Part D-Cardiac Cycle, Action Potential, and Heart Sounds

cardiac cycle

A complete heartbeat consisting of contraction and relaxation of both atria and both ventricles

Cardiac Cycle: Systole

contraction phase

Cardiac Cycle: Diastole

relaxation phase

when atria contract

atrial systole

-ventricles relax ( ventricular diastole)

when ventricles contract

ventricular systole

-atria relax (atrial diastole)

end of cardiac cycle

atria and ventricles briefly both relax

right atria contracts

-left atria contracts, right ventricle relaxes

right ventricle contracts

-right atria relaxes, left ventricle contracts

atria contract and ventricles relax

when blood is forced into ventricles

atria and ventricles relax

when blood flows passively into the atria and then passively into the ventricles

Pressure during contraction

blood flows from areas of high pressure to low

-controlled by timing of contractions

-directed by one way valves

atrial systole

atrial contraction, AV valves open and blood is ejected into ventricles

ventricular systole and atrial diastole

Atrial systole ends

Atrial diastole begins

Ventricles contain maximum blood volume

Ventricles contract and build pressure

Closing AV valves

Producing isovolumetric contraction

ventricular systole

ventricles contract, opening semilunar valves and blood flows from ventricles to pulmonary trunk and aorta

-semilunar valves then close

ventricular diastole

-isovolumetric relaxation (all valves are closed)

-AV valves open and ventricles fill

isovolumetric relaxation

All heart valves are closed

Ventricular pressure is higher than atrial pressure

Blood cannot flow into ventricles

atrial damage

individuals can survive

ventricular damage

can lead to heart failure

increased heart rate

all phases of cardiac cycle are shorten, especially diastole

BP systole

contraction phase, increases BP

BP diastole

relaxation phase, decreases BP

action potential

cardiomyocytes have a stable resting potential of -90mV, and depolarize only when stimulated

phases of action potential

depolarization, plateau, repolarization

Depolarization

-Na+ gates open and Na+ rushes in, membrane depolarizes quickly.

-action potential peaks at +30mV

-Na+ gates close quickly

Plateau

-200-250ms-sustains contraction

-Ca+ gates open and Ca+ rushes in

-Ca+ binds to troponin on SR, triggering contraction

Repolarization

-Ca+ gates close and K+ channels open

-K+ rushes out of the cell, returning the cell to resting potential

absolute refractory period

cardiac muscles cells cannot respond

-250ms, prevents wave summation and tetanus

relative refractory period

cells respond only to strong stimuli

Summation or treppe

addition of a second twitch, resulting in greater tension, and it results from stimulation the muscles before it has a chance to relax completely

tetany

prolonged contraction without relaxation and results from repeating stimulation before the muscle has had a chance to relax

regulates cardiac cycle

-Potassium - ion concentrations

-calcium - ion concentrations

potassium

affects electrical potential of cell membrane altering its ability to reach threshold for conduction an impulse

Hyperkalemia

decreases rate and force of contraction, may block conduction of cardiac impulses and heart may suddenly stop

Hypokalemia

heart may develop life threatening arrhythmia

calcium

helps initiate muscle contraction

Hypercalcemia

increases heart action and possible danger of heart undergoing prolonged contraction

Hypocalcemia

depresses heart action

heart sounds

due to closing of valves

-detected with a stethoscope

S1

lub-AV valves closing

-occurs during ventricular systole

S2

dup-semilunar valves closing

-occurs during ventricular diastole

murmur

abnormal heart sound, blood leaks back through valves d/t leaky or incompetent closure of heart valves