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

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

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

Trace a RBC!

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

2 semilunar valves between a ventricle and artery. 1) Aortic semilunar valve 2) Pulmonary semilunar valve Two heart sounds: “Lub” and “Dup” 2. Closure of Semilunar valves = “Dup” 1. Closure of AV valves = “Lub”

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

stimulus

Myocardiocytes: Calcium induced Calcium release

Graded Contraction of Heart Force generated by myocardiocyte contraction is: 1. Proportional to amount of Calcium ions (Ca 2+ )  [Ca 2+ ] => more crossbridges, more force & speed.

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

Sympathetic – speeds heart rate by  Ca 2+ influx. Parasympathetic – slows rate by  K + efflux,  Ca 2+ influx.

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

Factors Influencing Stroke Volume

The Cardiac Cycle

1.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 The Cardiac Cycle Mechanical Events of the Heart End Diastolic Volume (EDV) = Maximum ventricular volume

3. Ventricular Systole (part 1): Ventricular contraction begins -  Pressure (P). Closure of AV valves = 1 st 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)

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

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

The ECG P wave: PR interval: QRS complex: T wave: