mechanics 1

Question 1

size of ventricular cells

Answer 1

100micrometers long

and 15 micrometers wide

Question 2

t-tubule openings up to ? in diameter

Answer 2

200nm

Question 3

how far apart are t-tubules spaced?

Answer 3

2 micrometers

spaced so that a T-tubule lies across each Z-line of every myofibril

Question 4

Cardiac heart will not beat without

Answer 4

external calcium

Question 5

what is SERCA and what does it do?

Answer 5

sarco/endoplasmic reticulum calcium ATPase

some of the calcium is taken back up into the SR

Question 6

why is the cardiac muscle more resistant to stretch?

Answer 6

due to the properties of its extracellular matrix and cytoskeleton

• hence exerts more passive force so it much more resilient to stretch
• less compliant than skeletal muscle

Question 7

what is passive force based on?

Answer 7

resistance to stretch of the muscle

Question 8

why is the ascending limb only of use and not the descending in the length-tension curve?

Answer 8

descending limb doesn’t happen in physiological conditions because pericardium restricts the stretching

Question 9

preload is dependant on

Answer 9

the venous return

Question 10

measures of preload

Answer 10

EDV
EDP
Right atrial pressure

Question 11

what is afterload

Answer 11

load against which the left ventricle ejects blood after opening of the aortic valve

any increase in afterload decreases the amount of isotonic shortening that occurs and decreases the velocity of shortening

Question 12

more preload =

Answer 12

more force

Question 13

frank starling relationship

1) cross bridge theory

Answer 13

1) Changes in the number of myofilament cross-bridges:
§ At shorter lengths than optimal, the actin filaments overlap thus reducing the number of myosin cross-bridges that can be made.

Question 14

2 hypothesis for the calcium sensitivity theory

Answer 14

1. Troponin C (TnC) is a thin filament that binds to calcium and regulates cross-bridge formation.
   a. At longer sarcomere lengths, the affinity of troponin C for calcium could be increased due to a conformational change in TnC.
   b. Less calcium is required for same force generated.
2. With stretch, the space between (lattice spacing) myosin and actin filaments DECREASES.
   a. With decreasing myofilament lattice spacing, the probability of forming strong cross-bridges increases.
   b. This produces more force for the same amount of calcium.

Question 15

define stroke work and it’s equation

Answer 15

Stroke work = the work done by the heart to eject blood under pressure into the aorta and pulmonary artery (in one contraction).
defined by the equation on the left; work = SV x P.
§ Stroke Volume (SV) is affected by: preload & afterload.
§ Pressure (P) is affected by the structure of the heart.

Question 16

how does the shape of the left ventricle vary from the right?

Answer 16

The radius of curvature of the walls of the LEFT ventricle is less of that of the RIGHT ventricle.
o This allows the LV to generate high pressures with similar wall tension as T = PR.