**Lecture 22

Question 1

Describe the mechanical events of the heart cycle

Answer 1

late diastole = both sets of chambers relaxing
atrial systole = contraction of atria forces additional blood (20%, rest due to passive flow) into ventricles
isovolumic ventricular contraction = pushes AV valve closed, not enough pressure to open semilunar valve
ventricular ejection = pressure exceeds aortic pressure, semilunar valves open and blood ejected
isovolumic ventricular relaxation = ventricular pressure decreases, semilunar valves close
late diastole

Question 2

why do valves open/close

Answer 2

pressure differences, creates heart sounds

Question 3

define stroke volume and cardiac output

Answer 3

amount of blood per beat (EDV-ESV)

amount of blood per minute (HRxSV)

Question 4

Describe the autonomic effect on the SA node

Answer 4

modulation of heart rate (chronotropic) (parasympathetic or sympathetic)
sympathetic = NE on B1 receptor
parasympathetic = Ach on M2 receptor
affects HCN and Ca channel activity, leads to faster/slower depolarization

Question 5

Describe the autonomic effect on ventricular myocytes

Answer 5

modulation of contractility

independent of length

Question 6

how is stroke volume modulated

Answer 6

contraction force, so sarcomere length and contractility of muscle
FRANK STARLING = as EDV increases (decreased HR, increased venous return), sarcomere length increases, so more forceful contraction to account for more blood and prevents buildup
CONTRACTILITY = NE and E act on B1 receptors, activates cAMP messenger system phosphorylates phospholamban and voltage gated Ca channels.
voltage gated Ca channels leads to increased open time, so more Ca entry from ECF, leads to more forceful contraction
Phospholamban (regulatory protein that inhibits SERCA, inhibited by PKA) increases the amount of SERCA, so decreases binding time (shorter duration) and increases amount of cytosol uptake to have more for release (more forceful contraction)