Circulation, Cardiac Muscle, Rhythmical Excitation, Cardiac Cycle

Systemic Circulation makes up -% of where blood is, with -% in the -

84, 64, veins

Velocity of blood flow formula is what?

V=F/A, velocity is equal to blood volume divided by CSA

Which section of circulation has the largest CSA? why?

Capillaries, for gas/nutrient exchange

Are veins or arteries more distensible?

Veins are 8x as distensable

Where in circulation is pressure high?

Where is it low?

Where does it have to fluctuate up and down from zero?

High: LV, aorta, arteries, arterioles

Low: capillaries all the way to LV

Fluctuates from 0: at the ventricles specifically (contracted vs relaxed)

What is cardiac output, how is it calculated, and what is average?

CO is amount of blood pumped into the aorta each minute, CO=HR*SV=MAP/TPR, average is 4-6 L/min

Describe Ohm’s Law!

Flow=change in pressure/resistance

What are the two ways blood can flow?

Laminar (parabolic) and turbulent (all directions)

In poiseuille’s law, what is the biggest factor influence blood flow?

Radius (^4)

What is systemic vascular resistance?

• Another name?

The total resistance to blood flow systemically, 2/3 due to arterioles

• Total peripheral resistance (TPR)

What is the name for the ability of organs to maintain relatively constant blood flow despite arterial BP changes?

Autoregulation

List the path of conduction system in the heart

SA→AV→Bundle of His→Bundle Branches→Purkinje fibers

What are the three layers of the heart?

Endocardium, Myocardium, Epicardium

What are the two types of myocardial cells?

Conducting and contracting cells

Cardiac muscle is -, has - - with - -, and displays the characteristic of two -

Striated, intercalated discs with gap junctions, ‘syncytia’

AP for cardiac muscle cells start at -, use - and - for depolarization, and have a - (-/- balance) before repolarization

-90, Na+ and Ca2+, plateau (Ca2+/K+)

Why is there a long refractory period/long AP?

Prevents tetanus

Describe excitation-contraction coupling

T tubules bring extracellular Ca2+ in, SR releases its own Ca2+ which binds to troponin. This moves tropomyosin, exposing actin to myosin heads for sarcomere to shorten (muscle contracts)

Strength of cardiac muscle contraction depends on availability of what?

Local extracellular Ca2+

Describe AP of pacemaker cells!

RMP closer to threshold due to funny current (-60), Ca2+ channels open at threshold, K+ open to repolarize

Why does the AV node delay signal for ~0.16 seconds?

Allows time for ventricular filling

Bundle branches conduct - for - - -, SA -, AV -

Rapidly for synchronous ventricular contraction, Moderate, Slowly

What is the discharge rate of SA (pacemaker), AV, Purkinje?

60-100, 40-60, 15-40

What are ectopic pacemakers and why are they problematic?

Group of overly excitable cells outside the SA node that drastically alter contraction rhythm of heart

How does parasympathetic system alter heart function?

Ach released from vagal nerves causes increased leakage of K+. This slows sinus node rate and transmission to the ventricles

How about sympathetic?

NE: Increases sinus node discharge, speed of conduction, level of excitability, force of contraction

What are the approximate mL for EDV, ESV, SV!

EDV: 100-120 (liquid in LV after relaxed)

ESV: 40-50 (liquid in LV after contraction)

SV: 70 (liquid ejected from LV)

How is stroke volume calculated?

SV= EDV-ESV

Describe the EKG phases!

P wave: atrial depolarization

PR segment: av node delay

QRS complex: ventricular depolarization

T wave: ventricular repolarization

L vs R ventricular pressures… go!

L: 80 mmHg

R: 8 mmHg

What is ejection fraction? How is it calculated?

Amt of blood pumped out of LV compared to what was in it before

EF=(SV/EDV)*100%

What is a typical EF value? how about subvalues (2)?

50-70, 41-49 is mildly reduced, below 40 is reduced (no PA)

What is typical duration of systole/diastole? How does it change with PA?

systole 40%, diastole 60%; systole increases relatively with PA

AV valves prevent backflow from - into -, SL valves from - into -

Ventricles into atria, aorta/pulmonary arteries into ventricles

Lub (S1) and Dub (S2) are what?

Lub is AV closure, Dub is SL closure

LV volume pressure diagram.. explain!

Filling: increasing volume, no change in pressure

Isovolumetric contraction: no change in volume, increased pressure

Ejection: decreased volume, increasing pressure

Isovolumetric relaxation: no change in volume, decreased pressure

What are preload and afterload?

Preload: volume returning to heart from circulation

Afterload: resistance LV must overcome to circulate

Describe the Frank Starling Mechanism?

More heart stretch from filling creates stronger contraction

What is mean arterial pressure?

• How is it calculated?

Average BP in one cardiac cycle (average is 70-110 mmHg)

• MAP = (SBP+ (2*DBP)) / 3 = CO*TPR

What do these things do to HR?

• K+, Ca2+, Temps

K+: decreased

Ca2+: increased

High temp: increased

Low temp: decreased