cardiovascular - lecture 1 Flashcards
what is diastole and systole?
diastole - ventricular relaxation / filling with blood
systole - ventricular contraction / emptying of blood
what are the four valves of the heart?
tricuspid valve (RA -> RV)
mitral valve (LA -> LV)
pulmonary valve (RV -> pulmonary artery)
aortic valve (LV -> aorta)
how do valves operate?
by pressure gradient - close to prevent backflow when pressure would promote it
what are the four heart sounds?
sound 1 - closure of AV valves
sound 2 - closure of pulmonary/aortic valves
sound 3 - early ventricular filling
sound 4 - atrial contraction
what are the layers of the heart wall?
epicardium (external)
myocardium (middle)
endocardium (inner)
what is the epicardium?
thin external layer of heart wall with fat, mesothelial cells, and connective tissue to provide mechanical support (involved with cardiac development and repair)
what is the endocardium?
inner layer with endothelial cells that is the blood-heart barrier
what is the myocardium?
middle layer with cardiac muscle is the bulk of the heart wall, which generates force for pumping and electrical impulses
describe cardiac muscle?
syncytium (multiple nuclei) with branched structures and gap junctions
what is the contraction of cardiac muscle triggered by?
action potentials
how many cells trigger action potentials?
1% are pacemakers, 99% are contractiles
what are the differences between the action potentials of pacemaker cells and contractile myocytes?
pacemakers skip phase 1, are smaller and slower, and having resting potential of -60
contractiles have phases 0-4, are bigger and faster, and have a resting potential of -90
what is the process of action potential forming for slow response (pacemaker) cells?
potential drifts upward to -60, when funny channels open and Na+ influx depolarizes the cell
as it becomes more positive, funny channels close and T-type channels open
at threshold (-40), L-type Ca2+ channels open to cause rapid depolarization
at the peak of AP, Ca2+ channels close and K+ channels open to cause rapid repolarization
what happens in phase 0 for fast response (contractile cells)?
voltage gated Na+ channels open
wave of depolarization moves into cells through gap junction
Na+ enters cells and causes rapid depolarization
what happens in phase 1 for fast response (contractile) cells?
voltage gated Na+ channels close and funny channels open
K+ channels close, very brief depolarization followed by plateau while Ca2+ channels open
what happens in phase 3 for fast response (contractile) cells?
Ca2+ channels close (plateau ends)
slow K+ channels open (causes rapid repolarization)
cell returns to resting membrane potential
what happens in phase 4 for fast response (contractile) cells?
resting potential and ionic concentrations are restored
how does rhythmic excitation move through the heart?
SA node generates AP and it. moves through right atria, left atria and AV node (slows conduction) and prukinje fibres to cause contraction of ventricle myocytes
why does the AV node slow conduction?
to give the blood a chance to pool in the ventricles
how does the AV node slow conduction?
it has less gap junctions
what part of the heart creates impulses?
the SA node is the fastest/best, if it stops working, the AV node will take over, if that stops working, the purkinje fibres will take over
what is an ectopic pacemaker?
a pacemaker not on the sinus node - causes abnormal sequence of contraction
