Inotropy Flashcards
Explain how cardiac contractility is regulated by changes in intracellular calcium Describe the mechanisms through which the sympathetic nervous system modifies contractility Briefly explain why structural adaptation of the myocardium to changing loads is beneficial in the short term but detrimental in the long term
Inotropy relates to what?
The factors that affect the force of muscle contraction
What receptor allows for the movement of calcium in cardiac muscle?
Ryanodine receptor 2
Name thevoltage sensitive receptor involve in the movement of calcium in cardiac muscle
Voltage sensitive dihydropyridine receptor channel
What ions are responsible for the relaxation of cardiac muscle?
Calcium moving out while sodium moves in 3:1
What is meant by positive inotropism?
Cardiac muscle has graded responses in terms of the force of contraction.
These depend of intracellular calcium ion concentration.
As the concentration of calcium increases the force of contraction also increases…this is positive inotropism
Why can a increase in calcium ion concentration allow for a greater force of contraction?
Troponin is responsible for the formation of cross bridges that allow for contraction. Troponin is capable of binding up to four calcium ions per molecule and therefore as the concentration of calcium increases more cross bridges are formed
What 3 effects does sympathetic nervous system have on the heart (as positive inotropes)?
Phosphorylation of slow calcium channels; allowing for the conduction of more calcium
Sensitisation of troponin to calcium; lower affinity for binding
Stimulation of calcium uptake into the sarcoplasmic reticulum; allows cardiac muscle to relax faster
Acetylocholine is a negative inotrope as it only works on what chambers?
Atria
Name three means of altering the force of contraction with cardiac muscle
Alter the length-tension relationship of the heart muscle (preload)
Change the cytosolic free calcium concentration
Change the sensitivity of the myocardial contractile proteins to calcium
What are the results of a increase in contractile strength of the ventricles?
Able to handle a greater preload (greater filling volume)
Ability to empty more completely
Ability to do all this against an increased afterload (increased aortic pressure)
To deliver an increased stroke volume (even when increased heart rate reduces the time available for ventricular filling)
How much of the cardiac output goes to supply the coronary circulation?
4-5%
How does oxygen supply influence contractility?
Contraction weakens if the supply is decreased by deficient respiration, decreased arterial pressure or decreased coronary blood flow
How does an excess of potassium influence contractility?
This causes cells to hyperpolarise, resulting in a weakened contraction. Also acts to block the conducting system and therefore slow the heart rate.
Cardiac muscle becomes flaccid and dilated
When would you be likely to see eccentric hypertrophy?
During volume overload
When would you be likely to see concentric hypertrophy?
During pressure overload
