mechanics

Question 1

Frank-Starling mechanism

Answer 1

increased filling/stretching (preload) leads to increased force of contraction, leading to greater stroke volume so cardiac output exactly balances venous return (preload)

Question 2

Starling’s law: 2 influencing factors

Answer 2

changes in number of myofilament cross bridges that interact; changes in Ca2+ sensitivity of myofilaments

Question 3

how do changes in number of myofilament cross bridges that interact affect force of contraction

Answer 3

decreased length → actin filaments overlap → less optimal digitation between thick and thin filaments → fewer cross-bridges → less force in ventricular contraction

Question 4

changes in Ca2+ sensitivity of myofilaments: hypothesis 1 - confromational change explained

Answer 4

based on number of cross bridges: at longer sarcomere length, for same amount of Ca2+ → more force; conformational change of tropinin-C (regulates formation of cross-bridges) → become more sensitive when stretched → less Ca2+ required for same amount of force

Question 5

changes in Ca2+ sensitivity of myofilaments: hypothesis 2 - lattice spacing explained

Answer 5

change in lattice spacing; myofilament stretches → lattice spacing decreases → increase probability of forming stronger cross-bridges

Question 6

define stroke work

Answer 6

work done by heart to eject blood under pressure to arteries

Question 7

calculate stroke work

Answer 7

stroke volume x pressure

Question 8

what is stroke volume influenced by

Answer 8

preload and afterload

Question 9

what is pressure influenced by

Answer 9

cardiac structure