Lecture 3 Flashcards
intercalated discs
specialized structures in cardiac muscle cells
intercalated discs contain 2 key types of cell jns
gap junctions = electric coupling
allows functional syncytium = heart contracts as a synchronized unit.
desmosomes = fro strong cell/cell adhesion during contractions,
don’t want cells to rip off from e/o under high force
the big picture of cardiac muscle
pacemaker cells stimulate the contraction. auto rhythmic
heart contracts as a unit, all or none
influx of Ca from extracellular fluid, then triggers Ca release from sacroplasmic reticulum
—- 10-20% of Ca needed to support contraction from ECF = a jumpstart
absolute refractory period.
cannot stimulate a 2nd contractile response, prevents tetanus, relaxation occurs for 250 msec vs 1-2 msec for skeletal. allows it to fn continuously as a pump
relies only on aerobic rep, so coronary circulation is vvvvvv imp.
Contractile cardiac muscle cells
1)depolarization = Na influx through voltage gated channels
positive feedback cycle opens many more Na channels
2)plateau phase
Ca influx, through slow Ca channels
keeps cell depolarized bc few K channels are open
Ca+ in and K+ leaving so almost equal/balanced
3) repolariation
Ca channels inactivate
more K channels open = K efflux
bring voltage of mb back to normal
auto rhythmic vs contractile
contractile = 99% of cells in heart
generate force of contraction
don’t initiate AP, just follow it through
autorhytmic = pacemaker cells
1%
Initiate and regulate heart rhythm
auto rhythmic cells
pacemaker potentials
SA node = rate of pumping
sinus rhythm= det. heart rate
capable of spontaneous depolarization
pacemaker potentials lead to action potentials
AP due to voltage gated Ca channels
auto rhythmic cells steps
1)pacemaker potentials =
slow depolarization is Na channels open and K channels close
mb potential is never a flat line
2)depolarization=
AP begins when pacemaker potential reaches threshold
Ca influx through Ca channels
3)repolarization
Ca channels inactivating
K channels open
K efflux
bring back to (-) voltage.
intrinsic conduction system of heart
AP generated by SA node
passes through AV node
slows down at AV bundle
branches into L/R bundle brancehes
branches further into the purkinje fibres
now called = subendocardial conducting network.
there is a bottleneck from A to V, bc
only 1 pathway
provides time fro A to full V
SA node is te pacemaker bc
the further we get from the node, the slower they spontaneously depolarize
bc it depolaries the fastest + on its own.
on its own, it could be 90x/min, but ParaNS slows down the rate of depolarization
influence of PNS and SNS on cardiac fn
ParaNS = dec depol. rate, slows heart rate
SNS = inc depol. and repol. rate, fastens heart rate
tonic ParaNS output has a dampening effect on heart rate
bradycardia
tachycardia
sinus rhythm
Bradycardia = heart rate slower than usual
tachycardia = heart rate faster than usual
sinus rhythm = normal rhythm of the heart, set by SA node firing.
1 and 2 are variable person to person based on fitness
ECG tracing + events at each step
P-wave = atrial depolarization -NOT CONTRACTING
SA node is firing
QRS complex = ventricular depolarization
atrial depolarization
T wave = ventricular repolarization
abnormal activation of heart
1)ventricular fibrillation =
absolute mess of squiggly and round ups and downs
both V contract at diff times,
absolute mess, can’t just live w it
2) 2nd degree heart block
every 2nd time, the SA node doesn’t get through to AV node, SA is firing but nothing else happens
so P wave, QRS, T wave, P wave ——no activity**, P wave, QRS, T wave, etc,
no activity bc firing doesn’t go through
3)nonfunctional SA node
SA node is damages so AV takes over
no P wave, but everything is slow bc AV spont depolarization is slower than that of SA
at resting, can be lived with, but pacemaker is needed
systole
contraction of heart, pumping out
diastole
relaxation of heart, filling in
cardiac cycle
atrial systole + diastole
+
ventricular systole + diastole
cycle
- ventricular filling. mid to late diastole
Pressure is low, P atria > P vent.
AV valve open
SL valves closed
after vent is 70% full, AV valves begin to close, P wave, and atrial systole.
P atrial inc
final 30% of blood enters w atrial contraction
- ventricular systole = QRS complex and T waves
ventricles contract,
inc P closes AV valves,
is-volumetric contraction = constant volume in a closed system
SL valves open,
ventricular ejection phase - isovolumetric relaxation.
vent. relaxes, early diastole.
P decreases rapidly,
SL valves close to prevent back flow.
chat ai. recap
Atrial Systole (Atrial Contraction)
Atria contract → blood flows into ventricles.
AV valves: Open, Semilunar valves: Closed.
Isovolumetric Contraction (Early Ventricular Systole)
Ventricles contract → pressure rises → AV valves close.
No blood ejected yet.
AV valves: Closed, Semilunar valves: Closed.
Ventricular Ejection (Late Ventricular Systole)
Ventricular pressure exceeds arterial pressure → semilunar valves open.
Blood is ejected into aorta/pulmonary artery.
AV valves: Closed, Semilunar valves: Open.
Isovolumetric Relaxation (Early Diastole)
Ventricles relax → pressure drops → semilunar valves close.
No blood enters ventricles yet.
AV valves: Closed, Semilunar valves: Closed.
Ventricular Filling (Late Diastole)
Ventricular pressure drops below atrial pressure → AV valves open.
Blood flows passively into ventricles.
AV valves: Open, Semilunar valves: Closed.
2 features driving cardiac cycle
blood flow is controlled by P changes
flows from H to low P through any available opening
electrical activity of L/R hearts is almost simultaneous.
heart sounds/
2 distinguishable sounds heard through stethoscope
1st = closure of AV valve, beginging of Vent systole
2nd = closer of SemiLunar valve, end of vent systole
sounds due to vibration of heart/chest bc of valve closer
heart murmurs, due to
vascular insufficiency
leakage of blood back
causes sound where there should be silence
valvular stenoses
valve isn’t opening 100% so there is a narrow opening
high velocity jet of blood through narrow opening
higher pitch of sounds
travels in a swirl instead of a straight line through valve
CO + calc
= cardiac output
volume of blood pumped from each Vent per minute
CO= SV X HR
lets say your heart is beating 75/min = HR
and each contraction/beat is pumping out 70ml/beat = SV
so to find how much blood is pumped from each vent per minute
70 x 75 = 5250 ml/min
SV + calculation
= stroke volume
amount of blood being pumped out w a single contraction
SV= EDV-ESV
EDV = end diastolic volume
ESV = end systolic volume
