force generation by the heart

Question 1

how is striation achieved

Answer 1

regular arrangement of contractile protein

Question 2

what is missing in cardiac muscle

Answer 2

neuromuscular junctions

Question 3

cardiac myocytes are electrically coupled by

Answer 3

gap junctions

Question 4

what are gap junctions

Answer 4

protein channels which forms low resistance electrical communication pathways between neighbouring myocytes

Question 5

what do gap junctions do

Answer 5

they ensure that each electrical excitation has reaches all the cardiac myocytes

Question 6

what do desmosomes do

Answer 6

provide mechanical adhesion between cardiac cells

Question 7

what are myofibrils

Answer 7

contractile units of muscle

Question 8

within myofibrils, the actin and myocin is arranged into

Answer 8

sarcomeres

Question 9

what does force generation depend upon

Answer 9

ATP dependent interaction between myosin and actin

Question 10

ATP is required for both

Answer 10

contraction and relaxation

Question 11

Ca++ is required for

Answer 11

cross bridge formation

Question 12

actin potential switches on

Answer 12

cardiac muscle contraction

Question 13

Ca++ is released from

Answer 13

sarcoplasmic reticulum

Question 14

in cardiac muscle, the release of Ca++ from SR is dependent on

Answer 14

the presence of extracellular Ca++

Question 15

diastole

Answer 15

ventricular muscle relaxes

Question 16

systole

Answer 16

ventricular muscle contracts

Question 17

when muscle fiber is relaxed

Answer 17

no cross bridge binding because the cross bridge binding site on actin is physically covered by the troponintropomyosin complex

Question 18

binding of actin and myosin cross bridge

Answer 18

triggers power strokes that pulls thin filament inward during contraction

Question 19

when muscle fiber is excited

Answer 19

Ca++ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross bridge binding site
cross bridge binding occurs

Question 20

long refractory period prevents

Answer 20

generation of tetanic contraction

Question 21

refractory period

Answer 21

a period following an action potential in which it is not possible to produce another action potential

Question 22

during the plateau phase of ventricular action potential the Na+ channels are

Answer 22

in depolarised closed state

ie sodium channels closed

Question 23

during the descending phase of action potential

Answer 23

the K+ channels are open and the membrane can not be depolarised

Question 24

the long refractory period is protective for the heart as

Answer 24

it prevents generation of tetanic contractions

Question 25

contraaction of ventricular muscle

Answer 25

ejects the stroke volume

Question 26

stroke volume

Answer 26

the volume of blood ejected by EACH ventricle PER heartbeat

Question 27

SV =

Answer 27

end diastolic volume - end systolic volume

Question 28

how is the stroke volume regulated

Answer 28

intrinsic and extrinsic mechanisms

Question 29

intrinsic

Answer 29

within heart

Question 30

extrinsic

Answer 30

hormonal and nervous control

Question 31

changes in stroke volume are brought about by

Answer 31

changes in the diastolic length/diastolic stretch of myocardial fibers

Question 32

the diastolic length and stretch is determined by

Answer 32

the volume of blood within each ventricle at the end of diastole. this is caked END DIASTOLIC VOLUME

Question 33

the end diastolic volume determines

Answer 33

the cardiac preload (the diastolic length/stretch of myocardial fibers)

Question 34

the end diastolic volume is determined by

Answer 34

the venous return to the heart

Question 35

the frank starling curve describes

Answer 35

the relationship between venous return, end diastolic volume and stroke volume

Question 36

the more the ventricle is filled with blood during diastole

Answer 36

the greater the volume of ejected blood will be during the resulting systolic contraction (stroke volume)

Question 37

stretch also increases the affinity of troponin for

Answer 37

Ca++

Question 38

optimal length in cardiac muscle is achieved by

Answer 38

stretching the cardiac muscle

Question 39

if venous return to right atrium increases

Answer 39

EDV of right ventricle increases

Question 40

starling law leads to

Answer 40

increased SV into pulmonary artery

Question 41

venous return to left atrium from pulmonary vein increases

Answer 41

EDV of left ventricle increases

Question 42

starlings law leads to

Answer 42

increased SV into aorta

Question 43

afterload means the

Answer 43

resistance into which heart is pumping

Question 44

the extra load is imposed

Answer 44

after the heart has contracted

Question 45

if afterload increases, at first

Answer 45

heart unable to eject full SV, so EDV increases

Question 46

force of contraction rises by

Answer 46

frank- stark mechanism

Question 47

if increased afterload continue to exist, eg, untreated hypertension eventually the

Answer 47

ventricular muscle mass increases (ventricular hyertrophy) to overcome resisitance

Question 48

extrinsic control of stroke volume involves

Answer 48

nerves and hormones

Question 49

the ventricular muscle is supplied by

Answer 49

sympathetic nerve fibers

Question 50

the neuro transmitter in extrinsic control is

Answer 50

noradrenaline

Question 51

stimulation of sympathetic nerves

Answer 51

increases the force of contraction

Question 52

this is known as

Answer 52

positive inotropic effect

Question 53

stimulation of sympathetic nerves also causes

Answer 53

positive chronotropic effect

Question 54

force of contraction increases

Answer 54

greater Ca++ influx

Question 55

the effect is ____ mediated

Answer 55

cAMP

Question 56

the peak ventricular pressure

Answer 56

rises

Question 57

rate of pressire change during systole

Answer 57

increases

Question 58

this reduces the duration of

Answer 58

systole

Question 59

rate of ventricular relaxation

Answer 59

increases (increased rate of Ca++)

Question 60

this reduces the duration of

Answer 60

diastole

Question 61

peak ventricular pressure rises

Answer 61

contractility of heart at a given EDV rises

Question 62

parasympathetic nerves have

Answer 62

no direct effect on SV

Question 63

vagal stimulation (parasympathetic) has major influence on

Answer 63

rate, not force of contraction

Question 64

adrenaline and noradrenaline released from adrenal medulla have

Answer 64

inotropic and chronotropic effect

Question 65

cardiac output

Answer 65

the volume of blood pumped by EACH ventricle per MINUTE

Question 66

CO =

Answer 66

SV x HR

Question 67

the resting CO in a healthy adult is approcx

Answer 67

5 litres per minute

Question 68

how to regulate the CO

Answer 68

regulate stroke volume and heart rate