Cardiovascular Mechanics Flashcards
What is excitation contraction coupling
Electrical event/AP leads to calcium influx and release (calcium transient) , which is followed by the contractile event.
The electrical event and the contractile event are coupled
What external ion is cardiac muscle depend on for contraction
Calcium
__ __________ are the finger like invaginations on ventricular cells that lie alongside each __ line of every myofibril. ________ __________ is the lace like structure that lies above the myofilaments
T(ransverse) tubules
z
Sarcoplasmic reticulum
What channels are found in T tubules
LTC CC ( L type calcium channel) Close to RyR (Ryanidine receptors/ SR calcium release channel)
How is muscle contraction brought about
L type Ca channel opens in response to change in voltage
Ca enters cytosol
Binds to SR Ca release channels(ryanodine recep) (ligand operated)
Calcium stored in SR released into cytosol
Ca binds to troponin in myofilaments and causes contraction
How is muscle relaxation brought about
Ca pumped back up against conc grad by SR Ca ATPase
Active transport back into SR for release at next beat
Ca that entered cell effluxed via Na Ca exchanger during diastole
What happens during the diastolic period
Same amount of calcium that entered cell to trigger contraction is effluxed via the Na Ca exchanger in the T tubule membrane.
Uses downhill energy gradient of sodium moving into cell to supply necessary energy to expel calcium from cell
Cardiac muscle is in calcium balance
Describe the length tension relation in cardiac muscles
As we increase muscle length, we increase the force of production
Both baseline force and max force increase (passive and active force)
Relates to ISOMETRIC FORCE
What is active force vs passive force
Active force caused by cross bridges
Passive force caused by elasticity of cardiac cells; when stretched, they recoil a bit
Compare the elasticity of skeletal and cardiac muscle, and the consequences of this in terms of length tension relation
Cardiac muscle is more resistant to stretch and less compliant than skeletal, due to properties of extra cellular matrix and cytoskeleton
Therefore can generate more passive force as muscle length increases
If you keep stretching cardiac tissue, will force keep increasing? Why?
No
Force falls when length passes optimum
Cardiac cells only work on ascending limb of length tension graph; cannot overstretch cardiac tissue
Heart contained in pericardial sac, can only stretch a certain amount
Where and when do isometric and isotonic contraction occur in the heart
Isometric- muscle fibres don’t change length but pressures increase in both ventricles
Isotonic- shortening of fibres and blood is ejected from ventricles
When pressure in ventricles overcomes back pressure in aorta, blood expelled, ventricular cells shorten, eject blood out of ventricles
What is preload vs afterload
Weight that stretches muscle before it is stimulated to contract
Weight not apparent to muscle in resting state, only encountered when muscle has started to contract
What happens to force (isometric)/shortening(isotonic) as preload and afterload increases
How do you change the steepness of the relationship between shortening and afterload
As preload increases, force increases (until optimum is passed)
As afterload increases, shortening is reduced
Increase preload (longer muscle length) to produce more fore and more shortenings
What are the in Vivo correlates of preload in the heart, what is it dependent on and what measures are there of it
Blood fills heart during diastole, stretching resting ventricular walls, which determines preload on ventricles before ejection
Preload dependent of venous return
Measures include end diastolic volume, end diastolic pressure, right atrial pressure
