2. Cardiovascular System- Heart Actions

function in

synctium

systole

contraction of a heart chamber

diastole

relaxation of a heart chamber

cardiac cycle

atria contract (ventricles relax), ventricles contract (atria relax), both chambers briefly relax

cardiac muscle cells

connected by intercalated discs

gap junctions

allow ions to flow between cells in the heart

heart functional units

one in atria, one in ventricle, let atria contract first, and ventricles follow

heart cells are separate

but work as a team as one functional unit

cardiac conduction

SA node → atrial synctium → junctional fibers → AV node → AV bundle → bundle fibers → purkinje fibers → ventricular synctium

SA node

pacemaker, initiates rhythmic contractions of the heart

internodal atrial muscle

conducts impulse from SA node to atria

AV node

conducts impulses to AV bundle, delays impulse so atria finishes contracting before ventricles

AV bundle

conducts impulses rapidly between SA node and bundle branches

left and right bundle branches

split off from AV bundle, conduct impulses to purkinje fibers on both sides of the heart

purkinje fibers

large fibers that conduct impulses to ventricular myocardium, conduct impulses to apex first, whorled pattern of muscle in ventricles contract with twisting motion

electrocardiogram

deflections in normal ECG or waves include P wave, QRS complex, T wave

P wave

atrial depolarization → atria contract

QRS complex

3, ventricular depolarization → ventricles contract

Q

downward deflection

R

large, upward, triangular spike

S

downward deflection

T wave

ventricular repolarization → ventricles relax

heart sounds

lubb-dupp

lubb

first sound, occurs during ventricular systole, closing of AV valves

dupp

second heart sound, ventricular diastole, closing of pulmonary and aortic semilunar valves

murmur

abnormal heart sound derived from incomplete closure of cusps of a valve

blood flows from

high pressure to low pressure

pressure differences in chambers

open and close heart valves

ventricles diastole

pressure is low, AV valves are open, blood enters, volume increases

contraction begins

ventricles squeeze, pressure rises, AV valves close (briefly all valves are close), volume stays the same

ventricles ejection

pressure exceeds pressure in arteries, opens semilunar valves, blood leaves, volume decreases

ventricles relax

pressure falls, semilunar valves close, volume stays same until filling again

regulation of cardiac cycle

heart rate and volume of blood pumped change to meet requirements

cardiac center

in medulla oblongata performs neural regulation of heart

heart rate changes occur

due to factors that influence SA node

sympathetic and parasympathetic fibers modify heart rate in response to changing conditions such as

physical exercise, body temp, fight or flight

parasympathetic impulses

reach heart via vagus nerve, cardioinhibitory, lower SA node rate of 100 to 60-80, decrease heart rate due to influence on SA and AV

sympathetic impulses

reach heart on accelerator nerves, cardioacceleratory, increase heart rate due to influence on SA and AV nodes, atrial and ventricular myocardium

baroreceptor reflex responses

baroreceptors in aortic arch and carotid artery sinuses detect blood pressure, increase pressure stretches receptors, parasympathetic cardio inhibitory reflex lowers heart rate and blood pressure

stretch receptors in venae cavae

increase in blood pressure stretches receptors, sympathetic cardioaccelerator reflex increases heart rate and force of contraction to lower venous pressure