Cardiac cycle Flashcards
Define cardiac output (CO)
Heart rate x Stroke vol
What occurs in diastole
This is the passive phase during which the heart refills with blood
What occurs in systole
This is the active phase during which the heart expels blood
What effect does adrenaline have on the heart? How?
Beta1-adrenergic receptors increase the force and rate of contraction and relaxation. GPCR activation increases cAMP. This activates protein kinase A which phosphorylates proteins
What effect does the alpha adrenoceptor have on the heart
Shorter action potential. Accelerated relaxation. Prevents Na overload.
What controls stroke volume
Stretch (of vessels) and force (of contraction)
How is the stretch of blood vessels determined
Skeletal muscle activityAdrenergic effects on blood vessels (inc or dec)Respiratory pump (inc/dec depth and frequency)
What does inotropic mean
The force of contraction
What does lusitropic mean
The force of relaxation
What does chronotropic mean
The rate of contraction
What are the sites of action of PKA and PKC for hormonal control of cardiac output
NCX (Na/Ca exchanger)VGCCRyR (ryanodine receptor)SERCA channelSodium pumpTn1 (troponin 1)
What is the function of voltage gated calcium channels and how are they regulated
Triggers calcium influx/efflux. Accounts for the plateau phase of an action potentialRegulated by:Activation by depolarisaion. Phosphorylated by protein kinase. Involved in calcium induced calcium release
What is the function of ryanodine receptors and how are they regulated
Involved in calcium induced calcium release from the ER.Regulated by:pH, Protein kinases, calcium (intra and extra), Stretch/Nitric oxide, binding proteins
What is the function of SERCA and how is it regulated
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.
What is the function of the NCX and how is it regulated
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)
What is the function of the sodium pump and how is it regulated
Active transporter. Removes sodium at end of an AP. Maintains ion gradients. Controls membrane potentialRegulated by phospholemman phosphorylation (PKA/PKC)(activates pump)
What is the function of the troponin 1 receptor and how is it regulated
Inhibits actin/myosin interaction. (inhibition removed by calcium binding)Regulated by; PKA phosphorylation - reduces affinity for calcium (reduction in contraction, accelerates relaxation)
What is the downstream molecule associated with the beta-adrenoceptor
Protein kinase A
What is the downstream molecule associated with the alpha-adrenoceptor
Protein kinase C
What is the overall result of activation of either the alpha- or beta- adrenoceptor
Increased stroke volIncreased ejection fractionQuicker contraction/APMore beats per min.
