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The heart as a pump
The heart is a specialised organ which pumps blood to the body. It consists of muscle, electrical tissue, valves and vessels.  It has four chambers. The two collecting chambers, or ‘atria’, collect ‘blue’ (deoxygenated) blood from the veins and deliver it to the pumping chambers, or ‘ventricles’. The right ventricle pumps ‘blue’ blood to the lungs, where the blood becomes bright red after taking up oxygen. This 'red’ (oxygenated) blood, returns to the left atrium, which delivers it to the left ventricle. The left ventricle in turn pumps oxygenated blood to the rest of the body. In this way the heart constantly drains the lungs of blood and pumps it to the rest of the body. This includes the heart itself, through the coronary arteries.
The heart valves

The normal heart cycle (one pulse) starts with contraction of the upper chambers (atria), which deliver blood to the main pumping chambers (ventricles). There are four valves:

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  • Aortic valve: connects the left ventricle to the aorta

  • Mitral valve: connects the left atrium to the left ventricle

  • Tricuspid valve: connects the right atrium to the right ventricle

  • Pulmonary valve: connects the right ventricle to the pulmonary artery

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The function of the heart valves is to contain blood within each chamber within the cardiac cycle and to let it through at he right time. When the heart valves are damaged, blood flows in abnormal directions. This creates an imbalance of pressure within the heart which can ultimately lead to heart failure.

Video: the heart as a pump
The electrical system of the heart

Video: the heart as a pump

The normal heart has its own pacemaker, which consists of specialised conducting tissue akin to nerves. The circuit consist of a small group of cells in the upper right chamber (right atrium) – the sinoatrial (SA) node. Impulses from this node are transmitted to the atrioventricular (AV) node, which is placed at the junction of the atria and ventricles. Transmission of impulses then go through to the ventricles via the so-called the Bundle of His and Purkinje network of specialised conducting tissue. These specialised fibres transmit impulses to the various muscles of the heart, which contract (systole) and relax (diastole).

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Disturbances in the generation and transmission of impulses through the conducting tissue of the heart leads to slow heart rhythms (bradycardias) or fast heart rhythms (tachycardias).

Heart links

http://en.wikipedia.org/wiki/Heart

http://en.wikipedia.org/wiki/Electrical_conduction_system_of_the_heart

 

For anatomy of the heart: http://www.blaufuss.org/tutorial/index1.html





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Video: heart valves

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