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

• Circuits

• Chambers

• Valves(one-way-flow)

• Myocardiocytes

The Heart

Volumes? Pressures?

heart –> lungs –> heart

heart –> body –> heart

Artery = Vein =

Trace a RBC!

The Heart has 4 ValvesTo 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 valvesbetween 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”

http://www.openheartsurgery.com/heart_murmur.html

Normal Heart Valves Problems Opening:

Stenosis – narrowing of valve, when a valve doesn't open completely.

Turbulence = noise = murmur.

Problems Closing: Prolapse –overlapping or when valve doesn't close tightly. Also termed valvular insufficiency (regurgitation) Retrograde flow = noise = murmur.

Disorders of Heart Valves

Problem Heart Valves

Myocardiocytes:1) Autorhythmic

2) Contractile

Action Potentials for Autorhythmic Myocardiocytes

stimulus

Action Potentials for Contractile Myocardiocytes

Myocardiocytes: Calcium induced Calcium release

Graded Contraction of HeartForce 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:

2. Modulated by Autonomic N.S.

=> Sym HR and Force

=> Para HR

1. Proportional to amount of Calcium ions (Ca2+) [Ca2+] => more crossbridges, more force & speed.

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:

2. Modulated by Autonomic N.S.

=> Sym HR and Force

=> Para HR

1. Proportional to amount of Calcium ions (Ca2+) [Ca2+] => more crossbridges, more force & speed.

3. Stretch-Length-Tension Relationship

stretch, => Ca2+ entering => contraction force

Factors Influencing Stroke Volume

The Cardiac Cycle

http://www.youtube.com/watch?v=rguztY8aqpk

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 = 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)

5. Ventricular Diastole:

Relaxation of ventricles, artery back flow slams

semilunar valves shut = 2nd 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.

Cardiac Output (C.O.)

= Heart Rate x Stroke Volume

*Heart Rate = beats/min

*Stroke Volume = EDV-ESV (vol/beat)

e.g. calculation:

Electrical Conduction System

Sino Atrial (SA) Node

Atrial Ventricular (AV) Node

AV Bundle (of His)

L and R Bundle Branches

Purkinje Fibers

Trace of an ElectroCardioGram (ECG)

The ECG

P wave:

PR interval:

QRS complex:

T wave:

Ventricular Assist Devices

http://www.youtube.com/watch?v=D3ZDJgFDdk0