Mechanics 1 Flashcards

Question

What is eccentric?

Answer 1

lengthening

Answer 2

preload enhances contractile force (increase in contractile energy with stretch = Starling's Law) stretch is set by the diastolic ventricular filling pressure (diastole determines the preload) filling of ventricles with blood causes stretching and generates isometric contraction

Answer 3

afterload impairs shortening | an increase in afterload causes the rate and degree of shortening to decrease

Answer 4

shortens the muscle more as the cardiac cells compensate for the greater volume of blood

Answer 5

Diastole the walls stretch as blood fills the ventricles and pressure increases --> stretch determines preload --> preload dependent on VENOUS RETURN TO THE HEART

Answer 6

end diastolic volume end diastolic pressure right atrial pressure

Answer 7

Afterload is the force the heart must over come to eject blood from the ventricles

Answer 8

diastolic arterial BP must be overcome by pressure in ventricles for blood to be ejected

Answer 9

they have an increased afterload increase BP increased risk of high pressure in heart

Answer 10

increased diastolic fibre length increases ventricular contraction increased stretching/preload increases speed of shortening

Answer 11

it reduces interference by myosin heads that are pulling in the wrong direction beyond the sarcomere midpoint

Answer 12

larger preload means ventricles need to increase SV to ensure CO balances venous return The law means that the heart can adapt to changes in preload (venous return)

Answer 13

Changes in number of myofilament crossbridges that interact - at shorter lengths actin filaments overlap - reduced number of myosin crossbridges that can be made because some are pulling in the opposite direction to majority which reduces net tension generated But this is also the case in skeletal muscle so which is cardiac muscle more sensitive than skeletal? FACTOR 2

Answer 14

Increased Ca sensitivity with increased length At physiological [Ca] lower active tension as only fraction of crossbridges are activated - force increases more steeply with stretch

Answer 15

1. Troponin C (TnC) is a thin filament binding to Ca and regulate cross bridge formation - longer sarcomere increases TnC affinity for Ca - conformational protein change - less Ca needed for same force 2. Stretch causes lattice spacing (space between A and M filaments ) to decrease - increase chance of forming strong cross bridges - and so more force is produced for same amount of Ca

Answer 16

a sudden increase in afterload on the heart causes an increase in ventricular inotropy if stretch is maintained there is a further slow increase in force over 5 minutes due to increased Ca transients (slow force response)

Answer 17

= work done by heart to eject blood under pressure into aorta and pulmonary artery

Answer 18

SV x Pressure preload and afterload influence SV cardiac structure influences the pressure at which blood is ejected

Answer 19

when pressure in a cylinder is constant, tension in walls increases with radius T (wall tension) = P (pressure in vessel) x R (radius) /h tension is constant h takes into account wall thickness

Answer 20

ventricles and blood vessels

Answer 21

wall tension kept same between L and R ventricle despite higher pressure in LV - radius of curvature of LC less than RV so higher pressures generated with similar wall tension - heart does not rip despite high pressures generated

Answer 22

wall stress kept low by long narrow thin walled ventricle and a small radius to allow for a high pressure

Answer 23

pressures are lower so ventricles are spherical to give a larger radius

Answer 24

dilated cardiomyopathy enlarged radius increase wall stress bad --> aneurysm