Parts and functioning of the heart

The heart

Blood returning via the vena cava enters the right atrium.  The resulting pressure in this chamber forces and opens the flaps of the tricuspid valve. The result is that blood flows through the atrioventricular opening into the right ventricle. When the atrium and ventricle are full of blood the atrium suddenly contracts, propelling the remaining blood into the ventricle.  The contraction spreads from the right atrium over the rest of the heart.  Atrial systole is relatively weak but the ventricles, whose thick walls are particularly well endowed with muscles, contract more powerfully.  As a result, blood is forced from the right ventricle into the pulmonary artery. The blood is prevented from flowing back into the atrium by the flaps of the atrioventricular opening.  The atrioventricular valve is prevented from turning inside out by tough strands of connective tissue, the tendinous cord or “heartstrings” which run from the underside of each flag to the wall of the ventricle Once in the pulmonary artery, blood is prevented from flowing back into the ventricle by pocket like semilunar valves guarding the opening of the pulmonary artery. From the lungs, oxygenated blood returns to the left atrium via the pulmonary veins.  It is then conveyed to the left ventricle and so into the systemic arch which leads to the aorta.  The flow of blood takes place in the atrioventricular valve consists of two flaps rather than three, for which reason.  It is called the bicuspid valve.  It is also known as the mitral valve because its two flaps are rather like a bishop’s miter. Although systole starts at the right atrium, it quickly spreads to the left so that the whole heart appears to contract synchronously.  The de-oxygenated blood is pumped from the right ventricle into the pulmonary artery at the same time as oxygenated blood is pumped from the left ventricle in the aortic arch. Systole is followed by diastole during which the heart refills with blood again. The entire sequence of events is known as the cardiac cycle. Please find free downloadable notes, exams and marking guides of agriculture, biology, Physics, chemistry etc.  from digitalteachers.co.ug website. Dr. Bbosa Science