Cardiac circulation, valve movements and the Windkessel effect
THE CONTEXT
Blood passes through the pulmonary and systemic circulations through coordinated cardiac filling and ejection. Elastic central arteries help sustain pressure and flow between contractions.
Path of blood through the heart
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The right atrium receives deoxygenated blood from the superior and inferior venae cavae and delivers it to the right ventricle, which pumps it into the pulmonary artery.
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Blood becomes oxygenated in the pulmonary alveolar capillary bed, then returns through the pulmonary veins to the left atrium.
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Blood passes from the left atrium into the left ventricle, which ejects it into the aorta.
Valve movements during the cardiac cycle
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During ventricular systole, the tricuspid and mitral valves close while the pulmonary and aortic valves open.
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During diastole, the pulmonary and aortic valves close while the two atrioventricular valves open.
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The coordinated atrial and ventricular events constitute the cardiac cycle of filling and ejection from one heartbeat to the next.
Systemic vessels and arterial recoil
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Blood travels through large central elastic arteries, muscular arteries and resistance vessels called arterioles before reaching capillaries, where nutrients, oxygen and metabolic waste products are exchanged.
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Central arteries such as the aorta consist predominantly of elastic tissue, with little or no vascular smooth muscle.
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The compliant aorta expands during ejection. Its elastic recoil sustains blood pressure and flow after cardiac contraction ends.
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This Windkessel effect limits excessive systolic pressure rises and sustains diastolic pressure, reducing cardiac afterload and maintaining coronary perfusion.
Myocyte and sarcomere structure
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Myocytes are joined by intercalated discs.
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The schematic describes longitudinal and transverse tubules extending from the sarcoplasmic reticulum within myocytes.
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Sarcomeres contain thick filaments composed of myosin and thin filaments composed primarily of actin.
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Actin filaments contain troponin, tropomyosin and actin subunits.