How does the Heart Work? Flashcards
At the _level of the myocyte and myofibri_l what are the 2 key determinants of contractile performance?
- Calcium handling
- Calcium sensitivity
Name at least 3 factors that influence the calcium sensitivity (EC50) of cardiac muscle
- pH
- Temperature
- Caffeine
- Sarcomere Length
- Contractile Protein Phosphorylation
*Changes in these factors typically result in decreased contractile strength/velocity*
What is length-tension relationship as it relates to cardiac muscle?
Further a muscle fiber is stretched increases the strength with which it contracts.
- Think of a rubber band
e.g. - When diastolic volume increases the heart shortens more (yeilding a larger ejection fraction/stroke volume)
Frank-Starling Effects
- What is the effect of increasing preload force on contraction?
Greater the volume of blood entering the heart during diastole (end-diastolic volume) ->
Greater the volume of blood ejected during systolic contraction (stroke volume) and vice versa.
*Due to length-tension relationship – increase the fiber length -> force of contraction for a given stimulus is increased*
What is the role of Troponin I?
- It the inhibitory troponin (hence the “I”)
- Prevents the troponin complex from allowing tropomysin (on the actin) to bind the ATP head of the myosin
- What is an inotrope?
- What is a positive inotrope?
- What is a negative inotrope?
- An inotrope is an agent that alters the force or energy of muscular contractions.
- Positive: increase the strength of muscular contraction
- Negative: weaken the force of muscular contractions
List the 6 major responses of the heart muscle to beta adrenergic stimulation
- Phosphorylation of Ca channels in the SA node cells
- Phosphorylation of Ca channels in ventricular cells
- Phosphyrylation of Na pump
- Phosphorylation of Phospholamban
- Phosphorylation of FKB
- Phosphorylation of Troponin I
What is the effects of phosphorylating the calcium channels of the SA node cells?
Increased Heart Rate (HR) -> improved cardiac output (co)
- CO = HR x SV (stroke volume)
What is the effect of phosphorylation of calcium channels in ventricular cells?
- Increased calcium entry into the cell
- Increased force contraction
- Leads to imprved ejection fraction (EF)
- Otherwise known as (+) inotropy
- Leads to imprved ejection fraction (EF)
What are the effects of phosphorylating the Na pump in cardiac cells?
- Increases Ca efflux (via Na-Ca exchange)
- Leads to Enhanced relaxation and diastolic filling
What are the effects of phosphorylating phospholamban?
- Disinhibition of SR calcium pump (SERCA2)
-
Increased SR calcium load
- Leads to improved diastolic filling
What is the effect of phosphorylating FKB?
- Enhances Ryr receptor mediated calcium release
- Leads to enhanced contractility
What is the effect of phosphorylating of Troponin I?
- Decreases CA affinity for Troponon C (C for calcium)
- Leads to enhanced relaxation
What accomodations does our heart make when we wake up/get out of bed?
Postural accomodation
- Venous pump via skeletal musculature
- Increased venous return
- Increased EDV (end diastolic volume aka pre-load)
- Increased SV (stroke volume)
- Increased EDV (end diastolic volume aka pre-load)
- Increased venous return
What physiologic changes occur during isotonic execises as it relates to the heart?
(Isotonic excercise - jogging, non resistance excercise)
Decreased peripheral vascular resistance
- Increased vnous return (Frank-Starling relationships)
- Increase heart rate
- Increase inotropy
- Increase heart rate
