The Heart and Heart Disease

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  • Created on: 25-01-15 19:30
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The Heart
Structure and function
Mammals have a double circulation; a pulmonary circulation and a systemic circulation.
The pulmonary circulation takes blood on the relatively short journey to the lungs, where blood is
oxygenated. When blood passes through a system of capillaries it loses pressure, so it must return
to the heart for a pressure boost before it enters the systemic circulation, which takes blood
around the rest of the body.
The mammalian heart has four chambers, two atria and two ventricles. All chambers have
approximately the same volume, so with each heartbeat an equal volume of blood passes to the
lungs and to the whole of the rest of the body. Atrioventricular (AV) valves prevent backflow of
blood from ventricles to atria. Semi-lunar valves prevent backflow of blood from arteries to
ventricles.
Each heartbeat is known as a cardiac cyle, which can be divided into three stages:
1. Both atria contract, forcing the blood into the venticles­ atrial systole
2. Both ventricles contract, increasing the blood pressure and forcing shut the AV valves. The
increase in pressure forces open the semi-lunar valves, pushing blood into the pulmonary
artery and aorta ­ ventricular systole
3. All chambers relax. Lower pressure in the ventricles than arteries means semi-lunar valves
shut­ diastole

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Cardiac output is the volume of blood pumped by one ventricle of the heart in one minute.
Cardiac output = heart rate x stroke volume
Cardiac muscle is myogenic (contraction is initiated from within the muscle itself rather than by
nervous impulses from outside, as is the case with other muscles). Within the wall of the right
atrium of the heart there is a group of cells known as the sinoatrial node (SAN). It is from here that
the initial stimulus for contraction initiates.…read more

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The biological basis of heart disease
Cardiovascular disease is the biggest single cause of death in the UK. The common underlying
cause of cardiovascular disease is the build up of an atheroma in the walls of arteries.
An atheroma begins as fatty streaks that are accumulations of white blood cells that have taken up
LDLs. These streaks enlarge to form atheromatous plaques which most commonly occur in larger
arteries and are made up of deposits of cholersterol, fibres and dead muscle cells.…read more

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Arteriosclerosis ­ loss of elasticity and hardening of the arteries making them more liable to
rupture.
Atherosclerosis ­ a build up of atheroma in the blood vessels.
Risk factors
Smoking:
Giving up smoking is the single most effective way of increasing life expectancy. There are two
main constituents of tobacco smoke that increase the likelihood of heart disease.
Carbon monoxide ­ combines irreversibly with haemoglobin in red blood cells to form
carboxyhaemoglobin, thereby reducing the oxygen-carrying capacity of the blood.…read more

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High intake of saturated fats ­ increase in LDL levels and hence blood cholesterol
concentration.
By contrast dietary fibre and antioxidants reduce the risk of heart disease.…read more

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