Anatomy
Fist-sized blood- pumping muscular (involuntary striated) organ, left of centre in thorax. A double pump with separating septum, each part/side (right and left) comprising 2 chambers – an atrium (into which a vein delivers blood) and a ventricle (from which blood is pumped to an artery) and 2 valves (cuspid between atrium and ventricle, semilunar between ventricle and artery). Circulatory pathway; superior/inferior venae cava – right atrium – tricuspid valve – right ventricle – pulmonary valve – pulmonary artery – lungs – pulmonary vein – left atrium – mitral (bicuspid) valve – left ventricle – aortic valve – aorta – periphery – venae cava. Heart musculature supplied by right and left coronary arteries.
Clinical
Cardiac electrical conduction system delivers co- ordinated, staggered, efficient cycle of atrial and ventricular contraction (systole) and relaxation (diastole) and hence efficient blood circulation. Pathway; sinoatrial (SA) node (high wall right atrium) – internodal pathways, Bachmann’s bundle – atrioventricular (AV) node (lower part interatrial septum) – bundle of His, bundle branches, purkinje fibres (down to apex and coursing back up ventricles).
There is an intrinsic rhythm and particular responsiveness to autonomic nervous system. Right heart receives high-CO2, O2-depleted blood from systemic veins, pumps it through pulmonary arteries to lungs. Left heart receives O2- replenished blood from pulmonary veins, pumps it back through systemic arteries to periphery.
Vignette
High (systemic) blood pressure (hypertension) common; heart has to work harder, gets thicker, expands, can eventually decompensate. Coronary artery disease (CAD) common; vessels narrowed by atherosclerosis (genes, eating, exercise, smoking), eventually compromising oxygenation of cardiac musculature (angina/cramp or blockage/infarction).
Cardiomyopathy; disease of muscle itself; causes include hypertension, CAD, alcohol, faulty valves). At rest, heart pumps c. 5.5L (male), 5L (female) in 1 minute.
Taking heart rate of 70/min, over 70 years, total volume pumped; 200/185,000,000 litres (male/female); equivalent to volume of water in 8 olympic swimming pools (50 X 25 X 1 metres).
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