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Cardiovascular > Physiology I > Flashcards

Physiology I Flashcards

1
Q

Relative concentrations of Na+, K+, and Ca2+ at resting potential levels (is the concentration of each higher inside or outside the cell?).

A
  • more Na+ outside
  • more Ca2+ outside
  • more K+ inside
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2
Q

What does the Right Coronary Artery supply? What percentage of coronary artery thrombosis occurs here?

A
  • supplies the RV, posterior wall of LV (including the papillary muscle of mitral valve), posterior 1/3 of the IVS, and the SA and AV nodes; 30-40% of thrombosis
  • (thrombosis occurs in LAD > RCA > LCX)
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3
Q

What does the Left Anterior Descending Artery supply? What about the Left Circumflex Artery? What percentage of coronary artery thrombosis occurs in each?

A
  • LAD: supplies the anterior wall of LV, anterior 2/3 of the IVS, apex; 40-50% of thrombosis
  • LCX: supplies the lateral wall of LV; 15-20% of thrombosis
  • (thrombosis occurs in LAD > RCA > LCX)
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4
Q

What path does the conducting system take from start to finish?

A
  • SA node –> internodal pathways –> AV node –> bundle of His –> AV bundle –> bundle branches –> Purkinje fibers
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5
Q

What is the resting potential of a cardiac contractile cell? How does this compare to that of a normal skeletal muscle cell? What is the threshold needed to generate an action potential?

A
  • cardiac cell: -90 mV
  • this is more polarized than skeletal muscle (-85 mV)
  • threshold for action potential = -75 mV
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6
Q

What are the relative (high/low) pressures, resistances, and volumes of arteries, veins, and capillaries?

A
  • arteries: high pressure, low volume (called the stressed volume), low resistance
  • veins: low pressure, high volume (called the unstressed volume), low resistance
  • capillaries: pressure changes from high to low, low volume, high resistance
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7
Q

What are the four determinants of stroke volume?

A
  • preload, afterload, inotropic state, and heart-rate
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8
Q

In an ECG, at which points do the conducting pathway signals occur?

A
  • all of the conducting signals occur in the PR interval
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9
Q

What ECG leads are positive? Which are neutral? Negative?

A
  • positive: I, II, and aVL
  • neutral: aVF
  • negative: III and aVR
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10
Q

How long is the PR interval? The QRS interval? The QT interval?

A
  • PR: 0.2 seconds
  • QRS: 0.12 seconds
  • QT (contains the QRS): 0.4 seconds
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11
Q

What direction does cardiac depolarization occur? What about cardiac repolarization?

A
  • depolarization: endocardium to epicardium

- repolarization: epicardium to endocardium

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12
Q

Why is Troponin-T a better plasma marker of cardiac injury than CK-MB? What is CK-MB used for?

A
  • while both rise rapidly between 4 - 6 hours after injury, troponin-T stays elevated for 7 - 10 days while CK-MB returns to normal after 2 days
  • therefore, CK-MB is a good indicator of a re-infarct occurring within 10 days because troponin levels will already still be high
  • (CK-MB is the gold standard, but troponin can detect an infarct for a longer period of time)
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13
Q

What is cardiac output? What is venous return?

A
  • cardiac output: the rate of blood pumped from either ventricle into the arteries (LV equals RV in the steady state)
  • venous return: the rate of blood returned to either atria via the veins (LA equals RA in the steady state)
  • in the steady state, cardiac output equals venous return
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14
Q

Explain the path of blood flow starting at the left atrium.

A
  • leaves LA through the mitral/bicuspid valve into the LV
  • leaves LV through the aortic valve into the aorta, the systemic arteries, the organs, the systemic veins, and then the vena cava
  • into the RA and then into the RV through the tricuspid valve
  • leaves the RV through the pulmonary valve into the pulmonary arteries, the lungs, and then the pulmonary veins
  • returns to the LA
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15
Q

At rest, what percentage of cardiac output supplies the kidneys, GIT, skeletal muscle, brain, skin, and coronary arteries?

A
  • kidneys: 25%
  • GIT: 25%
  • skeletal muscle: 25%
  • cerebral system (circle of Willis): 15%
  • skin: 5%
  • coronary system: 5%
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16
Q

How can the distribution of cardiac output to certain systems be changed?

A
  • total cardiac output can be increased or decreased (this will increase or decrease the supply to all systems)
  • selective arteriolar resistances can be increased or decreased (this can selectively increase or decrease supply to a certain system and will also result in a decrease or increase of the other systems)
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17
Q

What is the basic structure of an artery? An arteriole? A capillary? A vein?

A
  • artery: very thick-walled, lots of elastic tissue
  • arteriole: extensive smooth muscle
  • capillary: single layer of endothelial cells
  • vein: thin-walled, less elastic tissue
  • (the smooth muscle of arterioles and the venous system is innervated by sympathetic fibers)
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18
Q

Which vessels have the greatest resistance? Which have the greatest capacitance?

A
  • the arterioles have the greatest resistance because of their extensive smooth muscle (this is why the largest drop in pressure occurs between the arteries and the capillaries)
  • the venous system has the greatest capacitance because of the thin walls and less elastic tissue (this means they can hold large amount of blood)
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19
Q

Capillaries have the smallest radius of all the vessels, so blood flowing through here will be the fastest - how, then, can diffusion occur effectively?

A
  • although individual capillaries would technically have rapid blood flow because of their small radius, COLLECTIVELY, capillaries have the largest area (this is called the “t” radius/total radius)
  • thus, once the blood hits the capillary network, it will actually have a SLOWER velocity, thus allowing ample time for diffusion to occur
20
Q

What is the equation for blood velocity? What about flow? Resistance?

A
  • v = Q/A (where Q is flow and A is cross-sectional area)
  • Q = delta P/R (where delta P is change in pressure and R is resistance)
  • therefore, R = delta P/Q
21
Q

What is TPR? How can we calculate it?

A
  • TPR is total peripheral resistance
  • using the equation for resistance, where R = delta P/Q (delta P is change in pressure, Q is flow)
  • TPR = change in pressure between aorta and vena cava / cardiac output
22
Q

How is resistance related to viscosity? To length? To radius? What equation entails this information?

A
  • Poiseuille’s equation: R = (8n*l) / pi r^4
  • n is viscosity, l is length of vessel
  • resistance increases with increasing viscosity and with increasing length
  • resistance decreases immensely with increasing radius
23
Q

What is shear? Where is it most present? Least present?

A
  • shear occurs when adjacent levels of blood within the same vessel travel at different velocities; it occurs because the most resistance to flow is found at the walls of the vessels
  • the most shear occurs at the walls
  • the least shear occurs in the center of vessel (laminar flow)
  • shear breaks up RBC aggregates and decreases blood viscosity
24
Q

What is capacitance? How can we calculate it? As compliance decreases, the pressure for a given volume will do what? What application does this have for the human body?

A
  • capacitance is the volume of blood a vessel can hold at a given pressure; vessels with high capacitance can hold more volume
  • C = V/P (where V is volume and P is pressure)
  • based on this equation: for a given volume, as compliance decreases pressure must INCREASE (this is why arteries have high pressure; this is also why as we age we develop HTN, because as we age arterial compliance continues to decrease - more pressure is needed to hold the same volume as a “young artery”)
25
Q

What are the mean pressures found throughout the systemic circulation? The pulmonary circulation? Explain why the pressure changes as it does.

A
  • systemic: aorta (100 mmHg) –> large arteries (100) –> arterioles (50) –> capillaries (20) –> vena cava (4) –> RA (0-2)
  • pulmonary: pulmonary artery (15) –> capillaries (10) –> pulmonary vein (8) –> LA (2-5)
  • notice the largest pressure drop occurs as we move from the large arteries to the capillaries via the arterioles
  • the pressure decreases throughout these systems because of the consumption of energy in overcoming the frictional resistances of the vessels
26
Q

What are diastolic and systolic pressures? When does each occur? What is pule pressure and what does it reflect? What is mean arterial pressure and how is it calculated?

A
  • diastolic (80 mmHg): the lowest arterial pressure during a cardiac cycle; occurs during ventricular relaxation (when no blood is ejected into the aorta from the LV)
  • systolic (120 mmHg): the highest arterial pressure during a cardiac cycle; occurs during ventricular contraction
  • pulse pressure (40 mmHg): the difference between systolic and diastolic pressures; it reflects the stroke volume
  • MAP (93 mmHg, usually just rounded to 100 mmHg) is the average pressure in a complete cardiac cycle; MAP = 2/3 diastolic + 1/3 systolic (because diastole is longer than systole) OR cardiac output * TPR
27
Q

How does pulse pressure reflect stroke volume?

A
  • (pulse pressure = systolic pressure - diastolic pressure)
  • pulse pressure is the change in arterial pressure when a stroke volume is ejected into the aorta from the LV; therefore larger pulse pressures reflect larger stroke volumes
28
Q

How does arteriosclerosis affect systolic pressure, pulse pressure, and MAP? How about aortic stenosis? Why?

A
  • arteriosclerosis: increases systolic pressure, pulse pressure, and MAP because of decreased arterial compliance (as compliance decreases for a given volume, pressure must increase)
  • aortic stenosis: decreases systolic pressure, pulse pressure, and MAP because of decreased stroke volume
29
Q

Compare the pressure and resistance in the pulmonary and systemic circulations.

A
  • the pulmonary circulation has a much lower pressure than the systemic circulation
  • however, since the cardiac output is the same in both circulations, this means that the resistance of the pulmonary circulation must also be much lower
  • (this is based on the equation Q = delta P/R, where Q is flow or cardiac output, delta P is change in pressure, and R is resistance)
30
Q

What are the two types of cells found in cardiac tissue? Which is more common?

A
  • conducting and contractile cells are present
  • contractile cells make up most of the tissue
  • (conducting cells are in the SA node, atrial internodal tracts, AV node, bundle of His, and Purkinje system)
31
Q

What pathway does electrical conduction take in one cardiac cycle?

A
  • generated at the SA node
  • moves to the RA and LA via the atrial internodal tracts
  • moves to the AV node
  • moves to the bundle of His
  • moves to the Purkinje system and the ventricles
32
Q

What three things must exist for their to be a normal sinus rhythm?

A
  • 1) the action potential must originate in the SA node
  • 2) SA nodal impulses must occur regularly at 60-100 impulses a minute
  • 3) activation of the myocardium must occur in the correct sequence with the correct timing
33
Q

Which ion determines the resting membrane potential of cardiac cells? Which ion’s permeability changes to cause depolarization of the cell?

A
  • K+ determines resting membrane potential

- Na+ permeability increases during conduction to cause depolarization

34
Q

What are the major characteristics of the action potentials of the ventricles, atria, and Purkinje system? What about the SA node?

A
  • ventricles, atria, Purkinje: action potentials are of long duration; contain long refractory periods; contain a plateau phase (a period of sustained depolarization); cycle contains phases 0, 1, 2, 3, and 4
  • SA node: exhibits automaticity; has an unstable resting membrane potential; lacks a plateau phase; cycle contains phases 4, 0, and 3
35
Q

Explain the action potential that occurs in the atria, ventricles, and Purkinje system.

A
  • this occurs in cardiac contractile cells, bundle of His, and Purkinje fibers
  • phase 0 (upstroke): rapid depolarization via Na+ inflow from -85 mV to +20
  • phase 1 (initial repolarization): brief repolarization because Na+ channels close and strong gradient favoring K+ outflow
  • phase 2 (plateau): period of stable depolarization because SLOW L-type Ca2+ channels open (Ca2+ inflow now balances K+ outflow); Ca2+ inflow triggers contraction
  • phase 3 (repolarization): repolarization begins gradually and becomes rapid because the L-type Ca2+ channels close and K+ outflow increases
  • phase 4 (resting): AKA electrical diastole, occurs when the potential is returned to -85 mV
36
Q

Which type of Ca2+ channels do Ca2+ channel blockers block?

A
  • the Ca2+ channel blockers block the SLOW/LONG-LASTING L-type Ca2+ channels used by the atria, ventricles, and Purkinje system
  • they do NOT block the TRANSIENT T-type Ca2+ channels used by the SA node
37
Q

Explain the conduction cycle that occurs in the SA node.

A
  • this occurs in SA and AV nodes (the pacemakers)
  • phase 0 (uptake): depolarization via Ca2+ inflow because of TRANSIENT T-type Ca2+ channels opening (note that this differs from other conduction cycles in that it is Ca2+ instead of Na+ triggering the depolarization, and because the depolarization is less rapid)
  • phase 3 (repolarization): T-type Ca2+ channels inactivate, K+ channels open, resulting in K+ outflow
  • phase 4 (spontaneous depolarization): automaticity; slow depolarization occurs throughout the phase because FUNNY F-type Na+ channels open to cause a slow Na+ inflow (once the threshold potential is reached, T-type Ca2+ channels open and phase 0 begins again)
  • phase 4 is controlled by the autonomic nervous system to set the heart rate
38
Q

What are the latent pacemakers? How is it determined which pacemaker will actually control the heart rate?

A
  • latent pacemakers: AV node, bundle of His, Purkinje system; they all have automaticity but are normally suppressed via overdrive suppression
  • the pacemaker with the fastest rate of phase 4 depolarization controls the heart rate
  • SA (70-80) > AV (40-60) > bundle of His (40) > Purkinje (15-20)
39
Q

What is the conduction velocity in the atria and ventricles? In the AV node? The Purkinje fibers?

A
  • atria and ventricles: 1 m/sec
  • AV node: 0.01-0.05 m/sec (the slowest! this is called slow conduction or AV delay; it gives the ventricles enough time to fill before causing their contraction)
  • Purkinje fibers: 2-4 m/sec (the fastest! this is to make sure the ventricles contract smoothly and quickly once they do fill)
40
Q

What is ARP? ERP? RRP? SNP?

A
  • ARP: absolute refractory period; occurs until the cell repolarizes to about -50mV
  • ERP: effective refractory period; action potential still can’t be generated, but Na+ channels do start to re-open
  • RRP: relative refractory period; a 2nd action potential can be generated, but requires a greater-than-normal stimulus
  • SNP: supranormal period; occurs between -70 and -85mV (resting); action potentials can be generated with a SMALLER stimulus because the Na+ channels have fully recovered and the -70mV is closer to threshold than the resting -85mV
41
Q

What is the difference between an interval and a segment on an ECG?

A
  • intervals include waves, while segments do not

- so the PR interval includes the P wave and PR segment, while the PR segment is simply the PR segment

42
Q

On an ECG, what is happening during the P wave? What does its duration reflect?

A
  • P wave: depolarization of the atria
  • its duration reflects the conduction velocity through the atria (so with decreased velocity, the P wave will be more spread out)
43
Q

On an ECG, what is happening during the PR interval? What does this interval include? What is the normal PR interval?

A
  • PR interval: the time from initial atrial depolarization to initial ventricular depolarization (the conduction delay through the AV node occurs here)
  • contains the P wave (atrial depolarization) and the PR segment (corresponds to AV node conduction time)
  • normal speed: 160 msec
44
Q

On an ECG, what is happening during the QRS complex? What does it’s duration reflect?

A
  • QRS complex (complex of 3 waves): depolarization of the ventricles
  • its duration reflects conduction velocity through the ventricles
  • (note that atrial repolarization occurs during the QRS complex, and is over-shadowed by the ventricular depolarization)
45
Q

On an ECG, what is happening during the T wave?

A
  • T wave: repolarization of the ventricles
46
Q

On an ECG, what is happening during the QT interval? What does this interval include?

A
  • QT interval: the time from initial ventricular depolarization to complete ventricular repolarization (contraction of the ventricles occurs here)
  • contains the QRS complex, T wave, and ST segment
47
Q

On an ECG, how do we measure heart rate? What represents cycle length? How are heart rate and cycle length related?

A
  • heart rate is the number of R waves per unit time
  • cycle length is the interval between two adjacent R waves
  • heart rate = 1 / cycle length

Cardiovascular (11 decks)

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