Cardio Flashcards
Name the vessel - thick walled, extensive elastic and smooth muscle, under high pressure
Arteries
Name the vessel - site of highest resistance in the cardiovascular system
Arterioles
Name the vessel - largest total cross sectional and surface area
Capillaries
Name the vessel - low pressure, highest proportion of blood in the cardiovascular system
Veins
Express velocity as an equation
V = Q/A
Express blood flow as an equation
Q = delta P/ R OR CO = MAP - RAP / TPR
What drives blood flow?
pressure gradient - flows from high pressure to low pressure
Poiseuille’s Equation
R = 8nl / pie r^4
systemic circulation illustrates what type of resistance?
parallel resistance (1/Rtotal = 1/Ra + 1/Rb + ….. 1/Rn)
Arteries added in parallel causes total resistance to….
decrease
arrangement of blood vessels within an organ illustrates what type of resistance?
series resistance (R total = R artery + R arterioles + R capillaries)
What is the same in each parallel artery?
pressure
Each blood vessel or set of blood vessels in series receives the ________ amount of total blood flow
same
What does Reynold’s number predict?
whether blood flow will be laminar or turbulent
Velocity of blood is ___ at the wall of a vessel and highest at the _____ of the vessel
0; center
Shear is highest at the _____ of the blood vessel
wall
Compliance is inversely related to _____
elastance (higher elastance = lower compliance)
Express compliance as an equation
C = V/P
Compliance is greatest for what type of vessels?
Veins
What happens to pressure as blood flows through the systemic circulation?
pressure decreases progressively b/c of the resistance to blood flow
The largest decrease in pressure occurs across which vessels?
Arterioles (b/c they have the highest resistance; recall Q = delta P / R)
Pulse pressure is defined as
Systolic pressure - diastolic pressure
The most important determinant of pulse pressure is ?
Stroke volume
Define Mean arterial pressure
average arterial pressure with respect to time (MAP = diastolic + 1/3 pulse pressure)
How can left atrial pressure be estimated?
by pulmonary wedge pressure
PR interval
beginning of R wave to beginning of Q wave
What causes variation of the PR interval?
conduction velocity through the AV node
A decreased PR interval (increased conduction velocity through the AV node) can be caused by the stimulation of ?
the sympathetic nervous system
QT interval
beginning of Q wave to end of T wave; entire period of depolarization and repolarization of the ventricles
ST segment
end of S wave to beginning of T wave; period when ventricles are depolarized
T wave represents?
ventricular repolarization
Phase 0, the upstroke of the ventricular AP is caused by?
transient increase in Na+ conductance; INWARD Na+ current depolarizes membrane
Phase 1, the initial repolarization of the ventricular AP is caused by what two factors?
movement of K+ ions OUT of the cell and decrease in Na+ conductance INWARD
Phase 2, the plateau of the ventricular AP is caused by ?
transient increase in Ca2+ conductance – INWARD Ca2+ current and increase in K+ conductance OUT; balanced causing plateau
Phase 3, repolarization of the ventricular AP is caused by?
Ca2+ conductance decreases and K+ conductance predominates - large OUTWARD K+ current
Phase 0, upstroke of SA node AP is caused by?
increase in Ca2+ conductance – INWARD current
Phase 3, repolarization of SA node AP is caused by?
increase in K+ conductance – OUTWARD current
Phase 4, slow depolarization of the SA node AP is caused by?
increase in Na+ conductance – INWARD Na+ current (If)
Phase 4 of the SA node AP accounts for?
pacemaker activity of the SA node
What two phases are not present in the SA node AP?
Phase 1 and 2
Conduction velocity depends on what?
size of the inward current during the upstroke of the AP
Where is conduction velocity the fastest and slowest?
Purkinje system; AV node (to allow ventricals to fill)
What is the absolute refractory period? when does it begin and end?
Begins with upstroke of AP and ends after plateau; time during which no AP can be initiated regardless of inward current supplied
What is the effective refractory period?
a conducted AP cannot be elicited
What is the relative refractory period?
AP can be elicited, but more than the usual inward current is required
Negative chronotropic effect
HR decreases due to decrease rate of phase 4 depolarization; decreased inward Na+ current
Negative dromotropic effect
decreases conduction velocity through the AV node; increases PR interval; decreased inward Ca2+ current and increased outward K+ current
Positive chronotropic effect
HR increases due to increase rate of phase 4 depolarization; increased inward Na+ current
Positive dromotropic effect
increases conduction velocity through the AV node; decreases PR interval; increased inward Ca2+ current
Gap junctions in heart muscle allow it to behave as a ?
electrical syncytium
T/F mitochondria is more numerous in cardiac muscle than in skeletal muscle?
T
During the plateau phase of the AP Ca2+ enters through what type of calcium channels?
L-type calcium channels (dihydropyridine receptors)
Ca2+ that entered through the dihydropyridine receptors in turn activate what channels?
triggers the release of more calcium from the SR through calcium release channels (ryanodine receptors) – Ca2+ induced Ca2+ release
When calcium binds to troponin C what is moved out of the way?
tropomyosin
inotropy refers to …
contractility
How does sympathetic stimulation via B1 receptors increase the force of contraction ?
increases INWARD Ca2+ current during plateau of cardiac AP; also increases activity of Ca2+ pump of the SR
How does digitalis increase force of contaction?
block Na/K ATPase -> intracellular Na+ increases, diminishing Na+ gradient -> Na+/Ca2+ exchange is diminished due to loss of gradient -> increase in intracellular Ca2+
Preload can be defined as ..
end-diastolic volume, which is related to right atrial pressure
Afterload is considered what for the LV and RV?
aortic pressure and pulmonary artery pressure
What determines the maximum tension/force of contraction?
sarcomere length – determines max. number of cross-bridges that can form between actin and myosin
increased contractility leads to what changes as shown on a pressure - volume loop
increased stroke volume which leads to a decrease in end systolic volume
Mean systemic pressure is increased by …
an increase in blood volume or by a decrease in venous compliance (blood is shifted from the veins to the arteries)
Mean systemic pressure is decreased by …
a decrease in blood volume or by an increase in venous compliance (blood is shifted from the arteries to the veins)
The slope of the venous return curve is determined by?
resistance of the arterioles
When TPR is decreased for a given RAP …
there is an increase in venous return (vasodilation of arterioles allows more blood to flow from arteries to veins)
When TPR is increased for a given RAP …
there is a decrease in venous return to the heart (vasoconstriction of the arterioles decreases blood flow from the arteries to the veins and back to the heart)
Affects of positive inotropic agents as seen on a cardiac output curve
produce increased contractility and increased CO; steady state point shifts to a higher CO and a lower RAP (due to more blood being ejected)
Does changes in blood volume or venous compliance change the venous return curve or the cardiac output curve?
venous return curve
Increases in blood volume or decreases in venous compliance leads to?
increase in mean systemic pressure; venous return curve shifts to the right in a parallel fashion; new equilibrium point is reached where both the cardiac output and RAP are increased
Decreases in blood blood volume or increases in venous compliance leads to?
decrease in means systemic pressure; venous return curve shifts to the left in a parallel fashion; new equilibrium point is reached where both cardiac output and RAP are decreased
Changes in TPR alters the cardiac output curve or the venous return curve?
both simultaneously
Increased TPR causes …
a decrease in both cardiac output and venous return; right atrial pressure is unchanged
Decreased TPR causes
an increase in both cardiac output and venous return; right atrial pressure is unchanged
Express stroke volume as an equation
Stroke volume = end diastolic volume - end systolic volume
Express cardiac output as an equation
CO = SV x HR
What is a normal ejection fraction?
55%
What is an ejection fraction?
fraction of end diastolic volume ejected in each stroke volume (ejection fraction = SV / EDV
What is stroke work?
work the heart performs on each beat (stroke work = pressure x volume)
What are the primary energy source for stroke work?
Fatty acids
What is cardiac oxygen consumption directly related to?
amount of tension developed by the ventricles
Cardiac oxygen consumption is increased by what 4 factors?
increased after load, increased size of heart, increased contractility, increased HR
Fick Equation for Cardiac output is
Cardiac ouput = O2 consumption / [O2] pulmonary vein - [02] pulmonary artery
What is the a wave on the venous pulse curve?
the increase in atrial pressure caused by atrial systole
What is the fourth heart sound? is it normally audible?
filling of the ventricle by atrial systole; not audible in normal adults
What corresponds to the first heart sound?
closing of AV valves (ventricular pressure becomes greater than atrial pressure)
Why might the first heart sound be split?
mitral valve closes before the tricuspid valve
What corresponds to the second heart sound?
closure of the aortic and pulmonic valves
What corresponds to the third heart sound? is it normally audible?
rapid flow of blood from the atria into the ventricles causes the third heart sound; normal in children but in adults is associated with disease
What is the longest phase of the cardiac cycle?
reduced ventricular filling
What is responsible for the minute to minute regulation of arterial blood pressure?
baroreceptor reflex
Where are baroreceptors located?
within the walls of the carotid sinus near the bifurcation of the common carotid arteries
A decrease in arterial pressure will lead to what in the carotid sinus?
decrease stretch
A decrease in renal perfusion pressure causes what event to occur?
juxtaglomerular cells of the afferent arteriole to secrete renin
What does renin do?
catalyzes conversion of angiotensinogen to angiotensin I in the plasma
What catalyzes conversion of angiontensin I to angiotensin II in the lungs?
Angiotensin converting enzyme (ACE)
MOA and use of ACE inhibitors? (ex. captopril)
block conversion of angiotensin I to angiotensin II leading to decrease in blood pressure
MOA and use of Angiotensin receptor (AT1) antagonists (ex. Losartan)
block the action of angiotensin II at its receptor and decrease blood pressure
4 effects of angiotensin II
secretion of aldosterone; increases Na+/H+ exchange in the PCT; increases thirst; vasoconstriction of arterioles
Function of aldosterone
increases Na+ reabsorption by the renal distal tubule
chemoreceptors in the carotid and aortic bodies sense?
decreases in PO2
2 effects of vasopressin that tend to increase blood pressure toward normal
potent vasoconstrictor that increases TPR by activating V1 receptors on arterioles; increases water reabsorption by the renal distal tubule and collecting ducts by activating V2 receptors
Where and when is Atrial natriuretic peptide released?
released from the atria in response to an increase in blood volume and atrial pressure
Actions of ANP
relaxation of vascular smooth muscle, dilation of arterioles, decreased TPR, increased excretion of Na+ and water by the kidney, inhibits renin secretion
how do large water-soluble substances cross the capillary wall?
pinocytosis
how do lipid soluble substances like O2 and CO2 cross the capillary wall?
simple diffusion
how do small water soluble substances like water, glucose, and amino acids cross the capillary wall?
water-filled clefts between endothelial cells
Starling equation
Jv = Kf [(Pc - Pi) - (piec - piei)]
nitric oxide is one form of ?
endothelium-derived relaxing factor (EDRF)
What organs exhibit autoregulation?
heart, brain, kidney
What is active hyperemia?
blood flow to an organ is proportional to its metabolic activity
What is reactive hyperemia?
an increase in blood flow to an organ that occurs after a period of occlusion of flow
the most important mechanism of controlling blood flow in the skin
sympathetic control - temperature regulation
effect of histamine on blood flow
arteriolar dilation and venous constriction leads to increased Pc and increased filtration out of capillaries causing edema
effect of bradykinin on blood flow
arteriolar dilation and venous constriction produces increased filtration out of the capillaries causing edema
Is thromboxane A2 a vasodilator or vasoconstrictor?
vasoconstrictor
Coronary circulation is almost entirely controlled by?
local metabolic factors - hypoxia and adenosine
Cerebral circulation is almost entirely controlled by?
local metabolic factors - CO2
What is the primary regulator of blood flow to skeletal muscle at rest?
sympathetic innervation
What type of adrenergic receptors are found on blood vessels of skeletal muscle and what effects to they have?
alpha 1 - vasoconstriction
beta 2 - vasodilation
What is the primary regulator of blood flow to skeletal muscle during exercise?
local metabolic mechanisms - lactate, adenosine, K+
