Cardiac Muscle Flashcards
(24 cards)
Why is the heart’s contraction labelled as Persitaltic
Because it functions by a squeezing action
What do capillary muscles of the heart support with
Support with opening and closing the mitral valve
What percentage of blood is expelled from a healthy chamber/heart with each beat
Around 70%
What are the two methods by which heart function is increased
Inotropy - Increased force of contraction (Increases Stroke Volume)
Chronotropy - Increased frequency of contraction (Increases HR)
Compare the direction of heart fibres on the outside to those on the inside
Those on the inside are more vertical than those on the outside which are more transverse (to allow wringing action)
What causes the wave of depolarisation across the heart
Electrical impulses from the nodes that cause simultaneous pumps in both sides of the heart
Does each cardiomyocyte have its own AP
Yes - generated by Nodes
How is the action potential propagated into cardiomyocytes
Along the sarcolemma into the T-Tubules
Tetanus
Sustained Muscle Contraction
Seen in SkM NOT Cardiac Muscle
Qualitatively compare the length of the cardiac vs skeletal muscle action potential
The cardiac action potential is much longer to avoid tetanus in cardiac muscle
(About 4ms vs 400ms)
Qualitatively describe the amount of Ca2+ actually enters a cell in cardiomyocyte contraction
Very Small Amount is actually needed
Qualitatively describe the amount of Ca2+ actually enters a cell in cardiomyocyte contraction
Very Small Amount
What causes the plateau in cardiac muscle action potential
Caused by an Influx of Ca2+ ions from the extracellular space moving into the cytosol
This is as a result of the opening of L-type (long opening) Ca2+ channels which open more slowly than the Na+ channels responsible for the initial phase of the impulse, leading to a delayed repolarisation of the sarcolemma
Diad
Structure formed by L-type Ca2+ channels in T-Tubules, Ryanodine Receptors and the significant store of Ca2+ wihin a muscle cell
What does the release of Ca2+ from T-Tubules cause in cardiac muscle
Release of Ca2+ from intracellular stores of muscle cells which cause myosin actin interaction (causes 75-90% of cardiac muscle contraction)
What does the action potential travelling along the sarcolemma cause
An influx of Ca2+ which directly causes muscle contraction (causes 10-25% of cardiac muscle contraction)
Effect of diastolic length on Cardiomyocyte sensitivity to Ca2+
Positive correlation
How does caffeine affect cardiac muscles
It is a positive Inotrope that acts on Ca2+ release channels of the sarcoplasmic reticulum
How do L-type Ca2+ blockers work (give an example of a drug name)
They are negative inotropes that may be beneficial in angina as reduced contraction reduces energy demand, which reduces ischaemia and thus chest pain
e.g. Verapamil
How does digitalis (with careful controlled dosage) help treat congestive heart failure
It enhances Ca2+ release which increases cardiac contractility, improving heart function
**Digoxin is modern digitalis
Which substances does the heart get its ATP from (Ratios)
70% ATP from fat oxidation
20% ATP from glucose oxidation
10% ATP from other sources like glycolysis
LOTS of O2 needed and has many many mitochondria
What happens if the cardiac afterload is increased (Increased resistance of heart LV)
Cardiac muscles strengthen and causes compensated hypertrophy; can lead to De-compensation that causes heart failure where hypertrophy stops and the heart becomes baggier, decreasing the ejection fraction of blood
Why is an ischaemic event of the heart so bad
Due to the very high metabolic demand of cardiac tissue
Are there a lot of mitochondria in cardiac muscle
Yes tons
