The Heart - AS Applied Science - Biology - Unit 2

Circulation in mammals is a double circulatory system . This means that the blood goes through the heart twice for each circuit of the body. 

Superior Vena CavaCarries deoxygenated blood from the body to the heartSemilunar ValveFlaps that prevent backflow of bloodLeft AtriumReceives oxygenated blood from the lungsLeft VentricleRegion of the heart that pumps blood to the bodyPulmonary ArteryCarries blood to the lungsRight VentricleRegion of the heart that pumps blood to the lungsPulmonary VeinCarries blood from the lungsRight AtriumSegment of the heart that receives deoxygenated bloodAortaThe main artery carrying blood to all parts of the body

Heart cycleDiastole - relaxation - blood flows from veins into the heartSystole - contraction - atria briefly contract, then the ventricles contract forcing blood outAtrial systole - both atria contract and push stored blood across AV valves into ventricles Ventricular systole - After atria contracts, ventricles begin to contract pressure in ventricles increases. Volume is reduced and blood is ejected into arteries through aortic and pulmonary valves.Ventricular diastole - End of cardiac cycle, all chambers relax. Atria begin to fill up again to start next cycle volume increases and pressure decreases; led to uncontentious and death

SA node = the pacemaker of the heart located in the right atriumAV node = transmits the nervous signal to the bottom of the ventricles and is located in the septum (between the two halves of heart at bottom)Bundle of His = these are muscle fibres that conduct electrical impulses which regulate the heartbeat. Purkinje fibres = this is one of the specialized cardiac muscle fibres, contributing to the network of the heart transmitting impulses from the atrioventricular to the ventricles. 

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