The pressure that must be overcome before a semilunar valve can open is the

The pressure that must be overcome before a semilunar

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The pressure that must be overcome before a semilunar valve can open is the afterload Ejection of blood from heart begins when pressure in right ventricle exceeds pressure in pulmonary trunk and when pressure in left ventricle exceeds pressure in aorta At that point, the higher pressure in ventricles causes blood to push semilunar valves open
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NS regulation of heart originates in cardiovascular center in medulla oblongata This region receives input from sensory receptors and from higher brain centers (cerebral cortex) Cardiovascular center then directs appropriate output by increasing or decreasing frequency of nerve impulses in autonomic nervous system
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Hormones Epinephrine and norepinephrine (from adrenal gland) enhance heart’s pumping effectiveness Increase both heart rate and contractility Exercise, stress, and excitement cause adrenal gland to release more hormones Thyroid hormones – increases heart rate and contractility One sign of hyperthyroidism (excess thyroid hormone) is tachycardia ( elevated resting heart rate)
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Cations Sodium and potassium are crucial for production of action potentials Elevated blood levels of potassium or sodium decreases heart rate and contractility Excess sodium blocks calcium inflow during cardiac action potentials, thereby decreasing force of contraction Excess potassium blocks generation of action potentials (can cause bradycardia, slowing down of heartbeat) Moderate increase of calcium speeds heart rate and strengthens heartbeat
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Newborn baby has resting heart rate over 120 beats/min, rate then gradually declines throughout life Adult females often have slightly higher resting heart rates than males Regular exercise tends to bring resting heart rate down in both genders bradycardia – resting heart rate under 50 beats/min Beneficial in endurance type training because slower heart rate is more energy efficient than one that beats more rapidly
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  • Fall '16
  • Lambrini Nicopoulos
  • right ventricle

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