Cardiac Function

Question 1

Define cardiac output (CO)

Answer 1

Heart rate x Stroke vol

Question 2

What occurs in diastole

Answer 2

This is the passive phase during which the heart refills with blood

Question 3

What occurs in systole

Answer 3

This is the active phase during which the heart expels blood

Question 4

What effect does adrenaline have on the heart? How?

Answer 4

Beta1-adrenergic receptors increase the force and rate of contraction and relaxation. GPCR activation increases cAMP. This activates protein kinase A which phosphorylates proteins

Question 5

What effect does the alpha adrenoceptor have on the heart

Answer 5

Shorter action potential. Accelerated relaxation. Prevents Na overload.

Question 6

What controls stroke volume

Answer 6

Stretch (of vessels) and force (of contraction)

Question 7

How is the stretch of blood vessels determined

Answer 7

Skeletal muscle activity
Adrenergic effects on blood vessels (inc or dec)
Respiratory pump (inc/dec depth and frequency)

Question 8

What does inotropic mean

Answer 8

The force of contraction

Question 9

What does lusitropic mean

Answer 9

The force of relaxation

Question 10

What does chronotropic mean

Answer 10

The rate of contraction

Question 11

What are the sites of action of PKA and PKC for hormonal control of cardiac output

Answer 11

NCX (Na/Ca exchanger)
VGCC
RyR (ryanodine receptor)
SERCA channel
Sodium pump
Tn1 (troponin 1)

Question 12

What is the function of voltage gated calcium channels and how are they regulated

Answer 12

Triggers calcium influx/efflux. Accounts for the plateau phase of an action potential
Regulated by:
Activation by depolarisaion. Phosphorylated by protein kinase. Involved in calcium induced calcium release

Question 13

What is the function of ryanodine receptors and how are they regulated

Answer 13

Involved in calcium induced calcium release from the ER.
Regulated by:
pH, Protein kinases, calcium (intra and extra), Stretch/Nitric oxide, binding proteins

Question 14

What is the function of SERCA and how is it regulated

Answer 14

Removes calcium from the cytoplasm (at end of AP) into the ER.
Regulated by Nitric oxide and phospholamban (PLB; reduces affinity for calcium)
PLB can be disinhibited by PKA phosphorylation.

Question 15

What is the function of the NCX and how is it regulated

Answer 15

Triggers calcium influx at the start of an AP; triggers calcium efflux at the end.
Regulated by PKC (enhanced activity; more calcium influx and efflux)

Question 16

What is the function of the sodium pump and how is it regulated

Answer 16

Active transporter. Removes sodium at end of an AP. Maintains ion gradients. Controls membrane potential
Regulated by phospholemman phosphorylation (PKA/PKC)(activates pump)

Question 17

What is the function of the troponin 1 receptor and how is it regulated

Answer 17

Inhibits actin/myosin interaction. (inhibition removed by calcium binding)
Regulated by; PKA phosphorylation - reduces affinity for calcium (reduction in contraction, accelerates relaxation)

Question 18

What is the downstream molecule associated with the beta-adrenoceptor

Answer 18

Protein kinase A

Question 19

What is the downstream molecule associated with the alpha-adrenoceptor

Answer 19

Protein kinase C

Question 20

What is the overall result of activation of either the alpha- or beta- adrenoceptor

Answer 20

Increased stroke vol
Increased ejection fraction
Quicker contraction/AP
More beats per min.