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118 terms

CR Board Review

The output of the left heart is 100%, what is the output of the right heart?
100%. It is a closed system - the CO of left heart equals the CO of the right heart
Arteries - what do they do?
Deliver oxygenated blood to the tissues.
Arteries - what do they look like?
Thick walled with extensive elastic tissue and smooth muscle
Arteries - What kind of pressure are they under?
Under high pressure (the blood volume contained in the arteries is called the "stressed volume"
Arterioles - what do they do?
Site of highest resistance in the CV system
Arterioles - What do they look like?
Smallest branches of the arteries - have a SM wall
Arterioles - what is their innervation?
SM wall is extensively innervated by autonomic fibers
What regulates arteriolar resistance?
Autonomic NS fibers
What are the two types of ANS receptors found on arterioles and where would they be found?
Alpha-1 Adrenergic receptors are found on the arterioles of the skin, sphanchnic and renal circulations. Beta-2 Adrenergic receptors are found on the arterioles of skeletal muscle
Capillaries - what do they do?
Site of exchange of nutrients, water and gases
Capillaries - how does their structure facilitate their fxn?
Have the largest total cross-sectional surface area. consist of a single layer of endothelial cells surrounded by basal lamina (are thin walled).
What are venules?
Vessels that are formed from merged capillaries
Veins - how are they formed?
Progressively merge to form larger veins. The largest vein (the vena cava) returns blood to the heart
Veins - What do they look like?
Thin walled
Veins - What kind of pressure are they under?
Under low pressure (blood volume contained in the veins is the "unstressed" volume)
Veins - what is special about them?
They contain the highest proportion of blood in the cardiovascular system.
What kind of ANS receptors are found in veins?
alpha-1 adrenergic receptors
What is the "stressed volume" vs the "unstressed volume"?
Stressed volume is found in the arteries, it is under high pressue, unstressed volume is found in the veins, it is under low pressure.
Equation for velocity of blood flow?
V=Q/A (Velocity =blood flow (mL/min)/area (cm3)
What does the equation for blood flow really say?
Velocity is proportional to blood flow and inversely proportional to the cross-sectional area at any level of the CV system.
How do the aorta and capillaries relate in terms of the equation for velocity?
Blood velocity is higher in the aorta (smaller cross sectional area) then in the sum of all the capillaries (large cross sectional area). The lower velocity of blood in the capillaries optimizes conditions for exchange of substances across the capillary wall.
Equation for blood flow?
Q=change in P/R or cardiac output= mean arterial pressure-right arterial pressure/TPR
Ohm's Law
I=V/R (same as equation for blood flow where flow is current and pressure is voltage)
What drives the blood through the body?
Pressure gradient (change in P) the blood flows from high pressure to low pressure.
What is blood flow inversely proportional to?
Resistance of the blood vessels.
What equation is used to calculate resistance?
Poiseuille's equation
What is resistance directly proportional to?
Viscosity of blood (increasing viscosity by increasing hematocrit will increase resistance and decrease blood flow. It is also proportional to length of vessel.
What is resistance inversely proportional to?
The 4th power of the vessel radius. Powerful relationship! If the blood vessel radius decreases by a factor of 2, then resistance increases by a factor of 16!
What does it mean that the organs run in parallel in terms of resistance?
Each organ is supplied by an artery that branches off the aorta. Each artery in parallel receives a fraction of the total blood flow. When an artery is added in parallel, the total resistance decreases. In each parallel artery, the pressure is the same.
What equation illustrates resistance in parallel?
1/Rtotal = 1/Ra + 1/Rb.... so the total resistance is less than the resistance of any of the individual arteries.
What does it mean for the blood vessels within an organ to run in series in terms of resistance?
Each organ is supplied by a large artery, smaller arteries, arterioles, capillaries, and veins arranged in series. The total resistance is the sum of the individual resistance Rtotal = R1+R2...
What ios the largest proportion of resistance in the blood vessel series?
How much bloos flow does each vessel in series get?
Each blood vessel (largest artery) or set of blood vessels (all the capillaries) in series receive the same total blood flow. Thus, blood flow through the largest artery is the same as the total blood flow through all the capillaries.
What happens to pressure as blood flows through a series of blood vessels?
The pressure decreases
What is the difference b/w laminar flow and turbulent flow?
Laminar flow is streamlined (in a straight line) turbulent flow is not
What is Reynolds number and how is it used?
Predicts whether blood flow will be laminar or turbulant. Increased Reynold's number = greater tendency for turbulence
What are bruits?
Audible vibrations caused by turbulent blood flow
What factors increase reynold's number/turbulence?
Decreased blood viscosity (low hematocrit/anemia). Increased blood velocity (narrowing of a vessel)
What is capitance? How is it related to elastance?
Compliance, describes the dispensability of blood vessels. The opposite of elastance (stiffness). The greater the amount of elastic tissue there is in a blood vessel, the higher the elastance is, and the lower the compliance is.
What equation describes capacitance?
C=V/P (capitance = volume/pressure)
What does the equation for capacitance really say?
Capacitance is directly proportional to volume and inversely proportional to pressure. (Describes how volume changes in response to a change in pressure)
Where is capacitance higher and lower? How does this effect where most of the blood is found in the body?
Capitance is much greater for veins than for arteries. As a result, more blood volume is contained in the veins (unstresssed volume) then in the arteries (stressed volume)
What happens if there is a change in the capacitance of the veins?
Changes in capacitance of veins produces changes in unstressed volume. (A decrease in venous capitance decreases the unstressed volume and increases the stressed volume by shifting blood from the arteries to the veins)
How does age affect the capacitance of arteries?
Capacitance of the arteries decreases with age. As a person ages, the arteries become stiffer and less distensible.
Why does pressure decrease as the blood flows through systemic circulation?
Pressure decreases progressively b/c of the resistance to blood flow.
Where is pressure highest? Lowest?
Highest in the aorta/large arteries and lowest in the vena cavae.
Where does the largest drop in pressure occur and why?
Across the arterioles b/c they are the site of highest resistance.
What are the mean pressures in the systemic circulation for:
1. Aorta
2. Arterioles
3. Capillaries
4. Vena Cava
1. 100 mm Hg
2. 50 mm Hg
3. 20 mmHg
4. 4 mmHg
What are two characteristics of arterial pressure?
1. It is pulsatile
2. it is not constant during the cardiac cycle (there is a diastole/systole)
What is systolic pressure and when is it measured?
The highest arterial pressure during a cardiac cycle. Measured after the heart contracts (systole) and blood is ejected into the arterial system
What is diastolic pressure and when is it measured?
The lowest arterial pressure during a cardiac cycle. Meaured when the heart is relaxed (diastole) and blood is returning to the heart via the veins.
What is the pulse pressure?
Difference b/w systolic and diastolic pressures
What is the most important determinant of pulse pressure?
Stroke volume. As blood is ejected from the left ventricle into the arterial system, arterial pressure increases b/c of the relatively low capitance of the arteries. B/c diastolic pressure remains unchanged during ventricular systole, the pulse pressure increases to the same extent as the systolic pressure.
What is an example of what could cause increases in pulse pressure?>
Decreases in capacitance, such as those that occur with the aging process can increase pulse pressure.
What is mean arterial pressure?
The average arterial pressure with respect to time.
How do you estimate MAP?
Diastolic pressure plus 1/2 of pulse pressure.
What are two characteristics of venous pressure?
1. It is very low
2. The veins have high capacitance and therefore can hold large volumes of blood at low pressure.
What is the pressure like in the atria?
Slightly lower than venous pressure
How do you estimate left atrial pressure?
Pulmonary wedge pressure. A catheter, inserted into the smallest branches of the pulmonary artery makes almost direct contact with the pulmonary capillaries. The measured pulmonary capillary pressure is approximately equal to the left arterial pressure.
ECG: What does the P wave represent?
Atrial depolarization (does not include atrial repolarization - which is buried in the QRS complex)
What is the PR interval? What does it represent?
Interval from the beginning of the P wave to the beginning of the Q wave. - inital depolarization of the ventricle.
what changes the PR interval?
Varies with conduction velocity through the AV node. (If AV nodal conduction decreases (as in heart block) the PR interval increases.
How does the ANS influence the PR interval?
Decreased (increased conduction velocity through AV node) by stimulation of the sympathetic NS. Increasesd (decreased conduction velocity through AV node) by stimulatiion of the parasympathetic NS
What does the QRS complex represent?
Depolarization of the ventricles
What is the QT interval and what does it represent?
Interval from beginning of the Q wave to the end of the T wave . Represents the entire period of depolarization and repolarization of the ventricles
What is the ST segment? What does it represent?
Segment from the end of the S wave to the beginning of the T wave. Is isoelectric. Represents the period when the ventricles are depolarized.
What does the T wave represent?
Ventricular repolarization
What determines the RMP of cardiac cells?
The conductancce of potassium. Approaches the potassium equilibrium potential.
What does inward vs. outward current do to the RMP?
Inward current brings positive charge into the cell and depolarizes the membrane potential. outward current takes positive charge out of the cell and hyperpolarizes the membrane potential.
What is the role of sodium, potassium ATPase?
Maintains ionic gradients across cell membranes
Descrive the RMP and APs of the ventricles, atria, and purkinje system.
Have stable RMP of about -90mV (approaches the potassium equilibrium potential) APs are of long duration, esp in purkinje fibers where they last 300 msec
What are the phases of APs in ventricles, atria and purkinje system?
Phase 0 (upstroke)
Phase 1 (initial repolarization)
Phase 2 (Plateau)
Phase 3 (Repolarization)
Phase 4 (RMP)
Describe phase O in ventricles, atria and purkinje system
The upstroke of the AP, caused by transient increase in sodium conductance. This increase results in an inward sodium current that depolarizes the membrane. At the peak of the AP, the membrane potential approaches the sodium equilibrium potential
Describe phase 1 in ventricles, atria and purkinje fibers
Brief period of initial repolarization. Initital repolarization is caused by an outward current, in part b/c of movement of potassium ions (favored by both chemical and electrical gradients) out of the cell and in part b/c of a decrease of sodiumn conductance.
Describe phase 2 in ventricles, atria and purkinje fibers
Plateau of AP. Caused by transient increase in calcium conductance, which results in inward calcium current, and by an increase in potassium conductance. During phase 2, outward and inward currents are approx equal so the membrane potential is stable at the plateau level.
Describe phase 3 in ventricles, atria and purkinje fibers
repolarizatio. Calcium conductance decreases, potassium conductance increases and therefore predominates. The high potassium conductance results in a large outward potassium current, which hyperpolarizes the membrane back toward potassium equillibrium potential
Describe phase 4 in ventricles, atria and purkinje system.
Is the RMP, is a period during which inward and outward currents of potassium are equal and the membrane potential approaches the potassium equillibrium potential.
Describe the resting potential of the SA node?
It is normally the pacemaker of the heart, it has an unstable resting potential. Exhibits phase 4 depolarization or automaticity
What are the latent pacemakers of the heart?
The AV node and the His-purkinje system. May exhibit automaticity and override the SA node if it is suppressed
Where is the intrinsic rate of phase 4 depolarization the fastest? The slowest?
Fastest at SA, then AV, then His-Purkinje system
Describe phase 0 in the SA node
Upstroke of the AP, caused by increase in CALCIUM conductance. This increase causes an inward calcium current that drives the membrane potential toward the calcium equilibrium potential. (This is different than the V/A/P where it is inward SODIUM current)
Describe phase 3 in the SA node
Repolarization, is caused by an increase in potassium conductance. Increase results in outward potassium current that causes repolarization of the membrane potenital.
Describe phase 4 in the SA node
Slow depolarization. Accounts for the pacemaker activity of the SA node (automaticity). Caused by an increase in sodium conductance, which results in an inward sodium current called "funny current = If) If is turned on by repolarization of the membrane potential during the preceding AP
What creates the upstroke of the AP in the AV node?
Inward calcium current (as in the SA node)
What is conduction velocity and what does it depend on?
Reflects the time required for excitation to spread throughout cardiac tissue. Depends on the size of inward current during the upstroke of the AP. The larger the inward current, the higher the conduction velocity.
Where is the conduction velocity fastest? Slowest? Why?
Fastest in the purkinje system. SLowest in the AV node (seen as the PR interval on the ECG), allowing time for ventricular filling before ventricular contraction (if conduction velocity through the AV node is increased, ventricular filling may be compromised).
What is excitiability"? What causes it? Is it always the same?
The abilility of cardiac cells to initiate APs in response to inward, depolarizing current. Reflects the recovery of channels that carry the inward currents for the upstroke of teh AP. Changes in the course of the AP (refractory periods)
What are refractory periods and what are the three types?
Changes in excitability of cardiac cells over the course of the AP
1. Absolute refractory period (ARP)
2. Effective refractory period (ERP)
3. Relative refractory period (RRP)
What is the absolute refractory period?
Begins with the upstroke of the AP and ends after the plateau. Reflects the time during which no AP can be initiated, regardless of how much inward current is supplied.
What is the effective refractory period?
Slightly longer than the ARP. The period during wich a conducted AP cannot be elicited.
What is the relative refractory period?
The period immediately after the ARP when repolarization is almost complete. The period during which an AP can be elicited, but more than teh usual inward current is required.
What are chronotropic effects?
Produce changes in heart rate (negative decreases heart rate by decreasing the firing rate of the SA node/ positive increases heart rate by increasing the firing rate of the SA node)
What are dromotropic effects?
Produces changes in conduction velocity, primarily the AV node. (negative decrease conduction velocity through AV node, slowing conduction of AP from atria to the ventricles and increasing the PR interval/positive will do the opposite)
What parts of the heart have parasympathetic vagal innervation? What parts do not?
SA node, atria, and AV nodes have it, ventricles do not
What is the NT and receptor for the parasympathetic vagal innervation of the heart?
Acetylcholine (ACh), acts at muscarinic receptors
What are the parasympathetic effects on heart rate and conduction velocity?
Negative chronotropic effect (decreased HR) negative dromotropic effect (decreases conduction velocity through the AV node - increases the PR interval)
How does the parasympathetic system create a negative chronotropic effect on the heart?>
Decreases HR by decreasing the rate of phase 4 depolarization. Fewer APs occur per unit time b/c the threshold potential is reached more slowly and, therefore, less frequently. The mechanism is decreased funny current, the inward sodium current that is responsible for phase 4 depolarization in the SA node.
How does the parasympathetic system create a negative dromotropic effect on the heart?
Decreases conduction velocity through the AV node, APs are conducted more slowly from atria to ventricles. Increases the PR interval. The mechanism of the negative dromotropic effect is decreased inward calcium current and increased outward potassium current.
What are the sympathetic effects on heart reate and conduction velocity?
Positive chronotropic effect (increased HR), positive dromotropic effect (increased conduction velocity through AV node - decreases PR interval)
How does the sympathetic system create a positive chronotropic effect on the heart?
Increases HR by increasing the rate of phase 4 depolarization. More APs occur per unit time b/c the thershold potential is reached more quickly, and therefore more frequently. Mechanism is increased funny current, the inward sodium current responsible for phase 4 depolarization
How does the sympathetic NS create a postive dromotropic effect on the heart?
Increases conduction velocity though the AV node. APs are conducted more rapidly from the atria to the ventricles, and ventricular filling may be compromised. Decreases PR interval. The mechanism of the positive dromotropic effect is increased inward calcium current.
What is the sarcomere?
Contractile unit of the myocardial cell. Similar to the contractile unit in skeletal muscle in that it runs from Z line to Z line and contains thick and thin filaments
How does contraction occur in the sarcomere?
Just like it does in skeletal muscle, shortening occurs according to the sliding filament model (thin filaments slide along adjacent thick filaments by forming and breaking cross bridges b/w actin and myosin)
What are intercalacted discs?
Occur at the ends of cells, maintain cell to cell cohesion. Contain gap junctions
What accounts for the bx of the heart as an electrical syncytium?
Gap junctions. Present at the intercalacted discs. Are low-resistance paths b/w cells that allows for rapid electrical spread of APs
Compare cardiac and skeletal muscle in terms of mitochondria
More numerous in cardiac muscle than in skeletal muscle
What are t-tubules, where are they and what do they do?
Continuous with the cell membrane, invaginate the cells at the Z lines and carry APs into the cell interior. Are well developed in the ventricles but poorly developed in the atria. From dyads with the sarcoplasmic reticulum.
What is a dyad?
connection b/w t-tuble and SR
What is the sarcoplasmic reticulum and what does it do?
Small diatmeter tubules in close proximity to the contractile elements. Are the site of storage and release of calcium for excitation contraction coupling
What are the 7 steps in excitation/contraction coupling?
1. AP spreads from cell membrane into the t-tubules 2. At plateau of AP, Ca conductance is increased and Ca enters the cell from the ECF 3. Entry of Ca triggers release of more Ca from the SR (Ca induced Ca release). 4 Intracellular Ca increases 5. Ca binds to troponin C, tropomyosin moves out of the way, removing inhibition of actin/myosin binding. 6 Actin and myosin bind, the thick and thin filaments slide past eachotehr and the myocardial cell contracts. The magnitude of tension that develops in proportional to the intercellular Ca. 7. relaxation occurs when Ca is re-accumulated by the SR by an active Ca ATPase pump
What determines how much Ca is released by the SR and what effect doe the amount released cause?
The amount of Ca released from the SR depends on the amount of Ca previously stored and on the size of the inward Ca current during the plateau of the AP. The magnitude of tension that develops is proportional tyo the intercellular Ca
What is contractility? Another name for it? What is it related to?
The intrinsic ability of cardiac muscle to develop force at a given muscle length. Aka inotropism. Related to the intercellular Ca concentration
How can contractility be estimated?
By the ejection fraction (stroke volume/end-diastolic volume)
What is a normal ejection fraction?
.55 (55%)
What are positive vs negative inotropic agents?
positve produce an increase in contracility while negative produces a decrease
What are three factors that increase contractility (positive ionotropism)
1. Increased HR
2. Sympathetic stimulation (catecholamines) via beta 1 receptors
3. Cardiac glycosides (digitalis)
How does an increasesd HR increase contractility?
When more APs occur per unit time, more Ca enters the myocardial cells during AP plateus, more Ca is released fro SR and greater tension is produced during contraction
How does sym