Heart - Revision Doc [06Nov'10]

8/7/2019 Heart - Revision Doc [06Nov'10]

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Heart The Heart is a muscular organ that lies in the thoracic cavity

behind the septum.

Operates continually and tirelessly throughout a life of anorganism.

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Structure of the Heart

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Structure of the Heart The Atrium has thin walls and its elastic and thus it stretches

as it collects blood. It pumps blood to the ventricles.

Ventricles has a much thicker muscular walls. It pumps

blood either to lungs or to the rest of the body.

Both Atria contracts together and both ventricles contract

together.

The left atrioventricular (bicuspid) values, is present in the

left side of the heart has two flaps of fibrous tissue.

The right atrioventricular (tricuspid) valves, present in theright side of the heart has three flaps.



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Structure of the Heart The aorta is connected to the left ventricle and carries

oxygenated blood to all parts of the body except the lungs

The venacava is connected to the right atrium and brings

deoxygenated blood back from the tissues of the body.

The Pulmonary artery carries blood from the right ventricles

to the lungs

The pulmonary vein carries blood from the left ventricles to

the rest of the body.



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Supplying the Heart MuscleThe heart muscle is supplied by its own blood vessels, called the

coronary arteries, which branch off the aorta shortly after it leaves

the heart. Blockage of these arteries, e.g. by a blood clot, leads to

myocardial infarction, also known as heart attack, this is because

an area of the heart muscle is kept away from something needed,

i.e. oxygen and so dies.



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The Cardiac Cycle Relaxation of the heart (diastole) - blood enters the atria

from the pulmonary artery and the vena cava. As the atria

fills the pressure in the atrioventricular valves are forced

open allowing the blood to pass into the ventricles. The

muscular walls of both atria and ventricles are relaxed at this

stage.

Contraction of the atria (atrial systole) The muscle of the

atrial walls contract, forcing the remaining blood that they

contain (around 20% of the total blood in the heart) into the

ventricles

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The Cardiac Cycle Contraction of the ventricles (ventricular systole) After a

short delay to allow the ventricles to fill with blood, their

walls contract simultaneously.

This increases blood pressure within them forcing shutting

the atrioventricular valves and preventing the back flow of

blood into the atria.

With the atrioventricular valves closed, the pressure rises

further, forcing opening the semi lunar valves and pushing

blood into the pulmonary artery and aorta.



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Cardiac output Is the volume of blood pumped by one ventricle of the heart

in one minute. It is usually measured in dmmin and

depends upon two factors:

The heart rate (the rate at which the heart beats)

The stroke volume (volume of blood pumped out at each

beat)

Cardiac Output = heart rate x stroke volume



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Control of Heart Beat Mynogenic is also known as the cardiac muscle, i.e. its

contraction is initiated from within the muscle itself, rather

than by nervous impulses from outside (neurogenic), as in the

case of other muscles.

Within the walls of the right atrium of the heart is a distinct

group of cells known as the sinoatrial node (SAN). It is from

here that the initial stimulus for contraction originates. Has a

basic rhythm of stimulation that determines the beat of the

heart aka pacemaker.


Heart - Revision Doc [06Nov'10]

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