AS Biology Chapter 1.2 The Heart and Health

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Chapter 1.2 ­ The heart and health
The inferior vena cava As the right atrium fills up with The tricuspid valve is also
collects blood from the blood, the pressure builds up and known as an atrioventricular
lower parts of the body, opens the tricuspid valve, so the valve as it separates an atrium
which is low in oxygen right ventricle starts to fill with and ventricle. The valve allows
and high in CO. The blood too. When the atrium is full blood to pass from the atrium
superior vena cava it contracts forcing blood into the into the ventricle but not the
receives blood from the ventricle. The atrium is made with other way around. The
upper parts of the body. thin muscular walls because it tendinous cords make sure
This blood is delivered to receives blood at low pressure that the valves are not turned
the right atrium. and exerts little pressure to move inside out by the great
the blood into the ventricle. pressure exerted when the
ventricles contract.
As the left atrium contracts
The blood returns from the The right ventricle is filled
the left ventricle is filled with
lungs to the left side of the heart with blood under some
blood under high pressure.
in the pulmonary veins. The pressure when the atrium
The left ventricle then
blood is at a low pressure after contracts. Its muscular walls
contracts forcing blood out
passing through the extensive produce the pressure
of the heart and into the
capillaries in the lungs. The needed to force blood out of
aorta. The left side has more
blood returns to the left atrium. the heart and into the
thicker muscular walls
It contracts to force blood into pulmonary arteries. This
because it needs to pump
the left ventricle. Backflow is carries the deoxygenated
blood around the body.
prevented by the bicuspid blood to the lungs.
A heartbeat is a sound produced when the blood is forced against the atrioventricular valves when
the ventricles contract and when the blood hits the semilunar valves in the pulmonary artery and
aorta as the ventricles relax. The rate of your heartbeat shows how fast your heart is contracting. It
makes a `lub dub' sound.
Cardiac Cycle ­ When the heart contracts it's called systole. Systole is divided into atrial systole,
when the atria contract together forcing blood into the ventricles and ventricular systole, when the
ventricles contract forcing blood into the pulmonary artery and the aorta. Between contractions, the
heart relaxes and the atria fill with blood. This relaxation stage is called diastole. One cycle of systole
and diastole make up a single heartbeat, which lasts about 0.8 seconds in humans.
The heart rate is increases by exercise, stress or excitement, whilst rest and relaxation lower it.
Intrinsic Rhythmicity ­ When the heart beats rhythmically. The intrinsic rhythm of the heart is
maintained by a wave of electrical excitation, similar to a nerve impulse, which spreads through
special tissue in the heart muscle. The heart has its own basic rhythm so the body's resources are
not wasted on maintaining this continuous activity.
Receptors in the blood vessels respond to changes in the CO levels. They send signals to the
cardiovascular centre in the brain. This sends signals to the brain.

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When the heart contracts the blood pressure in the arteries is at its highest. When the heart relaxes,
the blood pressure in the arteries falls.
The friction between the blood and the vessel walls is called peripheral resistance. It slows down the
flow of blood.
Little pressure is lost when the blood goes through the arteries because they are wide so offer little
resistance to the flow.…read more

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The lumen of the artery gets smaller because if the plaque. This increases the blood pressure making
it hard to pump blood around the body. This raised blood pressure makes damage more likely in the
endothelial lining, so more plaques form, which further increases the blood pressure.
Aneurysm ­ When an artery is narrowed by plaque, the blood builds up behind the blockage. The
artery bulges up and is under a lot more pressure, causing the wall of the artery to be severely
weakened.…read more


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