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The Heart
Humans have a double circulatory system with a 4-chambered heart.

The heart is a muscular pump.

It has a left pump and a right pump:

Pump Function
Left Deals with oxygenated blood
Pumps blood to the rest of the body
Systematic circulation

Right Deals with deoxygenated blood

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Between each atrium and ventricles are valves that prevent the backflow of blood into the
atria when the ventricles contract.

There are two sets of valves:

Valve Properties and Function
Left Atrioventricular Valves Two valves
Formed of two cup-shaped flaps on the left
side of the heart

Right Atrioventricular…

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Each of the four chambers of the heart is served by large blood vessels that carry blood
towards or away from the heart.

The ventricles pump blood away from the heart and into the arteries.

The atria receive blood from the veins.

Vessels connected to the four chambers are therefore…

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The Cardiac Cycle

The heart undergoes a sequence of events that is repeated about 70 times per minute.

This is known as the cardiac cycle.

There are two phases to the beating of the heart:

Contraction - systole
Relaxation ­ diastole

Cardiac muscle is myogenic which means that it can…

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Contraction of the Atria ­ Atrial Systole
The muscle of the atrial wall contracts, forcing the remaining blood that they contain into
the ventricles.

The blood only has to be pushed a very short distance and
therefore the muscular walls of the atria are very thin.

During this stage, the…

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Valves in the Control of Blood Flow
It is important to keep blood flowing in the right direction through the heart around the
body. This is achieved mainly by the pressure created by the heart muscle.

Blood, as with all liquids and gases, will always move from a region of…

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Cardiac Output

Cardiac output is the volume of blood by one ventricle of the heart per minute.

It is usually measured in dm³ min -1.

It depends upon:

Heart rate
Stroke volume

Cardiac Output = heart rate x stroke volume

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Controlling the Cardiac Cycle
Cardiac muscle is myogenic ­ its contraction is initiated from within the muscle itself, rather
than by the nervous impulses from outside.

Within the wall of the right atrium of the heart is a distinct group of cells known as the
sinoatrial node.

It is from…

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Heart Disease
Coronary heart disease affects the pair of blood vessels, the coronary arteries which supply
the heart muscle with the glucose and oxygen that it requires for respiration.

Blood flow through these vessels may be impaired by the build-up of fatty deposits known
as atheroma.

If blood flow to…

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If an atheroma breaks through the lining of the blood vessel, it forms a rough surface that
interrupts the otherwise smooth flow of blood.

This may result in the formation of a blood clot, or thrombus, in a condition known as

This thrombus may block the blood vessel,…


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