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Monday, July 4, 2011

Biology- The structure of the Heart

The first diagram is a cut-away section through the heart, showing its physical appearance and labelling its major components and blood vessels. The simpler diagrams below it are line drawings including essential information in a form that is easier to reproduce in exams.

Illustration of the Physical Form of the Heart

The heart is a muscular cone-shaped organ about the size of a clenched fist of the same person.
It is located in the upper body (chest area) between the lungs, and with its pointed end (called the apex) downwards, forwards, and pointing towards the left. The main purpose of the heart is to pump blood around the body.

The basic structure of the heart (illustrated above) may be described as follows:
The Heart is divided into separate right and left sections by theinterventricular septum, or "septum" when the context is clearly that of the heart. Each of these (right and left) sections is also divided into upper and lower compartments known as atriaand ventricles, respectively.
The four main chambres of the heart are therefore the:
Right Atrium (Labelled "RA" in the diagrams on this page);
Right Ventricle (Labelled "RV" in the diagrams on this page);
Left Atrium (Labelled "LA" in the diagrams on this page);
Left Ventricle (Labelled "LV" in the diagrams on this page).

Deoxygenated blood (from the body) is pumped through the right atrium and the right ventricle (to the lungs), while oxygenated blood (from the lungs) is pumped through the left atrium and the left ventricle (to the body).
Deoxygenated blood enters the right atrium from the Superior vena cava and the Inferior vena cava.
Deoxygenated blood leaves the right ventricle by Pulmonary artery, which takes blood to the lungs via the right and left brances of the pulmonary artery.
Oxygenated blood enters the left atrium from the Pulmonary veins. These may be labelled as "right pulmonary veins" and "left pulmonary veins".
Oxygenated blood leaves the left ventricle by Ascending aorta, which takes blood to the body via its system of arteries, arterioles, and capillaries. Major arteries leading from the heart (via the ascending aorta) include thebrachiocephalic artery, the left common carotid artery, and the left subclavian artery (illustrated above). These are just a few of the main arteries of the body.

It is essential that blood flows in the correct direction through the heart so the structure of the heart includes a series of valves.
The Tricuspid valve separates the right atrium from the right ventricle.
The Pulmonic / Pulmonary valve separates the right ventricle from the pulmonary artery.
The Mitral (also known as the Bicuspid) valve separates the left atrium from the left ventricle.
The Aortic valve separates the right ventricle from the ascending aorta.

Another Short Explanation
Blood flows through the heart in one direction, from the atria to the ventricles, and out of the great arteries, or the aorta for example. Blood is prevented from flowing backwards by the tricuspid, bicuspid, aortic, and pulmonary valve.

The heart acts as a double pump. The function of the right side of the heart (see right heart) is to collect de-oxygenated blood, in the right atrium, from the body (via superior and inferior vena cavae) and pump it, via the right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the passive process of diffusion.

The left side (see left heart) collects oxygenated blood from the lungs into the left atrium. From the left atrium the blood moves to the left ventricle which pumps it out to the body (via the aorta).

On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systemic circulation.

Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here, it is pumped out of the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, blood flows back through the pulmonary vein to the left atrium. It then travels through the mitral valve to the left ventricle, from where it is pumped through the aortic semilunar valve to the aorta and to the rest of the body. The (relatively) deoxygenated blood finally returns to the heart through the inferior vena cava and superior vena cava, and enters the right atrium where the process began.

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