Cardiac Physiology

heart

2 pump transportation system (blood vessels are delivery route)

mediastinum

middle cavity of thoracic cavity where heart is positioned

pulmonary circulation

consists of blood vessels that carry deoxygenated blood to and from the lungs (pumped by right side)

systemic circulation

consists of blood vessels that carry oxygenated blood to and from the body tissues (pumped by left side)

upper chambers of the heart

atria

lower chambers of the heart

ventricles

where does the right side of the heart pump blood to?

pulmonary circulation; receives deoxygenated blood from the body —> pumps to the lungs for reoxygenation

where does the left side of the heart pump blood to?

systemic circulation; receives preoxygenated blood —> pumps it to the body

3 membranes enclosing heart

pericardium, epicardium, pericardial cavity

pericardium

outer layer, double-walled, connective tissue sac; protects heart, anchors it to surrounding structures

epicardium

lays directly against the heart

pericardial cavity

space between pericardium and epicardium filled with serous fluid; reduces friction as heart pumps

pericarditis

inflammation of pericardium; roughens membrane surfaces, causing pericardial friction rub heard with stethoscope

cardiac tamponade

excess fluid that leaks into pericardial space, can compress heart’s pumping ability; treated by drawing fluid out of cavity

myocardium

cardiac muscle; forms bulk of the heart; arranged around each atria, designed to squeeze blood into ventricles when contracted; arranged in both ventricles, designed to squeeze blood into different circulatory systems

endocardium

connective tissue layer on the inner myocardium surface; lines heart’s chambers and valves, makes up valves that separate the atria from the ventricles

atria

receiving chambers of the heart, separated by interatrial septum, receive blood from venous system and push it inferiorly to the ventricles; thin walls —> minimal contraction to push blood into ventricles

right atria

receives blood from superior and inferior vena cava and coronary sinus; weaker than left atrium, higher oxygen content in blood

left atria

receives blood from pulmonary veins, stronger than right atrium

which atrium is stronger, right or left?

left

ventricles

discharging chambers; located at apex, separated by interventricular septum; receives blood from atria and pushes it to the lungs (R) or rest of body (L); thick-walled chambers (need to contract forcefully to overcome vascular resistance/friction)

is the left or right ventricle thicker?

left; there is more force counteracting it from the body than the lungs

right ventricle

pushes blood through the pulmonary trunk to the left and right pulmonary arteries

left ventricle

pushes blood through the aorta

do valves open in the opposite direction?

no— valve are one-way

what causes blood to travel one direction in the heart?

4 valves open/close in response to blood pressure on either side preventing backflow

atrioventricular (AV) valves

located between the atria and ventricles; tricuspid and mitral valves

tricuspid valve

between right atrium and ventricle

mitral valve

between left atrium and ventricle

what connects the atrioventricular valves to the ventricular wall?

chordae tendinae (connective tissue strings made of endocardium, anchor cusps of valves to the papillary muscles to keep them from folding backwards after contractions)

semilunar valves (SV)

located between the ventricles and between the major arteries

pulmonary SV valve

between the right ventricle and pullmonary trunk

aortic SV valve

between left ventricle and aorta

what allows arteries to stay closed?

blood pressure in arteries

what is the first heart sound?

closing of AV valves at beginning of ventricular systole

what is the second heart sound?

closing of SL valve at the beginning of ventricular diastole

what does the pause between the lub-dub sounds indicate?

heart relaxation

mitral valve closes slightly ____________ tricuspid

before

aortic valve closes slightly before ___________ valve

pulmonary

heart murmur

abnormal heart sounds heard when blood hits obstructions; indicates valve problems

incompetent/insufficient valve (heart murmur)

fails to close completely, allowing backflow of blood

stenotic valve (heart murmur)

fails to open completely, restricting blood flow through valve

intercalated discs

connect cardiac muscle fibers

desmosomes

prevent adjacent cells from separating during contraction

gap junctions

allow ions to pass quickly from cell to cell

functional syncytium

myocardium behaves as a single coordinated unit

describe cardiac muscle contraction

all or nothing, longer absolute refractory period, longer contraction phase, shorter relaxation cycle; tetanus not possible

energy source for cardiac muscle

more mitochondria, higher O2 dependence, special shuttles in cardiac mitochondria recycle lactic acid and use it for energy

cardiac muscle contracts without __________ input.

neuronal

automaticity

heart contracts rhythmically by its ability to generate its own action potentials (myogenic); rate of rhythm is altered by ANS

autorhythmic cells

initiate and conduct action potentials responsible for contraction of working cells

99% of cardiac muscle cells are ___________.

contractile

pacemaker potential

slow depolarization due to opening of Na+ channels and closing of K+ channels

cardiac muscle action potentials have __________ which is not seen in skeletal muscle contraction

plateau

how long does action potential last in cardiac muscle?

200ms

benefits of longer action potential and contraction in cardiac autorhythmic cells

sustained contraction ensures efficient ejection of blood, longer refractory period prevents tetanic contractions

where are pacemaker cells located?

SA node

________ cells generate action potential faster than any other heart cell

pacemaker

bundle of his

conducts action potential from AV node to interventricular septum, where it splits into left and right bundle branches

function of left and right bundle branches

propagate action potential through interventricular septum to heart apex

purkinje fibers

spread action potentials from apex to left and right ventricles rapidly due to their high proportion of intercalated discs

internodal pathways

conduct action potential from SA node to myocytes in the atria through gap junctions

spread of cardiac excitation is ________ to ensure efficient _________

coordinated/pumping

what must happen before ventricular contraction onset?

atrial excitation and contraction

electrocardiogram (ECG)

measures electrical activity of the heart by measuring voltage differences between regions; composed of all action potentials at given time

p-wave

depolarization (contraction) of atria

QRS complex

depolarization of ventricles

Q wave (QRS complex)

depolarization of the septum

R wave (QRS complex)

depolarization of the anterior wall

S wave (QRS complex)

depolarization of the inferior wall

T wave

repolarization (relaxation of the ventricles)

ectopic focus

abnormal pacemaker that takes over pacing

defective SA node may cause ____________.

ectopic focus

extrasystole

premature contraction; ectopic focus of small region of heart that triggers impulse before SA node can, causing delay in next impulse

pacemakers make up ____% of myocytes

1

99% of myocytes are ____________ cells.

contractile

if AV node takes over, it sets ______________________ at 40-60bpm

junctional rhythm

if AV node is defective, it may cause a ___________

heart block

arrhythmia

irregular heart rhythm; uncoordinated atrial and ventricular contractions

fibrillation

rapid irregular contraction

treatment of fibrillation

defibrillation— interrupts chaotic twitching, giving heart “clean slate” to start regular, normal depolarization

_________ events always follow the electrical events

mechanical

mechanical events always follow the ____________ events

electrical

systole

periods of contraction and emptying of the heart’s chambers; right after QRS complex for ventricles

heart spends _______ time in systole (fraction)

1/3

diastole

periods of relaxation and filling of the heart’s chambers; for atria, occurs during QRS (can’t see it), for ventricles, occurs right after T wave

what ions are moving during repolarization of cardiac pacemaker cell?

Ca2+ channels are inactivated and K+ channels open, allowing K+ efflux

changes in patterns or timing of ______ may reveal diseased or damaged heart/problems with heart’s conduction system

ECG

enlarged R waves may indicate:

enlarged ventricles

elevated/depressed S-T segment indicates:

cardiac ischemia

prolonged Q-T interval reveals:

abnormality that increases risk of ventricular arrhythmias

cardiac cycle

all events associated with blood flow through the heart during one complete heart beat

the cardiac cycle is marked by a succession of ____________ and _____________ changes within the heart’s chambers

pressure/volume

3 phases of the cardiac cycle

1. ventricular filling (mid-late diastole)

2. ventricular systole (atrial diastole)

3. isovolumetric relaxation (early diastole)

describe phase 1 of the cardiac cycle: ventricular filling

blood is returning from circulation, flowing passively from atria through open AV valves into ventricles; aortic and pulmonary valves are closed, atrial systole occurs (P wave), atria contract —> pushing blood up into ventricles; ventricles are in diastole and filled to their maximal volume

describe phase 2 of the cardiac cycle: ventricular systole

atria relax, ventricles begin to contract (QRS complex), ventricular pressure rises rapidly as myocardium begins to contract & close the AV valves; constant blood volume

describe the movement of ions during the plateau phase of contractile cardiac muscle cell AP

slow Ca2+ influx through slow Ca2+ channels, most K+ channels closed (cell is depolarized)

describe phase 2 of the cardiac cycle: isovolumetric relaxation

ventricles relax (T wave), ventricular pressure decreases rapidly, blood flows back into pulmonary valve and aorta, passive filling begins in ventricles (restarts phase 1)

end systolic volume

blood that remains in the ventricles after contraction

muscle tension develops during the ___________ and peaks just after the _________ ends

plateau x 2