The cardiovascular system 1

Posted by DAM on February 10, 2012 in The cardiovascular system | Short Link
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The cardiovascular system 1

 

The cardiovascular system includes the heart and the blood vessels.

THE HEART: (Fig. 19)

      The heart is a hollow muscular organ present in the thoracic cavity between the two lungs. It is conical in shape. Its apex is located in the 5th left intercostal space (9 cm from the middle line) just below the left nipple.

      The heart consists of 4 chambers: two atria and two ventricles.

      On the external surface of the heart, the atria are separated from the ventricles by a groove known as the atrioventricular groove which lodges the coronary arteries that supply the heart Internally, the two atria are separated.

by the interatrial septum while the two ventricles are separated by the interventricular septum.

The heart could be divided into two halves which, are completely separate from each other. The right half consists of the right atrium and the right ventricle. The left half consists of the left atrium and left ventricle. The

right half of the heart contains deoxygenated (impure) blood while left half contains the oxygenated (pure) blood.

The right Mr’mm (Fig. 20) receives blood from the superior vena cava (which carries deoxygenated blood from the upper half of the body) and the inferior vena cave (which carries the deoxygenated blood from the lower half of the body).

It opens into the right ventricle by an opening guarded by a valve formed of three cusps known as the tricuspid valve which permits the flow of blood in one direction from the right atrium to the right ventricle.

The left atrium (Fig. 2r) receives the four pulmonary veins which carry the oxygenated (pure) blood from the lungs to the heart.

It opens into the left ventricle by an opening guarded by a

valve formed of two cusps, known as the mitral valve which permits the flow of blood in one direction from the left atrium to the left ventricle.

The right ventricle (Fig. 20) pumps the blood into the pulmonary trunk which communicates with the right ventricle by and opening (pulmonary opening) guarded by 3 semilunar cusps that allows the blood to flow in one

 

 

 

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direction from the right-ventricle to the pulmonary trunk which carries the impure blood to the lungs.

      The left ventricle (Fig. 20) pumps the blood into the ascending aorta through the aortic opening which is guarded by the aortic valve composed of 3 semilunar cusps. The valve permits the flow of pure blood in one direction from the left ventricle to the ascending aorta and then to all parts of the body.

      The wall of the atrium is thinner than that of the ventricle because the atrium pumps blood only to the ventricle while the wall of the ventricle is thicker because it pumps the blood to distant areas. Also the wall of the left ventricle is 3 times thicker than that of the right ventricle because it pumps blood to all parts of the body.

The internal aspect of the wall of both ventricles presents muscular processes called papillary muscles which are connected to the cusps of the atrioventricular valve (tricuspid or mitral valve) by chordae tendinae. The papillary muscles and the chordae tendinae prevent eversion of the cusps toward the atria during contraction of the ventricles.

 

The Blood Vessels:

The blood vessels include arteries, veins and capillaries.

a)     TSie arteries: carry the pure oxygenated blood from the heart to the different parts of the body (except the pulmonary artery which carries the impure deoxygenated blood from the heart to the lungs)

b) Tise veins: carry the impure deoxygenated blood from the different parts of the body to the heart (except the -34­pulmonary veins which carry the pure oxygenated blood from the lungs to the heart).

c) The blood capillaries: are very minute blood vessels located in the tissues at the terminal part of an artery and the beginning of a vein connecting them together.

Ttae differences between an artery and a vela

No. |

Artery

Vein

1

Carriers the blood from the heart to the tissues.

Carries blood from the tissues to the heart.

2

It transmits oxygenated blood (except the pulmonary artery).

It transmits deoxygenated blood (except the pulmonary veins).

3.

lis wall is thick as it contains a thick muscular laver

Its wall is thin.

4

Its wall contains an elastic layer so that it does not j collapse when cut.

Its wall does not contain an elastic layer so that it does collapse when cut.

5

It is not provided with valves

It is provided with valves

 

 

 

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