Topic 2 Flashcards
To maintain homeostasis, blood must flow across a resistance propelled by –
pressure developed by the heart
describe pressure of large valves
low pressure
describe the size of in flow valves (AV valves)
large
examples of small outflow valves
pulmonary and aortic semilunar valves
describe a result of the varying fiber orientation from endocardium to epicardium
small sarcomere shortening –> large changes in chamber volume
Name one way the fiber orientations of muscle layers improve efficiency of pumping action
heart chamber needs to twist and rotate to squeeze out blood
Where is the blood supply to the heart?
coronary arteries on epicardium
What % of the body is the energy demand of the heart?
10
The heart produces ATP and is 60-90% – with no stored reserves
fatty acid beta oxidative
function of working cells
contract in ventricles and atria
function of pacemaker cells
spontaneously depolarizing cells that initiate AP in SA and AV nodal cells
function of conducting cells
conduct AP at specific rates to specified regions of working cells
how are myocytes physically connected?
intercalated disks
how are myocytes electrically connected?
gap junctions
what is total force?
force measured at isometric contraction peak
what is active force?
force generated by cross-bridges (total-passive)
what is passive force?
force measured when muscle is at rest
In addition to the ECM, what is the primary source of resting tension?
titin
Which striated muscle is stiffer?
cardiac
Where are Length-tension curves are derived from?
multiple isometric twitch contractions (at diff lengths)
What sarcomere length range does maximal active force occur?
2-2.2 micrometer
Preload
load that stresses a resting muscle before it is stimulated
afterload
load encountered after muscle is stimulated and starts to contract
what does the velocity of muscle shortening depend on?
load
light load = – velocity
fast
most muscle contractions are –
afterloaded isotonic contractions
what can be directly measured from the heart and circulation to gauge its function?
stress, velocity, work
stress =
force/area
what is the common stress of heart?
2-4 kg/cm^2
velocity =
length/time
work =
force x length
blood pressure determines –
afterload
Why is the LV wall thicker than the RV wall?
Thicker wall to meet pressure demands (4x P)
persistent higher pressure –>
higher wall tension
pressure =
force/tension
Law of Laplace correlates mechanical info from hear wall (cells) to –
chamber pressures and volumes
