regulation of cardiac function

Question 1

simple factors that govern CO

Answer 1

CO = HR + SV (EDV & ESV)

Question 2

define inotropy

Answer 2

contractility of the myocardium (calcium)

Question 3

define chronotropy

Answer 3

firing rate of SA node (HR)

Question 4

define lusitropy

Answer 4

relaxation of myocardium (Ca2+ removal)

Question 5

what does the inotropic state depend on

Answer 5

• magnitude & rate of Ca2+ release from SR

- affinity of troponin C for Ca2+ (changes with the length of the muscle)

Question 6

what is the effect of sympathetic activation on the cardiac muscle

Answer 6

sympathetic activation increases inotropic state

1. stimulates adrenergic receptors e.g. B1
2. causes phosphorylation of protein e.g. calcium channel
3. causing more Ca2+ to enter cell and be available for contraction

Question 7

phosphorylations leads to

Answer 7

• increased opening of L-type Ca2+ channels
• stimulation of SR and cell memerbane Ca2+ pumps
• faster Ca2+ kineticd
• faster x-bridge cycling

hence more vigorous and more rapid contraction (& relaxation)

Question 8

effect of parasympathetic activation on cardiac muscle

Answer 8

parasympathetic stimulates M2 receptors which:

• inhibits protein kinase A (phosphorylation)
• increases conduction through K channel -> shorter AP duration due to hyperkalaemia

Question 9

difference between skeletal and cardiac muscle force sarcomere length relationship

Answer 9

• no descending limb as CT structure doesn’t allow excessive stretching (passive force curve) stiffness in CM
• steeper ascending limb in cardiac due to actin/myosin overlap & length-dependent sensitivity of troponin-C (more affinity for Ca2+)

Question 10

effects of reduced ATP when cardiac muscle becomes hypoxic e.g. ischemic HD

Answer 10

• reduced Na/K pump
  - hyperkalamia
  - short APD
  - reduced NCX buildup Ca
• reduced myosin head detachment
  - ATP required for relax
• reduced sarcolemmal Ca2+ extrusion
  - increased Ca
• reduced pH
  - impairs coupling and slows conduction
  - H competes with Ca2+ so decreased inotrope

Question 11

deformation during cardiac cycle to pump greater quantities

Answer 11

• circumferential shortening
• longitudinal shortening
• torsion
• transmural shear
• radial wall thickening

Question 12

difference between sympathetic activation on left and right side

Answer 12

• left sided sympathetic nerves mainly go to the ventricles and have a greater effect on contractility. No effect on HR
• right side activates SA node causing increased HR

Question 13

effect of parasympathetic activation on rate, rhythm, and contractility

Answer 13

• reduced HR
• AP duration in atrial myocardium reduced (hyperK)
• deceleration of impulse propagation through AV node
• cardiac vagus stimulation decreases inotropic state of atria

Question 14

what is the main controller of HR

Answer 14

• switching on and off of parasympathetic nervous system (more immediate)

Question 15

what determines oxygen demand

Answer 15

• basal metabolism
• wall force development (geometry and pressure = after load)
• inotropic state
• HR

Question 16

what determines oxygen supply

Answer 16

• perfusion pressure (aortic P and extravascular compression)
• impedance (resistance)
• increase supply by increasing O2 conc, BF, or O2 extraction

Question 17

blood flow equation

Answer 17

change P / R