Cardiac muscle and cardiac output

Question 1

What is the contractile unit in myocardial cell?

Answer 1

sarcomere

Question 2

what is the length of the sarcomere

Answer 2

from Z line to Z line

Question 3

what does sarcomere contain?

Answer 3

thick filaments (myosin) and thin filaments (actin, troponin, tropomyosin)

Question 4

how is cardiac muscle contract?

Answer 4

thin filaments slide along thick filaments by forming and breaking cross bridges between actin and myosin

Question 5

what are intercalated disks

Answer 5

ends of the cells

Question 6

fxn of intercalated disks

Answer 6

maintain cell-cell adhesion

Question 7

fxn of gap junctions

Answer 7

low restance path btwn cells for rapid electical spread of AP

Question 8

because of gap junctions, heart behaves as an ___

Answer 8

electrical syncytium

Question 9

more mitochondria in cardiac or skeletal muscle?

Answer 9

cardiac

Question 10

what are T tubules

Answer 10

invaginate cells of Z lines

carry AP into cell interior

Question 11

Are T tubules more developed in ventricles or atria

Answer 11

ventricles

Question 12

What is the SR

Answer 12

storage and release of Ca2+ for EC coupling

Question 13

Steps in EC coupling

Answer 13

Page 77

Question 14

What is contractability/inotropy?

Answer 14

intrinsic ability of cardiac muscle to develop force at a given muscle length

Question 15

____ is the intrinsic ability of cardiac muscle to develop force at a given muscle length

Answer 15

contractability/inotrophy

Question 16

Contractability/inotropy can be estimated by the ____

Answer 16

Ejection fraction

Question 17

equation for ejection fraction

Answer 17

EF = stroke volume/ end diastolic volume

Question 18

How does heart rate affect contractility

Answer 18

More AP per unit time –>
more Ca2+ enter myocardial during AP plateaus –>
more Ca2+ in SR and released from SR
more tension produced during contraction

Question 19

What is a positive staircase

Answer 19

Incr HR, incr force of contraction in stepwise as intracellular [Ca2+] incr cumulatively

Question 20

What is postextrasystolic potentiation?

Answer 20

beat after an extrasystolic beat has incr force of contraction

extra Ca2+ enter cells during extrasystole

Question 21

how does sympathetic stimulation (catecholamines via B1 receptors) affect contractility

Answer 21

incr inward Ca2+ current during plateau of cardiac AP,
incr activity of Ca2+ pump of SR
more Ca2+ in SR
more Ca2+ available for release

Question 22

How does cardiac glycosides (digitalis) affect contractility

Answer 22

incr force of contraction by inhibit Na+/K+ ATPase in membrane
incr intracellular Na+, decr Na+ gradient
decr Na+ Ca2+ exchange, so more Ca2+ inside cell

Question 23

How does parasympathetic stimulation (ACh via muscarinic receptors) affect contractility

Answer 23

decr inward Ca2+ current during plateau

decr force of contraction in atria

Question 24

___ is the end-diastolic volume = Right atrial pressure

Answer 24

Preload

Question 25

Preload is the ___

Answer 25

EDV = Right atrial pressure

Question 26

When venous return incr, end diastolic volume ____ and stretches the ventricular muscle fibers

Answer 26

increases

Question 27

When venous return incr, end diastolic volume increases and _____ the ventricular muscle fibers

Answer 27

stretches

Question 28

____ for the LV is the aortic pressure

Answer 28

Afterload

Question 29

Afterload for the LV is the ___

Answer 29

aortic pressure

Question 30

Increases in aortic pressure cause ___ in afterload on the LV

Answer 30

increase

Question 31

____ for the RV is pulmonary artery pressure

Answer 31

Afterload

Question 32

Afterload for the RV is ____

Answer 32

pulmonary artery pressure

Question 33

Sarcomere length determines the ____

Answer 33

max # of cross bridges between actin and myosin

Question 34

Sarcomere length determines ____

Answer 34

the max tension or force of contraction

Question 35

When is velocity of contraction (at a fixed muscle length) MAX?

Answer 35

when afterload = 0

Question 36

Decr in velocity of contraction, ____ in afterload

Answer 36

increases

Question 37

Frank Starling relationship

Answer 37

describes incr in SV and CO in response to incr in venous return or EDV

Question 38

Frank Starling relationship is based on ____ relationship. Why?

Answer 38

length-tension relationship in the ventricle incr in EDV, incr ventricular fiber length, incr tension

Question 39

What is the mechanism that matches CO to venous return

Answer 39

Frank starling relationship, greater venous return, greater CO

Question 40

Incr in contractility shift Frank Starling curve ____

Answer 40

shift upward, increasing CO for any RA pressure or EDV

Question 41

Diastolic/systolic pressure Curve is the relationship between ____

Answer 41

diastolic/systolic pressure and diastolic/systolic volume in the ventricle

Question 42

LV cycle loop | 1--> 2 (isovolumetric contraction)

Answer 42

1) LA fills LV with blood (~140 mL= EDV) low LV pressure because muscle is relaxed 2) on excitation, LV contracts and ventricular pressure incr Mitral valve closes (LV pressure > LA pressure) Since no blood ejected from ventricle= isovolumetric

Question 43

LV cycle loop | 2--> 3 (ventricular ejection)

Answer 43

3) Aortic valve opens when LV pressure > aortic pressure blood eject into aorta and LV volume decr --> STROKE VOLUME (LV ejected) 4) volume leftover in LV = end systolic volume

Question 44

How do you measure stroke volume

Answer 44

width of the Pressure volume loop

Question 45

LV cycle loop | 3 --> 4 (isovolumetric relaxation)

Answer 45

5) LV relaxes Aortic valve closes because LV pressure < aortic pressure 6) since all valves closed, LV volume constant

Question 46

LV cycle loop | 4--> 1 (ventricular filling)

Answer 46

7) when LV pressure < LA pressure, mitral valve opens and LV fills 8) LV fills to 140 mL (end-diastolic volume)

Question 47

Changes in LV cycle loop | Increased preload

Answer 47

INCR WIDTH OF P-V LOOP Increased EDV (incr venous return b/c incr blood volume or decr venous capacitance) incr Stroke volume (more blood ejected from LV)

Question 48

Changes in LV cycle loop | Increased afterload

Answer 48

DECR WIDTH OF P-V LOOP due to increased aortic pressure so LV ejecting blood against higher P --> decr in stroke volume increased end-systolic volume

Question 49

Changes in LV cycle loop | Increased contractility

Answer 49

LV has greater tension during systole incr stroke volume decrease in end-systolic volume