Cardiac Physiology-03

Question 1

myocardium

Answer 1

responsible for pumping action, striated involuntary muscle, fibers swirl diagonally around the heart in bundles; the heart wrings blood out of the ventricles

Question 2

functional syncytium

Answer 2

merging cells performing as a unit; those of the heart are joined electrically

Question 3

myocytes

Answer 3

form a functional syncytium; in b/w adjacent cells, cardiac cells have branching patterns (Y shapes, Z shapes)

Question 4

intercalated discs

Answer 4

specialized connections between myocardial cells containing gap junctions and desmosomes

Question 5

desmosomes

Answer 5

help structurally glue adj. myocytes together; so when one contracts the other contracts + are pulling on e/o to transmit force to blood contained within ventricle

Question 6

gap junctions

Answer 6

each half of a gap junction is formed in one cell and the other; functions to allow ions to move freely b/w these cells to electrically connect them

• when AP is generated within myocyte in apex, AP spreads like propagated wave through each adjacent myocyte up to base of heart
• wave of contraction occurs from apex to base

Question 7

SA node

Answer 7

back of right atrium, opening for SVC; where pacemaker cells are found constantly depolarizing, stim. resting HR spontaneously, AP spreads as a wave across all myocytes of atrium to spread across L and R atrium

Question 8

AV node

Answer 8

base of RA, pacemaker cells depolarize slower, wave slows down when AP reaches this point; fewer gap junctions, gives time to allow atria to contract and send blood to ventricles before electrically stimulating ventricles

Question 9

AV bundles (bundle of His)

Answer 9

straddles fibrous skeleton, allows an electrical signal to go from atria to ventricles

Question 10

R and L bundle branches

Answer 10

stim. various regions of ventricle to ensure L and R ventricles contract simultaneously

Question 11

phases of an AP in a ventricular myocyte

Answer 11

depolarization, plateau, repolarization, refractory period

Question 12

depolarization phase

Answer 12

AP generated by pacemaker cell makes myocyte reach threshold; opening of voltage-gated sodium channels

Question 13

plateau phase

Answer 13

voltage-gated potassium and calcium channels open (K+ out, Ca2+ in for stim./regulating contraction)

Question 14

repolarization

Answer 14

when Ca2+ channels close and K+ channels stay open, depolarization back to RMP occurs; also assisted by sodium-potassium KTPase

Question 15

refractory period

Answer 15

another cardiac AP cannot be generated; always longer than contraction phase b/c heart needs to relax to allow it to fill up

Question 16

electrocardiogram

Answer 16

a composite record of APs produced by all the heart muscle fibers, detected at the surface of the body, 3 recognizable waves (P, QRS, and T), electrical event precedes mechanical event (takes time for AP to propagate to stim. myocardiocytes to cause them to release CA2+ to contract)

Question 17

P wave

Answer 17

atrial depolarization

Question 18

PQ segment

Answer 18

atrial contraction; slowing of AP conduction at AV node (smaller fibers; less gap junctions)

Question 19

QRS complex

Answer 19

ventricular depolarization (and atrial repolarization); large amplitude due to amount of muscle in ventricles generating larger electrical signal

Question 20

ST segment

Answer 20

systolic contraction continues

Question 21

T wave

Answer 21

ventricular repolarization

Question 22

after T wave

Answer 22

ventricular diastole (relaxation)

Question 23

cardiac pressure

Answer 23

BP produced by contraction of heart; only present on arterial side of system and measured w/ sphygmomanometer

Question 24

dicrotic wave

Answer 24

second wave that occurs when aortic valve closes

Question 25

S1 sound

Answer 25

AV valve closure; ventricle starts to contract; pressure on AV valves which closes to prevent blood moving from ventricle to atria

Question 26

S2 sound

Answer 26

SL valve closure; prevent blood from moving back from the aorta/pulm. trunk

Question 27

isovolumetric contraction

Answer 27

as ventricle contracts, no blood moving anywhere in system, all valves closed, ventricles generate pressure against blood sitting in ventricle, contracts when pressure is greater than the aorta

Question 28

isovolumetric relaxation

Answer 28

pressure dropping within ventricle, all 4 valves closed, AV valve hasn't opened on left side until pressure is low enough for it to open

Question 29

end-diastolic volume

Answer 29

volume left ventricle achieves at end of the diastolic phase

Question 30

end-systolic volume

Answer 30

at the end of the ventricle undergoing systole

Question 31

stroke volume

Answer 31

vol. of blood ejected from the LV or RV into the aorta (or pulm. trunk)

Question 32

what is the formula for stroke volume?

Answer 32

SV = EDV - ESV

Question 33

cardiac output

Answer 33

volume of blood ejected from the LV (or RV) into the aorta/pulm. trunk each min.

Question 34

what is the formula for cardiac output?

Answer 34

CO = HR x SV

Question 35

factors regulating stroke volume

Answer 35

preload, contractility, afterload

Question 36

preload

Answer 36

degree of stretch on the heart before it contracts

Question 37

contractility

Answer 37

forcefulness of contraction of individual ventricular muscle fibers; strength of contraction at any given preload and due to changes in cytosystolic calcium lvls (influx from ECF, release from SR)

Question 38

what increases contractility?

Answer 38

positive inotropic agents

Question 39

what decreases contractility?

Answer 39

negative inotropic agents

Question 40

afterload

Answer 40

pressure ventricles must overcome before SL valves open normal afterload: pressure in aorta approx. 80mmHg, left side of heart needs to generate a lot more pressure before aortic valve opens

Question 41

factors affecting afterload

Answer 41

blood pressure and vessel structure

Question 42

heart rate

Answer 42

bpm, regulated by pacemaker cells in SA node

Question 43

native (resting) HR

Answer 43

75bmp

Question 44

intrinsic HR

Answer 44

100bpm

Question 45

factors regulating heart rate

Answer 45

autonomic regulation, chemical regulation, age, body temp.

Question 46

CV center (medulla oblongata) input

Answer 46

CV center receives input from higher brain regions and from sensory receptors, sends out neural impulses all the time through SNS and PNS (net effect determines if HR goes up or down)

Question 47

SNS effect on heart

Answer 47

via adrenergic receptors on myocardium & pacemaker cells

Question 48

parasympathetic effect on heart

Answer 48

via cholinergic receptors on pacemaker cells