Flashcards in Physiology I Deck (47):
Relative concentrations of Na+, K+, and Ca2+ at resting potential levels (is the concentration of each higher inside or outside the cell?).
- more Na+ outside
- more Ca2+ outside
- more K+ inside
What does the Right Coronary Artery supply? What percentage of coronary artery thrombosis occurs here?
- 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)
What does the Left Anterior Descending Artery supply? What about the Left Circumflex Artery? What percentage of coronary artery thrombosis occurs in each?
- 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)
What path does the conducting system take from start to finish?
- SA node --> internodal pathways --> AV node --> bundle of His --> AV bundle --> bundle branches --> Purkinje fibers
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?
- cardiac cell: -90 mV
- this is more polarized than skeletal muscle (-85 mV)
- threshold for action potential = -75 mV
What are the relative (high/low) pressures, resistances, and volumes of arteries, veins, and capillaries?
- 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
What are the four determinants of stroke volume?
- preload, afterload, inotropic state, and heart-rate
In an ECG, at which points do the conducting pathway signals occur?
- all of the conducting signals occur in the PR interval
What ECG leads are positive? Which are neutral? Negative?
- positive: I, II, and aVL
- neutral: aVF
- negative: III and aVR
How long is the PR interval? The QRS interval? The QT interval?
- PR: 0.2 seconds
- QRS: 0.12 seconds
- QT (contains the QRS): 0.4 seconds
What direction does cardiac depolarization occur? What about cardiac repolarization?
- depolarization: endocardium to epicardium
- repolarization: epicardium to endocardium
Why is Troponin-T a better plasma marker of cardiac injury than CK-MB? What is CK-MB used for?
- 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)
What is cardiac output? What is venous return?
- 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
Explain the path of blood flow starting at the left atrium.
- 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
At rest, what percentage of cardiac output supplies the kidneys, GIT, skeletal muscle, brain, skin, and coronary arteries?
- kidneys: 25%
- GIT: 25%
- skeletal muscle: 25%
- cerebral system (circle of Willis): 15%
- skin: 5%
- coronary system: 5%
How can the distribution of cardiac output to certain systems be changed?
- 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)
What is the basic structure of an artery? An arteriole? A capillary? A vein?
- 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)
Which vessels have the greatest resistance? Which have the greatest capacitance?
- 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)
Capillaries have the smallest radius of all the vessels, so blood flowing through here will be the fastest - how, then, can diffusion occur effectively?
- 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
What is the equation for blood velocity? What about flow? Resistance?
- 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
What is TPR? How can we calculate it?
- 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
How is resistance related to viscosity? To length? To radius? What equation entails this information?
- 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*
What is shear? Where is it most present? Least present?
- 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
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?
- 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")
What are the mean pressures found throughout the systemic circulation? The pulmonary circulation? Explain why the pressure changes as it does.
- 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
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?
- 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
How does pulse pressure reflect stroke volume?
- (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
How does arteriosclerosis affect systolic pressure, pulse pressure, and MAP? How about aortic stenosis? Why?
- 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
Compare the pressure and resistance in the pulmonary and systemic circulations.
- 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)
What are the two types of cells found in cardiac tissue? Which is more common?
- 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)
What pathway does electrical conduction take in one cardiac cycle?
- 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
What three things must exist for their to be a normal sinus rhythm?
- 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
Which ion determines the resting membrane potential of cardiac cells? Which ion's permeability changes to cause depolarization of the cell?
- K+ determines resting membrane potential
- Na+ permeability increases during conduction to cause depolarization
What are the major characteristics of the action potentials of the ventricles, atria, and Purkinje system? What about the SA node?
- 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
Explain the action potential that occurs in the atria, ventricles, and Purkinje system.
- 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
Which type of Ca2+ channels do Ca2+ channel blockers block?
- 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
Explain the conduction cycle that occurs in the SA node.
- 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*
What are the latent pacemakers? How is it determined which pacemaker will actually control the heart rate?
- 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)
What is the conduction velocity in the atria and ventricles? In the AV node? The Purkinje fibers?
- 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)
What is ARP? ERP? RRP? SNP?
- 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
What is the difference between an interval and a segment on an ECG?
- 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
On an ECG, what is happening during the P wave? What does its duration reflect?
- 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)
On an ECG, what is happening during the PR interval? What does this interval include? What is the normal PR interval?
- 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
On an ECG, what is happening during the QRS complex? What does it's duration reflect?
- 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)
On an ECG, what is happening during the T wave?
- T wave: repolarization of the ventricles
On an ECG, what is happening during the QT interval? What does this interval include?
- 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