Nordgren Cardiac Physiology Flashcards
What is Starling’s Law of the Heart?
If cardiac filling increases during diastole, the volume ejected during systole also increases.
–the heart pumps what it recieves
State the equation for resistance with respect to length (L), viscosity (n), and radius (r).
R = 8Ln/ (pi)r^4
Stroke Volume = ?
EDV (end diastolic volume) - ESV (end systolic volume)
Cardiac output = ?
SV x HR
5 requirement for effective heart operation?
- contractions of cardiac myocytes must be synchronized and occur at regular intervals (not arrhythmic)
- The valves must open fully (not stenotic)
- Valves must not leak (not insufficient or regurgitant)
- Contraction must be forceful (not failing)
- Ventricles must fill adequately during diastole
Total blood volume in an average adult?
5 L ~ 8% total body weight
Flow (Q) = ?
change in pressure / resistance
What ion is responsible for rapid depolarization of myocardial contractile cells?
Na+
What ion is responsible for rapid depolarization of myocardial pacemaker cells?
Ca2+
What are the 5 phases of contractile cells?
4 -- resting potential (~ -90 mV) 0 -- depolarization (influx of Na+) 1 -- peak 2 -- plateau (slow influx of Ca2+) 3 -- rapid repolarization (K+ outflow) 4 -- resting again (K+ inward rectifier channels open)
What are the 3 phases of pacemaker cells?
4 – funny current channels open (more Na+ in than K+ out, net depolarization but gradual), transient Ca2+ channels open (influx) **pacemaker potential
0 – long lasting Ca2+ channels open at threshhold of -30 mV –> depolarization
3 – K+ channels open –> repolarization
4 – funny current channels open again
What is the pacemaker node and where is it?
SA node in right atrium
Where is Bachman’s Bundle?
left atrium
Where does the action potential go immediately after the AV node?
Bundle of His
What structure allows passage of AP from cell to cell?
gap junctions
Gap junctions and what other structure form intercalated discs?
desmosomes
Anchoring sites for actin, connect to closest sarcomere:
Fascia Adherens
join cells together by binding intermediate filaments:
Macula Adherens
protein that forms gap junctions:
connexin
Why does AP slow through AV node?
fewer gap junctions than SA node and atrial myocardium
tissue with fastest conductance?
Bundle of His and Purkinje fibers– 4 m/sec
nerve and NT in control of cardiac parasympathetic response:
vagus
Acetylcholine
**increase permeability of resting membrane to K+
**decrease diastolic funny current through HCN channels
NT involved in cardiac sympathetic response:
norepinephrine
**increases diastolic funny current through HCN channels
**shortens time to depolarization
Ca2+ enters myocyte via ________ channel.
L-type
Ca2+ released from SR via _________ channels.
ryanodine receptor channels (RyR)
Ca2+ ions bind to ______________ to initiate contraction.
Troponin
Ca2+ exchange with Na+ via the ____________.
NCX antiporter
passive/resting tension placed on cardiac muscle cells before contraction (a function of volume and pressure at the end of diastole):
Preload
the active tension placed on cardiac muscle cells during contraction (a function of the resistance the left ventricle must overcome to circulate blood):
Afterload
The total ventricular wall tension (T) depends on both intraventricular pressure (P) and the internal ventricular radius (r)— T = P x r
…this is known as:
The law of Laplace
Positive chronotropic effect:
NE increases rate of spontaneous depolarization of membrane–shortens time to depolarization
increases HR
Isometric contraction:
Activation of muscle whose ends are held rigidly
can develop tension
cannot shorten
Isotonic contraction:
activation of unrestrained muscle causes it to shorten without force development because it has nothing to develop force against
Inotrope:
influences the amount of tension a muscle can develop and the amount of shortening a muscle can achieve
ie: NE has a positive inotropic effect–increses afterloaded shortening, increases isometric tension
Positive dromotropic effect:
an increase in the rate of action potential conduction
particularly evident in the AV node
