Cardiovascular Physiology: Foundations → ECG → Cardiac Cycle → Hemodynamics → BP regulation

When does the fetal heart begin acting as an electrochemical pump?

After 4 weeks of gestation

What are the three components of the circulatory system?

Heart blood vessels and blood

Primary function of the heart

Establishes pressure gradient for blood flow

Primary function of blood vessels

Distribution of blood throughout the body

Primary function of blood

Transport medium for O2 CO2 nutrients wastes electrolytes and hormones

What are the two vascular circuits?

Pulmonary circulation and systemic circulation

Pulmonary circulation definition

Closed loop carrying blood between heart and lungs

Systemic circulation definition

Carries blood between heart and all body tissues

Pulmonary circulation pressure type

Low pressure low resistance

Systemic circulation pressure type

High pressure high resistance

Heart location

Mediastinum of thoracic cavity

Heart size comparison

Approximately the size of a clenched fist

Why is the heart considered a dual pump?

Right and left sides pump blood separately

Upper chambers of the heart

Atria

Lower chambers of the heart

Ventricles

Function of atria

Receive blood returning to the heart

Function of ventricles

Pump blood away from the heart

Vessels returning blood to heart

Veins

Vessels carrying blood away from heart

Arteries

Function of septum

Prevents mixing of oxygenated and deoxygenated blood

Blood entering right atrium source

Systemic circulation via vena cavae

Blood entering right atrium oxygen level

Oxygen poor

Blood leaving right ventricle destination

Pulmonary circulation via pulmonary artery

Blood returning to left atrium source

Pulmonary veins

Blood entering left ventricle oxygen level

Oxygen rich

Main artery leaving left ventricle

Aorta

Why is left ventricular wall thicker?

Higher pressure and resistance workload

Direction of blood flow through heart

Veins atria ventricles arteries

Purpose of heart valves

Ensure unidirectional blood flow

How do valves open?

Forward pressure gradient

How do valves close?

Backward pressure gradient

Right AV valve name

Tricuspid valve

Left AV valve name

Bicuspid or mitral valve

Function of chordae tendineae

Prevent valve eversion

Papillary muscle function

Anchor AV valve chordae

Semilunar valves

Aortic and pulmonary valves

When do semilunar valves open?

During ventricular contraction

When do semilunar valves close?

During ventricular relaxation

Why no valves between atria and veins?

Low atrial pressure and vein compression

Heart fibrous skeleton function

Supports valves and electrically separates atria and ventricles

Layers of heart wall

Endocardium myocardium epicardium

Main contractile layer of heart

Myocardium

Arrangement of cardiac muscle fibers

Spiral arrangement

Result of spiral contraction

Wringing motion apex to base

Intercalated discs function

Mechanical and electrical coupling

Two junctions in intercalated discs

Desmosomes and gap junctions

Role of gap junctions

Spread action potentials

Cardiac muscle syncytium meaning

Cells function as a single unit

Endocrine function of heart

Secretion of ANP and BNP

Hormonal effect of ANP and BNP

Decrease blood volume and blood pressure

Pericardial sac layers

Fibrous outer and serous inner

Function of pericardial sac

Protect/ anchor and lubricate the heart

Autorhythmicity definition

Ability to generate action potentials spontaneously

Two cardiac muscle cell types

Contractile and autorhythmic

Percentage of contractile cells

99 percent

Primary pacemaker of heart

SA node

Order of intrinsic firing rates

SA node AV node His Purkinje

Normal heart rate source

SA node at 60 bpm

AV node takeover heart rate

Slower than SA node

Complete heart block effect

Atria and ventricles beat independently

Pacemaker potential definition

Slow depolarization to threshold

Key ions in pacemaker potential

Na influx decreased K efflux Ca influx

If channel function

Opens during hyperpolarization

Pacemaker AP phases

4 0 3

Phase 4 pacemaker event

I_f channels open causing a slow influx of Na+ ; decrease in K+ efflux,

Phase 0 pacemaker event

Ca influx via L type channels

Phase 3 pacemaker event

Ca2+ channels close, K+ channels open. K+ efflux membrane potential becomes more negative (repolarization)

Slope of phase 4 determines

Heart rate

Cardiomyocyte resting membrane potential

-90 mV

Ventricular AP phases

4 0 1 2 3

Phase 0 ventricular AP

Fast Na influx

Phase 2 ventricular AP

Ca plateau prevents tetany

Phase 3 ventricular AP

L-type Ca2+ channels close, K+ efflux dominates (repolarization)

Purpose of cardiac plateau

Prolong refractory period, prevents tetany, allows ventricular filling

Absolute refractory period meaning

No stimulus can cause AP

Effective refractory period meaning

Only local response possible

Relative refractory period meaning

Strong stimulus causes AP

Excitation contraction coupling mechanism

Calcium induced calcium release

Role of SERCA pump

Reuptake Ca into SR

ECG definition

Surface recording of cardiac electrical activity

P wave

Atrial depolarization

QRS complex

Ventricular depolarization

T wave

Ventricular repolarization

PR interval

Atrial depolarization plus AV nodal delay

ST segment

Ventricular plateau phase

Lead definition

View of electrical activity from direction

Number of limb leads

Six

Most clinically important lead

Lead II

Einthoven law

Lead II equals Lead I plus Lead III

Cardiac cycle definition

Sequence of mechanical events per heartbeat

Two main phases of cardiac cycle

Diastole and systole

S1 heart sound

AV valve closure

S2 heart sound

Semilunar valve closure

S3 heart sound

Rapid passive ventricular filling

S4 heart sound

Atrial contraction into stiff ventricle

Stroke volume formula

EDV minus ESV

Ejection fraction formula

SV divided by EDV

Cardiac output formula

Heart rate times stroke volume

Normal cardiac output value

Approximately 5 L per minute

Frank Starling law

Increased filling increases contraction force