HEART AS A PUMP

Learning objecves

1. Describe the structure and funcon of the heart chambers and associated valves. 2. Explain systole and diastole. 3. Explain the cardiac cycle and associated heart sounds. 4. Explain Pressure-Volume loops, stroke volume and cardiac output.

HEART CHAMBERS

lung Right atrium base

Le ventricle

Right ventricle apex CARDIAC VALVES • Four cardiac valves prevent backflow.

• Pulmonary and aorc valves prevent back flow from the arteries into the relaxing ventricles.

• Passive response to pressure gradients. Pulmonic & aorc valves open when the myocardium contracts and close with relaxaon.

• AV valves (mitral and tricupsid) experience high pressure. These valves are tethered to the ventricle wall (papillary muscle) via tendon like cords (chordae tendineae) to prevent eversion.

CARDIAC CYCLE

Diastole: Ventricles relax Relaxaon AV valves open & filling Ventricle fills AV valves close

Isovolumic Relaxaon Isovolumic contracon

All valves Systole: close Aorc valve & Contracon & ejecon pulmonic valves open of blood Ejecon of blood CARDIAC CYCLE

By DanielChangMD revised original work of DesnyQx; Redrawn as SVG by xavax. hp://commons.wikimedia.org/wiki/File:Wiggers_Diagram.svg

PRESSURE-VOLUME LOOP

200 A = AV valve opens A-B = filling

100 D B = End diastolic volume (EDV); AV valves closes C B-C = isovolumic contracon

Pressure (mmHg) B A C = Aorc valve opens C-D = ejecon 50 100 150 Volume (ml) D = End systolic volume (ESV); Aorc valve closes D-A = isovolumic relaxaon CARDIAC PERFORMANCE

• Arterial pressure is determined in part by the rate blood flows from the arterial system through capillaries to the venous system. Cardiac pumping changes to match ssue needs.

• End-diastolic volume (EDV) in each ventricle is 125 ml.

• During one systole, the volume of blood ejected is the stroke volume (SV). SV is usually 70 mls.

• Not all blood in the ventricle is ejected. The volume remaining is the end-systolic volume (ESV). This is usually 55 mLs.

SV = EDV- ESV CARDIAC OUTPUT

• Cardiac output (CO) = volume pumped each minute.

• CO depends on the heart rate (HR) & stroke volume (SV).

CO = SV X HR

• HR is typically 72 beats per min and SV = 70 ml, so

CO = 5 L/min

KEY CONCEPTS

• The heart consists of two separate pumps. Blood moves in a unidireconal manner from the right heart to the lung for gas exchange, then returns to the le heart from which it is pumped to the systemic circulaon for delivery to ssues. • Each beat of the heart (cardiac cycle) starts with electrical acvaon of the atria then of the ventricles. The sequence is the same for the right and le chambers! • Ventricular contracon and ejecon occur during systole. The beginning of the systole coincides with the first heart sound and ends with the second heart sound. • Ventricle relaxaon and filling occur during diastole. Diastole begins with second heart sound and ends with the first heart sound. • The volume of blood ejected with each beat is the stroke volume. • The sum of the stroke volumes ejected in one minute is the cardiac output (CO).