Sunday 2 May 2010

Describe the structure of the heart and explain the cardiac cycle.


The heart is made up of cardiac muscle. The left side of the heart that deals with pumping out oxygenated blood has thicker walls than the right side which deals with de-oxygenated blood.
It has four chambers called the 'right atrium'(RA),' right ventricle'(RV), 'left ventricle'(LV), and the 'left atrium'(LA).
The (RA) and the (RV) are connected by a valve called the'Tricuspid'valve. The (LA) and the (LV) are connected by the 'Bicuspid' valve also referred to as the 'Mitral' valve. The valves are present to prevent back-flow of blood.
The heart also has two arteries and two veins by which blood enters and exits the heart. These are the'Vena cava' the 'Aorta' the 'Pulmonary artery' and the 'Pulmonary vein'.
De-oxygenated blood enters the (RA) via the Vena cava where it is pumped down through the Tricuspid valve into the (RV). From here it is pumped up through another valve called the 'Pulmonary valve' and out towards the lungs in the Pulmonary artery.
Once the blood has been oxygenated by gaseous exchange n the capillaries around the lungs, it is transported back to the heart. It enters the heart through the Pulmonary vein into the (LA). It is then pumped through the Bicuspid valve, down into the (LV). From here it is pumped up through a valve called the 'Aortic valve' and is carried out of the heart via the Aorta to the cells in the body needing oxygen. When the oxygen from the blood has been used it transports back to the (RA) where the process begins again.
The pumping of the blood through the Heart and around the circulatory system is caused by the contraction (systol) and the relaxation (diastol) of the atrium and the ventricles which is stimulated by electrical impulses from a group of electrical cells within the wall of the (RA) called the 'Sino-Atrial (SA) node.

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