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Heart and Heart Disease Summary
The heart has two sides, left and right, which both comprise of an atrium and ventricle. The
left side pumps to the whole body, therefore is larger. The right side pumps to the lungs,
therefore is smaller.
There are four blood vessels connected to the heart:
Vena cava Connected to the right atrium and carries
deoxygenated blood from the body.
Pulmonary artery Connected to the right ventricle and carries
deoxygenated blood to the lungs.
Aorta Connected to the left ventricle and carries
oxygenated blood to the body.
Pulmonary vein Connected to the left atrium and carries
oxygenated blood from the lungs.
Remember `AV' vena cava and pulmonary artery; and aorta and pulmonary vein.
The muscle surrounding the ventricle walls is much thicker than the atria, as they are pumping
blood much further (around the whole body).
The blood must pass through the heart twice in one circulation, as pressure levels would drop
otherwise and blood would not be able to pass through capillaries back to the heart.
The cardiac cycle consists of 3 stages.
1. Diastole is the relaxation of both atria and ventricles, allowing them to fill with blood.
2. Atrial systole is the contraction of the atria, forcing blood into the ventricles.
3. Ventricular systole is the contraction of the ventricles, pushing blood into either the
aorta or pulmonary artery.
Diastole Atrial systole Ventricular systole
Atria Relaxed Contracting Relaxed
Ventricles Relaxed Relaxed Contracting
Atrioventricular Open Open Closed
Semi-lunar valves Closed Closed Open
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Changes in blood pressure cause the opening and closing of valves (AV, semi-lunar and
pocket). For example, in ventricular systole, the AV valves are closed, as blood pressure is
higher in the ventricles than atria.
The heart is myogenic, and the cardiac cycle is controlled by electrical impulses within the
It occurs in the following way:
1. A wave of electrical activity is released from the sinoatrial node (SAN), which
spreads down the atria.
2. The atria contract.…read more
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The weakened section then swells, causing a balloon shape. This area often bursts, causing a
haemorrage. Blood can no longer reach the area.
When aneurysms occur in the brain, it is called a cerebrovascular accident (CVA), or a stroke.
The main factors that increase the risk of heart disease are:
Smoking. Carbon monoxide decreases the oxygen-carrying capacity of the blood,
meaning the heart must work harder. Nicotine stimulates the production of
adrenaline, raising blood pressure.
High blood pressure.…read more