The Heart Circuits Chambers Valves (one-way-flow) Myocardiocytes

Volumes? Pressures? heart –> lungs –> heart heart –> body –> heart Volumes? Pressures?

The Circulatory system is a "closed circulation" Systemic Circuit Pulmonary Circuit Systemic Circuit Artery = Vein =

Heart valves prevent back (retrograde) The Heart has 4 Valves Heart valves prevent back (retrograde) flow of blood. There are 2 atrioventricular valves (AV) – found between the atria and ventricles. 1) Right AV (tricuspid) valve 2) Left AV (bicuspid/mitral) valve

There are 2 semilunar valves – found between the ventricle and the artery they leave, 1) Aortic semilunar valve 2) Pulmonary semilunar valve Two heart sounds: “Lub” and “Dup” 1. Closure of AV valves = “Lub” 2. Closure of Semilunar valves = “Dup”

Disorders of Heart Valves Stenosis - Prolapse - Can lead to abnormal Heart sounds, e.g., heart murmurs. Indicates: 1) turbulence 2) retrograde flow

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Graded Contraction of Heart Force generated by myocardiocyte contraction is: 1. Proportional to amount of Calcium ions (Ca2+)  [Ca2+] => more crossbridges, more force & speed.

Graded Contraction of Heart Force generated by myocardiocyte contraction is: 1. Proportional to amount of Calcium ions (Ca2+)  [Ca2+] => more crossbridges, more force & speed. 2. Modulated by Autonomic N.S. => Sym  HR and Force => Para  HR

Sympathetic – speeds heart rate by  Ca2+ influx. Parasympathetic – slows rate by  K+ efflux,  Ca2+ influx.

Graded Contraction of Heart Force generated by myocardiocyte contraction is: 1. Proportional to amount of Calcium ions (Ca2+)  [Ca2+] => more crossbridges, more force & speed. 2. Modulated by Autonomic N.S. => Sym  HR and Force => Para  HR 3. Stretch-Length-Tension Relationship  stretch, =>  Ca2+ entering =>  contraction force

Factors Influencing Stroke Volume

Electrical Conduction System Sino Atrial (SA) Node Atrial Ventricular (AV) Node AV Bundle (of His) L and R Bundle Branches Purkinje Fibers

Mechanical Events of the Heart The Cardiac Cycle Mechanical Events of the Heart Late Diastole: “Heart at rest” all chambers relaxed filling with blood (passive filling ~ 80% full). 2. Atrial Systole: atria contract, adds the last 20% of blood to ventricles (top off ventricles) Occurs after P-wave on EKG End Diastolic Volume (EDV) = Maximum ventricular volume

3. Ventricular Systole (part 1): Ventricular contraction begins - Pressure (P). Closure of AV valves = 1st heart sound ("lub") Sealed Compartment – all valves are closed. Isovolumetric ventricular contraction: => pressure builds as volume stays the same.

4. Ventricular Systole (part 2): Ejection phase: P pushes open semilunar valves, blood forced out into artery leaving ventricle. Pulmonary Semilunar => 25 mmHg (minimum pressure) Aortic Semilunar => 80 mmHg (minimum pressure) End Systolic Volume (ESV) = volume remaining in heart after ejection (~½). Stroke Volume = EDV - ESV (ml/beat)

The AV valves then open, refilling starts – 5. Ventricular Diastole: Relaxation of ventricles, artery back flow slams semilunar valves shut = 2nd heart sound ("dup"). Sealed Compartment again – all valves are closed. Isovolumetric ventricular relaxation: =>  pressure as volume stays the same. The AV valves then open, refilling starts – back to start of cycle.

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