The Heart Flashcards
what is the heart?
pumps blood around the body to supply the tissues
pumps blood to the lungs so that it can be oxygenated
How does the heart do this?
it is a muscular pump
cardiac muscle is made up of 2 interdepend interconnecting network of mm fibres called a syncytium
each syncytium contracts as a unit. When one muscle fibres is stimulated the whole syncytium contracts, e.g atrial syncytium
the syncitia are electrically stimulated from each other to prevent simultaneous contraction. e.g atrium can contract without the ventricles
What is cardiac muscle?
muscle fibres are short in length branched connected by intercalated discs which anchor muscle fibres together gap junctions allow AP to pass between fibres Anti and myosin Autorhythmic fibres self excitability cardiac cells depolarise rhythmically heart beats continually
What is the function of cardiac muscle?
pacemaker
conduction system
What are contractile fibres?
different AP in order to allow for a coordinated pump action
resting membrane potential of -90mV
AP in adjacent fibre passes via gap junction and opens the sodium channel
rapid inflow of sodium flow into the muscle cell
causes rapid depolarisation of fibre
Action Potential
lasts 0.25 seconds longer in cardiac than skeletal due to the transport of ions inside the cell
this results in a plateau:
Na is being pumped out of the cell
Na slowly enters the cell balancing the loss of Na
balancing the membrane potential at 0mv
K remains in the cell
depolarisation cannot occur
Repolarisation
only occurs when calcium channels close and calcium stops coming into the cell resulting in K channels opening so K can leave the cell resting membrane potential is restored cell can start repolarising
refractory period
depolarisation can’t occur agin until venous return is back in the heart
lasts longer than the contraction
fibres are in relaxation before next contraction can occur
allows pumping action of cardiac mm
SA node disease
can stop acting as a pacemaker
AV node can take over at 40-60bpm
both suppressed ventricles will beat at 20-30bpm
insufficient blood to brain-pacemaker
Atrial fibrillation
no coordinated contraction of atria so don’t get P wave
on drugs to prevent clots
Ventricular tachycardia
ventricles don’t have time to fill before each beat
equivalent of cardiac arrest
heart beats too quickly
no cardiac output
Ventricular fibrillations
most common cause of cardiac arrest
ventricular myocites are quivering so aren’t producing a pumping action or cardiac output
need a defibulator
Co-ordination of contraction
AP needs to be coordinated for heart to act as an effective pump
chambers of the heart need to contract in sequence: atria needs to contract to fill ventricles and ventricles need to contract once full
SA node is a pacemaker of the heart
specialised muscle cells in the SA node depolarise auto rhythmically 100APs per minute
slowed to around 75 by vagus nerve- slows down SA depolarisation
Conduction of SA node potential
when SA node depolarises the atria contract
atria are insulated from ventricles so ventricles don’t contract
AP passes along the internodal pathways and gets to the atria ventricular bundle
From AV bundle to the bundle of his
AV node delays impulse which allows atrial contraction to fill ventricles before they contract
impulse goes down bundle of his, into L and R bundle branches and out into purkinje fibres where speed of contraction is 6 x faster through the ventricular muscles
all the muscle contracts from the apex to the aortic pulmonary valves
