cardiac contractility Flashcards
how much greater are the cardiac muscle cell T tubules in diameter in comparison with skeletal muscle cells?
5 times greater (25 times more volume)
what other factor of cardiac muscle cells allow them to accumulate more calcium ions?
the cardiac T tubule mucopolysaccharides
what activates the ryanodine receptors to release calcium ions from the SR in cardiac muscles?
extracellular calcium ions that enter through the voltage gated DHP receptors
how does the sympathetic NS innervate the heart?
innervates the heart muscle and the nodal tissue
what neurotransmitter is released from the sympathetic NS which acts on Beta 1 receptors?
noradrenaline
what does stimulation of the beta 1 receptors result in?
increases cAMP release, enhances Calcium influx into the muscle cell
promotes storage and release of Ca from SR
ULTIMATELY increases force of contraction and speed of relaxation
how is the heart innervated by the parasympathetic NS?
mostly to the SA node
innervates the atria
ULTIMATELY slows the RATE of contraction
can a summation occur in cardiac or skeletal muscle cells?
only in skeletal, not cardiac
what is the absolute refractory period of skeletal muscle cells and cardiac muscle cells?
skeletal muscle cells - 1-2ms
cardiac muscle cells - 245 ms
what is the period of contraction in skeletal muscle cells and cardiac muscle cells?
skeletal muscle cells - 20-100ms
cardiac muscle cells - 250ms
what happens in the relative refractory period?
contraction can occur but the signal has to be stronger to cause an electrical event and the force generated will be smaller
what happens in the period of supernormal excitability?
it takes a smaller signal to cause depolarisation which causes an equal force of contraction
what is diastole?
period of relaxation
what is systole?
period of contraction
what is the percentage of blood filling the ventricles during systole from the atria compared to passively?
80% of ventricular filling is passive
20% is from atrial contraction
what is isovolumnic contraction of the ventricles?
a period of contraction when the AV valve is shut and so is the aortic valve
what is isovolumnic period of relaxation?
when the AV valves are closed but so are the aortic valves but relaxation is still happening without a change in the volume
what is the pulmonary systolic and diastolic pressures?
systolic = 30 mmHg diastolic = 12mmHg
what is End systolic volume (ESV)?
volume in vertical at the end of systole
what is End diastolic volume?
volume in ventricle at the end of diastole
what is stroke volume?
EDV-ESV (quantity of blood expelled per beat in litres)
what is cardiac output?
SV X HR (volume of blood pumped by the heart (L/min)
