HEART PHYSIOLOGY

What a Job!

It pushes your six liters of blood through your blood vessels over 1000 times a day!

Thousands of cells function as one unit!

Basic Heart Anatomy

Note: Right & left are named based on position in the chest & seem reversed in a diagramSuperior chambers = atria

Small, limited muscleInferior chambers = ventricles

Large, heavily muscled Pumping chambers

Septum divides ventricles

Valves

Prevent back-flow of blood Two atrioventricular (AV) valves:

Tricuspid Bicuspid/mitral

Two semilunar valves: Pulmonary Aortic

Purpose?

Pulmonary circuit Between heart & lungsWhy?What is the pump?

Systemic circuit Between heart & rest of

bodyWhy?What is the pump?

Right Atrium

Receives deoxygenated blood from Superior vena cava (from

body above diaphragm) Inferior vena cava (from

body below diaphragm) Coronary sinus (from heart)

Passes blood through tricuspid valve to RV

Left Atrium

Receives oxygenated blood from lungs through: Right and left superior

pulmonary veins Right and left inferior

pulmonary veins Passes blood through the

bicuspid/mitral valve to the LV

Ventricles

RV pumps deoxygenated blood to lungs through pulmonary semilunar valve into pulmonary trunk

LV pumps oxygenated blood to body through aortic semilunar valve to aorta

Cardiac Cycle = one heartbeat

Systole – contraction of the ventricles Diastole – relaxation of the ventricles Events occur in 3 phases:

1: Mid-to-Late Diastole

Heart in complete relaxation Low pressure Blood flowing into atria and ventricles Semi-lunar valves closed A-V valves open

ENDEND – atria contract and force remaining blood into ventricles

2: Ventricular Systole

Ventricles contract, increasing pressure

A-V valves close Atria begin filling with blood

ENDEND – Ventricular pressure > artery

pressure Blood forced out semilunar valves

3. Early Diastole

Ventricles relax, dropping pressure

Semi-lunar valves close

ENDEND – Atrial pressure > ventricular

pressure Blood is forced through AV valves

Heart Rhythm

1. Intrinsic Conduction System (ICS) – “specialized” tissue sets basic rhythm, ~75 beats/minute

2. Extrinsic Control – nervous system can increase or decrease heart rate

Intrinsic Conduction System

Starts with autorhythmic cells:

1. SA (sinoatrial) Node – “Pacemaker” - causes the atria to contract

2. AV (atrioventricular) Node – causes ventricles to contract

Continues through rest of ICS:

3. Bundle of His4. Bundle branches5. Purkinje fibers

Depolarization Sequence

1

2

43

5

Electrocardiogram [ECG/EKG]

Traces the flow of current through the heart

Cardiac Output

Stroke Volume (SV) – Blood pumped per ventricle per heartbeat

Cardiac Output (CO) – Blood pumped per ventricle per minute

= Heart Rate (HR) * Stroke Volume (SV)

Normal Adult HR is ~75 beats/minuteAverage resting SV is ~70 ml/beat

What is the average adult CO?

Irregular Heartbeats

Tachycardia (>100 beats/min)

Bradycardia (<60 beats/min)

Ischemia – lack of adequate blood supply

Fibrillation – rapid uncoordinated shuddering of heart muscle (major cause of heart attack/death)