and some are predisposed for high cholesterol levels which can cause high blood pressure and therefore resulting in aneurysms.

Antihypertensives- These reduce blood pressure so the risk of CVD is substantially reduced and the risk of damage to organs such as the kidneys and eyes is less. However, there are risks including blood pressure becoming too low which may lead to falls and injuries. Another way the body can react to the drugs is through side-effects; coughs, swelling of ankles, impotence, fatigue and constipation. These aren't serious but cause discomfort in the patient and so they may stop taking them putting themselves at risk.

Plant Statins- These lower the level of cholesterol in your blood by blocking the enzyme in the liver that is responsible for the production and effectively LDL production. They can also improve the balance of LDLs to HDLs and reduced inflammation in the lining of the arteries. Both of theses functions reduce the risk of atherosclerosis. Some people may suffer muscle and joint aches, nausea, constipation and diarrhoea but two serious side-effects are the triggering of muscle inflammation that can be fatal and liver problems.

Anticoagulants- These drugs help prevent blood clotting too easily, especially after heart surgery or after suffering with thrombosis. Low levels of prothrombin interferes with blood clotting. The dose has to be monitored carefully and there is a risk of internal bleeding. Age and condition is considered when deciding whther prescription is suitable.

Platelet Inhibitory Drugs- Platelets are made less sticky, and so chance of blood clotting is reduced. Cheapest and most common is aspirin but clopidogrel is used as well. Risk of aspirin is irritation of the stomach lining causing bleeding which can become serious. Two drugs can be combined but there has been research that side-effects occur.