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What is the heart
The heart is a muscular organ found in all vertebrates that is
responsible for pumping blood throughout the blood vessels by
repeated, rhythmic contractions.
It is divided into 4 chambers; the right atrium, the left atrium, the
right ventricle and the left ventricle. The ventricles and atria are
separated by a wall of muscle called the septum
One-way valves between the chambers keep blood flowing
through your heart in the right direction. As blood flows through
a valve from one chamber into another the valve closes,
preventing blood flowing backwards. These are attached to
tendinous cords which attach to the ventricles which prevent the
valves from turning inside out thus allow backwards blood flow…read more

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What is the heart continued
Your heart is a single organ, but it acts as a double pump. The
first pump carries oxygen-poor blood to your lungs, where it
unloads carbon dioxide and picks up oxygen. It then delivers
oxygen-rich blood back to your heart. The second pump delivers
oxygen-rich blood to every part of your body.
The coronary arteries lie upon the surface of the heart. They feed
the organ with much needed oxygenated blood. If these become
blocked they may cause angina or a heart attack
Your right ventricle pumps blood to your lungs and your left
ventricle pumps blood all around your body. The muscular walls
of the left ventricle are thicker than those of the right ventricle,
making it a much more powerful pump. For this reason, it is
easiest to feel your heart beating on the left side of your chest.…read more

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What is the heart continued
The heart is made of cardiac muscle, composed of cells
called myocytes. When myocytes receive an electrical
impulse they contract together, causing a heartbeat.
Since myocytes are constantly active, they have a great
requirement for oxygen, so are fed by numerous
capillaries from two coronary arteries.
Cardiac muscle is myogenic, which means that it can
contract on its own, without needing nerve impulses.
Contractions are initiated within the heart by the sino-
atrial node (SAN, or pacemaker) in the right atrium.
This extraordinary tissue acts as a clock, and contracts
spontaneously and rhythmically about once a second,
even when surgically removed from the heart.…read more

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The cardiac cycle has three stages:…read more

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