Cardiovascular Disease

 
 

Atheroma formation

Atherosclerosis a process in which the artery lining becomes hard due to the build-up of fatty material in the artery wall. It is a problem because it can lead to the artery becoming completely blocked, cutting off blood circulation and leading to events like a heart attack or stroke. It occurs in the following stages:

  • The inner lining of the artery wall (the endothelium) becomes damaged due to high blood pressure (hypertension).

  • This triggers an inflammatory response - white blood cells (such as macrophages) move towards the site of damage and accumulate with lipids (fats) which are circulating in the blood. The accumulation of these substances underneath the artery wall leads to the formation of fatty streaks in the endothelium.

  • The fatty streaks develop into an atheroma, causing the lumen of the artery to become narrower and restricting blood flow. This causes blood pressure to increase further.

  • The hardening of arteries, caused by the development of atheromas, is referred to as atherosclerosis.

 

Cardiovascular disease

The formation of an atheroma in an artery causes partial blockage of an artery. If the atheroma ruptures, it can trigger a blood clot to form which may completely prevent blood flow. The stages of this process occur as follows:

  • The atheroma ruptures and bursts through the endothelium of the artery, damaging the artery wall.

  • This triggers blood clotting (thrombosis) at the site of damage.

  • The blood clot can cause a complete blockage within the artery.

  • This prevents blood flow in the artery which means that oxygen isn’t delivered to the tissues downstream of the artery.

  • The cells within the tissue cannot carry out aerobic respiration and will start to die.

If the blockage happens within a coronary artery, the blockage will lead to a heart attack. If it occurs in a blood vessel leading to the brain it will cause a stroke and if it happens in an artery in the legs in can cause deep vein thrombosis (DVT).

 
 
 

Blood Clotting

Fragments in our blood, called platelets, clump together at the site of a wound to prevent the excessive loss of blood when we injure ourselves. It also prevents microorganisms from entering our body when the skin’s protective barrier is broken. However, when this process happens inside arteries it can be dangerous as it has the potential to completely restrict blood flow within the vessel.

The process of blood clotting (thrombosis) takes place in the following stages:

  • An enzyme called thromboplastin is released from damaged blood vessels. It requires calcium ions in order to function.

  • Thromboplastin catalyses the formation of prothrombin into thrombin, which is itself an enzyme.

  • Thrombin catalyses the formation of fibrinogen into fibrin. Fibrinogen is a soluble protein that is dissolved in the blood. Fibrin is insoluble and forms fibres which tangle together platelets and red blood cells to form a blood clot. 

 

Risk factors for CVD - Lifestyle factors

Things which increase our risk of developing cardiovascular disease can be grouped into lifestyle factors (things which result from our behaviour and are under our control) and non-lifestyle factors (things that we were born with and cannot control). Some of these factors are interlinked - for example, the genes you have may mean that you are more susceptible to high blood pressure, which is also affected by your diet.

Smoking

  • The nicotine in cigarette smoke makes platelets stickier, increasing the chance of a blood clot forming which could lead to blockage in the arteries.

  • Carbon monoxide in cigarette smoke binds to haemoglobin in red blood cells, reducing the amount of oxygen being transported in the blood. This means the heart has to pump faster to get the same amount of oxygen delivery, which increases blood pressure.

  • Smoking also reduces levels of antioxidants in the blood. Antioxidants are molecules in our body which can protect the arteries from damage. The reduced levels of antioxidants in smokers can increase the likelihood of endothelial damage and atheroma formation.

High blood pressure

  • High blood pressure puts more strain on the artery walls and means they are more likely to suffer damage. This leads to the process of atherosclerosis which in turn can lead to blood clotting and cardiovascular disease.

  • A diet high in salt, high alcohol consumption, inactivity and stress can increase blood pressure.

Diet

  • A diet high in saturated fats and low in unsaturated fats can increase the risk of CVD. Consumption of saturated fats increases blood cholesterol levels which increase the likelihood of atheroma formation.

  • A diet high in salt can increase the risk of CVD by increasing blood pressure.

Lack of exercise

  • A sedentary lifestyle can increase the chances of CVD by increasing blood pressure.

Risk factors for CVD - Non-lifestyle factors

Age

  • The risk of CVD increases with age (heart attacks are much more uncommon in people under the age of 40).

  • This is because the fatty deposits which accumulate in our arteries build up over time.

Genetics

  • Some people possess alleles which increase cholesterol production or make them more susceptible to high blood pressure.

  • Likewise, other people can inherit beneficial alleles which will reduce their risk of CVD by dampening down cholesterol production or giving them slightly lower blood pressure.

Gender

  • Men are at a much greater risk of developing CVD than women due to lower oestrogen levels.

  • Oestrogen increases the levels of ‘good’ cholesterol (HDLs) which removes the amount of cholesterol circulating in the blood. This reduces the risk of atheroma formation.

 

Treatments for CVD

Antihypertensives - beta-blockers and vasodilators are two types of drug which act as antihypertensives since they work by lowering blood pressure. A lower blood pressure means there is a lower risk of endothelial dysfunction (damage to the artery wall). The side-effects of antihypertensives include heart palpitations, fainting, headaches and drowsiness.

Statins - these are drugs which work by reducing cholesterol levels by lowering the LDL concentration in the blood. Side-effects of statins include muscle pain, nausea, headaches, increased risk of diabetes and problems with the digestive system.

Anticoagulants - these are substances which reduce blood clotting. The risks include excessive bleeding if the person injures themselves, allergic reactions, tissue swelling and osteoporosis.

Platelet inhibitors - these are also substances which reduce blood clotting which work by preventing platelets from sticking together. The side-effects include rashes, nausea, liver dysfunction, diarrhoea and excessive bleeding if an injury occurs.