Cardiovascular Mechanics Flashcards
All muscle cells when isolated can contract on their own. TRUE or FALSE and explain answer
False - Cardiac muscle needs an influx of calcium to contract
When does contraction happen relative to Calcium influx
Contraction happens after calcium influx
Calcium is released from sarcoplasmic reticulum after the ryanodine receptors are activated and then binds to troponin to move tropomyosin which exposes the myosin binding filaments on the actin
To what part of the microfiliament are the T tubules aligned with
Suggest why?
The Z line
Describe how calcium is moved around within the cardiac muscle cell
Enters via channels in T tubules called LT calcium channels
some of the calcium attaches directly to the troponin, but most acts on ryanodine to open the calcium Chanel in the sarcoplasmic reticulum which increases the amount of calcium which binds to troponin
Some of the calcium is taken back into the sarcoplasmic reticulum by active transport
Some of it is pumped back out by the T tubule using Na/Ca co transporter
What’s the main job of T tubules
To carry surface depolarisation deep into the cell
What are the dimensions of a ventricular cell
About 100 micrometers long and 15 micrometers wide
What are the dimensions of T tubules
200nm in
How far apart are T tubules spaced
2 micrometers apart
What happens to calcium in the steady state
There is no net gain/loss of calcium due to:
Loss of calcium from the sarcoplasmic by the SR calcium ATPase
AND loss of calcium by Na/Ca exchanger
What is the name of the channel that allows Calcium to enter the sarcoplasm from the T tubule
L type Calcium channel
What’s another name for ryanodine
SR Calcium Channel
How can you change the amount of calcium in the sarcoplasm
Sympathetic stimulation
Phosphorylation of certain proteins
Draw a diagram of the relationship between force and calcium concentration in the cell
S shaped up to about 100 milimoles
Describe the tension length experiment in cardiac muscles and draw diagram
As muscle length increases, so does the force it can bear
Passive force ( the ‘recoil’) always increases but the active force decreases after a certain point
1)Draw force (% max) vs muscle length (% max) of cardiac muscle showing:
Total force
Active force
Passive force
2) Which part of this is clinically relevant
1) Total force increases to a max just before 100% of stretching length and then decreases and plateaux
Active force increases to a max just before 100% and continuously goes down to nearly 0 after 200%
Passive force continually goes up
2) Only relevant up to 100%
What are the 2 forms of contraction that the heart muscles undergo
And give examples
Isometric - muscle fibres stay the same length but pressure increases in both ventricles eg ventricles filling up with blood
Isotonic - muscle fibre shortens and ejects blood out of the ventricle eg ventricles contracting to push blood into aorta
What’s preload
Weight that stretches muscle before it is stimulated to contract
What is after load
Weight not apparent to muscle in resting state
Only when muscle has started to contract is it encountered
What correlations of preload and after load are clinically important
Preload = filling up of ventricles
After load = contraction of ventricles
Draw a graph of force vs preload (stretch) for an isometric muscle
Curved and increases to a point then in a curve decreases
Draw graph of shortening vs after load for an isotonic contraction for both with a smaller preload(blue) and a larger preload(green )
Straight line to 0 but the one with a larger preload has a higher line
What correlates to preload
Stretching of ventricles as it fills with blood
So the venous drainage into the entry lees dtermines the preload
State the Franklin Starling relationship diastolic
Increased fibre length increases ventricular constriction
Give 2 reasons for the Franklin Starling relationship
1) As it stretches the actin gets further and further apart, the actin is further away from each other so can bind to more myosin
(At shorter lengths the actin is closer to each other and so sub optionally binds to myosin as they are in each other’s way )
2) Troponin C undergoes a conformational change to bind more favourably to calcium when it is stretched
3) stronger cross bridges between myosin and actin when further away
What is the definition of stroke work
Work done by ventricles under pressure to pump blood into aorta and pulmonary artery
Stroke work = Volume of blood pumped * pressure
What is the law of La Place
When the pressure on a wall is held the same, the tension on its walls increases with increasing radius
T = R*P
Tension = readius* pressure
apply the law of LaPlace to the structure of the heart
Tension = Pressure *radius
You want a higher pressure in the aorta than the pulmonary artery
BUT….
You want the tension to be the same (as you want the Heart muscles to use the same force)
So the left ventricle has a smaller radius than the righ ventricle
