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199 Cards in this Set

  • Front
  • Back
What is the relationship between the cardiac outputs of the left and right sides of the heart?
They are equal
Which sides of the heart are responsible for which circulations?
Left heart: systemic circulation
Right heart: pulmonary circulation
What is the course of blood flow?
Left atrium
Left ventricle (mitral valve)
Aorta (aortic valve)
Systemic arteries and tissues
Systemic veins
Vena cava
Right atrium
Right ventricle (tricuspid valve)
Pulmonary artery (pulmonic valve)
Lungs
Pulmonary vein
What is the function of the arteries?
Deliver oxygenated blood to the tissues under high pressure
What types of walls do arteries have?
Thick walls, with extensive elastic tissue and smooth muscle
What is the "stressed volume?"
The volume of blood contained in the arteries
What are the smallest branches of the arteries?
Arterioles
What is the site of highest resistance in the cardiovascular system?
Arterioles
Describe the important features of the arteriolar walls
Smooth muscle is extensively innervated by the ANS
What types of adrenergic receptors are found in the arterioles?
alpha 1: skin, splanchnic, and renal arterioles
beta 2: skeletal muscle arterioles
What part of the cardiovascular system has the largest total cross-sectional and surface area?
Capillaries
What are some important features of capillary walls?
Single layer of endothelial cells
Thin walls
Site of exchange for nutrients, water, and gases
What are venules?
Formed from merged capillaries
What part of the cardiovascular system contains the highest amount of blood?
Veins
What are some important features of veins?
Progressively merge to form larger veins, the largest of which is the vena cava
Low pressure
Thin-walled
What is the "unstressed volume?"
The volume of blood contained in the veins
Formula for the velocity of blood flow
V = Q/A
Q = blood flow
A = cross-sectional area
Velocity is directly proportional to blood flow and inversely proportional to the cross-sectional area
Where in the cardiovascular system is blood velocity the highest?
The aorta, because the cross-sectional area is the smallest
What is the driving force for blood flow?
A pressure gradient. Blood flows from high to low pressure
How does blood flow relate to the resistance of blood vessels?
Blood flow is inversely proportional to resistance
Are most organ resistances in series or in parallel?
In parallel (except for the kidneys)
Where in the body do we find resistances in series?
Blood vessels within a given organ (that is supplied by one artery)
What is the difference between laminar and turbulent flow?
Laminar flow moves in straight lines or lamina, and turbulent flow does not
What are bruits?
Audible vibrations in the blood vessels due to turbulent flow
How does blood velocity affect Reynold's number?
Increased velocity (from narrowing of a vessel) increases Reynold's number
Which has greater capacitance, veins or arteries?
Veins, so more blood volume is contained in the veins
What happens if there is a decrease in venous capacitance?
This decreases unstressed volume, so blood is shifted from the veins to the arteries
What happens to the capacitance of arteries with age?
Decreases (they become stiffer, more elastic)
Where in the cardiovascular system is pressure the highest? The lowest?
Highest in the aorta and large arteries
Lowest in the venae cavae
What is the mean pressure of the aorta?
100 mmHg
What is the mean pressure of the arterioles?
50 mmHg
What is the mean pressure of the capillaries?
20 mmHg
What is the mean pressure of the vena cava?
4 mmHg
What happens to arterial pressure over the course of a cardiac cycle?
It fluctuates and is not constant; it is pulsatile
What is systolic pressure?
Measured after heart contraction (systole) and blood is ejected into the arterial system
This is the highest arterial pressure in the cardiac cycle
What is diastolic pressure?
Measured when the heart is relaxed (diastole) and blood is returning to the heart via the veins
This is the lowest arterial pressure in the cardiac cycle
What is the pulse pressure?
The difference between the systolic and diastolic pressures
What is the most important determinant of pulse pressure?
Stroke volume
As blood is ejected from the left ventricle, arterial pressure increases because the arteries have relatively low capacitance (ie systolic pressure increases)
Diastolic pressure stays the same
What happens to pulse pressure as we age?
It increases because the capacitance of the arteries decreases
What is the mean arterial pressure?
The average arterial pressure over time
Why is venous pressure so low?
The veins have high capacitance
What is pulmonary wedge pressure?
A way of estimating left atrial pressure (should be slightly lower than venous pressure). A catheter is inserted into the smallest branches of the pulmonary artery, and the measured pulmonary artery pressure is approximately equal to left atrial pressure
What does the P wave on an EKG represent?
Atrial depolarization
Does NOT include atrial repolarization; this is buried in the QRS complex
What does the PR interval on an EKG represent?
Conduction velocity/time through the AV node
There is an increase in the PR interval if there is a AV nodal block
How does autonomic stimulation affect the duration of the PR interval?
Sympathetic stimulation decreases the interval by increasing conduction velocity
Parasympathetic stimulation increases the interval
What does the QRS complex on an EKG represent?
Depolarization of the ventricles
What does the QT interval on an EKG represent?
The entire period of depolarization and repolarization of the ventricles
What does the ST segment on an EK represent?
The period where the ventricles are depolarized
This segment is (or should be) isoelectric
What does the T wave on an EKG represent?
Ventricular repolarization
What ion determines the resting membrane potential of the cardiac tissue?
K
Em is determined by K conductance, and approaches Ek
What effect does inward current have upon the cardiac membrane potential?
Inward current brings positive charge into the cell
This depolarizes the membrane potential
What effect does outward current have upon the cardiac membrane potential?
This causes positive charge to leave the cell
Hyperpolarization of the membrane potential
What maintains the ionic gradient across the cardiac cell membrane?
Na-K ATPase
What are the phases of a cardiac action potential?
Phase 0: upstroke/depolarization
Phase 1: brief period of repolarization
Phase 2: plateau
Phase 3: repolarization
Phase 4: resting membrane potential
What causes phase 0 (upstroke)?
There is a transient increase in Na conductance, resulting in an inward Na current that depolarizes the membrane
At the peak of the action potential, Em approaches Ena
What causes phase 1 (initial repolarization)?
There is a small outward current, due to efflux of K and a decrease in Na conductance
What causes phase 2 (plateau)?
There is a transient increase in Ca conductance
This causes an inward Ca current
This is followed by an increase in K conductance (outward K current)
Because the inward and outward currents are approximately equal, the membrane potential is stable
What causes phase 3 (repolarization)?
Ca conductance decreases
K conductance increases and therefore predominates
The high conductance results in a large outward K current (Ik) which hyperpolarizes the membrane back towards Ek
What causes phase 4 (resting membrane potential)?
The inward and outward currents (Ik1) are equal
Em approaches Ek
What part of the heart is the pacemaker?
The SA node, which exhibits unstable resting potential (automaticity)
What are the latent pacemakers of the heart?
The AV node and Purkinje fibers
These regions also exhibit automaticity and can override the SA node if it is suppressed
What is the order of the cardiac pacemakers from fastest to slowest?
SA node > AV node > Purkinje fibers
How does the phase 0 of the SA node differ from that of the rest of the heart?
It is caused by an increase in Ca conductance instead of Na
The inward Ca current drives the membrane potential toward Eca
What causes phase 3 of the SA node?
Repolarization, caused by increased K conductance that results in outward K current
This repolarizes the membrane
How does phase 3 of the SA node differ from the rest of the heart?
Repolarization is mediated by outward K current only, not outward K and inward Ca
How does phase 4 of the SA node differ from the rest of the heart?
It is a slow depolarization, not steady state/flat. This is what accounts for the automaticity of the SAN
Caused by an increase in Na conductance; the inward Na current is known as If
What turns on the If current?
Repolarization of the membrane potential
What is cardiac conduction velocity?
The time it takes for excitation to spread throughout the cardiac tissue
What determines the conduction velocity?
The size of the inward current during the upstroke of the action potential. Larger inward current = higher velocity
Where is cardiac conduction velocity fastest? Slowest?
Fastest in the Purkinje system
Slowest in the AV node
Why is conduction velocity slowest in the AV node?
This allows time for the ventricles to fill before ventricular contraction. If this duration is too short, ventricular filling may be compromised
What is cardiac excitability?
The ability of cardiac cells to initiate action potentials in response to inward, depolarizing current
It is a function of the extent to which ion channels recover such that they can carry the inward current
Does cardiac excitability change or stay constant?
It changes over the course of the action potential; this is reflected in the existence of refractory periods
What is the absolute refractory period?
The time during which no new action potential can be generated, regardless of the magnitude of the inward current
What is the effective refractory period?
The period during which a conducted action potential cannot be elicited
Seems to be the same as the absolute refractory period except slightly longer
What is the relative refractory period?
The period during which an action potential can be elicited, but a larger inward current is required
What is the duration of the relative refractory period?
Begins immediately after the absolute refractory period, when repolarization is almost complete
What is a chronotropic effect?
Produces a change in heart rate
Negative chronotropic effect decreases the heart rate by decreasing the firing frequency of the SA node
What is the structure of the cardiac sarcomere?
This is the contractile unit of the myocardial cell
Delineated as the area between two adjacent Z lines
Contains thick filaments (myosin) and thin filaments (actin, troponin, tropomyosin)
How does the cardiac sarcomere shorten?
Like in skeletal muscle, this occurs using the sliding filament model
Thin filaments slide along thick ones by forming and breaking cross-bridges between actin and myosin
What are intercalated disks?
Occur at the ends of myocardial cells
Maintain cell-cell cohesion
Contain gap junctions
What are gap junctions?
Low-resistance paths between cells that allow for rapid electrical spread of action potentials
These are responsible for the heart's behavior as an electrical syncytium
Are mitochondria more or less numerous in cardiac tissue relative to skeletal muscle?
More numerous
What are T tubules?
Contiguous with the cell membrane
They invaginate the cells at the Z lines and carry action potentials to the cell interior
Well developed in the ventricles, less developed in the atria
Form dyads in the sarcoplasmic reticulum
What is the sarcoplasmic reticulum?
Small-diameter tubules that are in close proximity to the contractile elements of the cell
Site of storage and release of Ca for excitation-contraction coupling
What is contractility?
The intrinsic ability of the heart to develop force at a given muscle length (also known as inotropism)
What determines cardiac contractility?
The intracellular Ca concentration
What index is used to estimate the contractility of the heart?
The ejection fraction, which is normally 0.55 (55%)
How does parasympathetic stimulation decrease contractility?
Decreases the force of contraction in the atria by decreasing the inward Ca current during the plateau
What factors increase the mean systemic pressure?
Increase in blood volume
Decrease in venous compliance (shift of blood into the arterial compartment)
What effect does an increased mean systemic pressure have upon the vascular function curve?
It shifts it to the right (you are increasing the pressure for a given cardiac output)
What determines the slope of the vascular function curve?
The resistance of the arterioles
What effect does decreased total peripheral resistance have upon the vascular function curve?
It decreases the slope, because when resistance decreases, there is an increase in venous return due to the vasodilation
What is the equilibrium point?
The point of intersection between the cardiac output and vascular function curves
It is where cardiac output equals venous return
How do inotropic agents change the cardiac output curve?
They increase contractility and cardiac output, so stroke volume increases
This shifts the cardiac function curve up
How do changes in blood volume or venous compliance change the vascular function curve?
Increased blood volume or decreased venous compliance both increase mean systemic pressure, which shifts the curve to the right
This increases both cardiac output and right atrial pressure
How do changes in total peripheral resistance affect the cardiac output and vascular function curves?
Increased resistance will shift the cardiac function curve down, and decrease the slope of the vascular function curve (because there is decreased venous return)
This establishes a new equilibrium point where both CO and venous return are decreased, but right atrial pressure is unchanged
What is stroke volume?
The volume ejected from the ventricle on each beat
Formula for stroke volume
SV = EDV - ESV
Formula for cardiac output
CO = SV x HR
What is the ejection fraction?
The amount of EDV that is ejected in each stroke volume
What factor determines ejection fraction?
Contractility
What is the normal value for ejection fraction?
55%
What is stroke work?
The work that the heart performs on each beat
Fatty acids are the primary energy source
Formula for stroke work
Stroke work = arterial pressure (aortic or pulmonary) x stroke volume
What factors determine cardiac oxygen consumption?
Increased afterload
Increased size of the heart
Increased contractility
Increased HR
Oxygen consumption is directly related to the amount of tension developed by the ventricles
Formula for cardiac output using the Fick principle
CO = O2 consumption / (O2 conc in pulmonary vein - O2 conc in pulmonary artery)
What does it mean for a phase of the cardiac cycle to be isovolumetric?
All valves are closed so there is no change in volume
How does atrial systole related to ventricular filling?
It contributes to ventricular filling, but is not essential
What produces the fourth heart sound?
Filling of the ventricle by atrial systole
This sound is not audible in normal adults
What produces the first heart sound?
Closure of the AV valves at the onset of isovolumetric ventricular contraction
Why might the first heart sound be split?
The mitral valve closes before the tricuspid valve
What are the periods of ventricular ejection?
Rapid ventricular ejection
Reduced ventricular ejection
When is most of the stroke volume ejected?
The rapid ventricular ejection
When do the atria begin filling?
During rapid ventricular ejection
What is the difference between rapid and reduced ventricular ejection?
During reduced ejection, the ejection is slower and ventricular pressure begins to decrease
What produces the second heart sound?
Closure of the semilunar valves
What causes the second heart sound to be split?
Inspiration
What is the "blip" in the aortic pressure tracing of the cardiac cycle after the closure of the aortic valve?
The dicrotic notch or incisura
What produces the third heart sound?
Rapid blood flow from the atria into the ventricles
Normal in children, but associated with disease in adults
Where are the baroreceptors located?
These stretch receptors are found in the walls of the carotid sinus and in the aortic arch
How does the baroreceptor reflex work?
Decreased arterial pressure results in decreased stretch
This decreases the firing rate of the carotid sinus nerve
Information is carried to the vasomotor center in the brainstem
The vasomotor center decreases vagal stimulation and increases sympathetic outflow
This will: increase heart rate, increase contractility and stroke volume, and vasoconstrict the arterioles and veins (this increases venous return and increases cardiac output)
How is the Valsalva maneuver used to demonstrate the baroreceptor mechanism?
You are expiring against a closed glottis
This increases intrathoracic pressure and decreases venous return
If the baroreceptor reflex is intact, you will increase the heart rate
What is the purpose of the RAS?
Adjustment of blood volume
What is the first enzyme to come into play in the RAS?
Renin -- cleaves angiotensinogen to angiotensin I
What is the physiologically active compound in the RAS?
Angiotensin II
What degrades angiotensin II?
Angiotensinase
What are the steps of the RAS?
There is a decrease in renal perfusion pressure
Juxtaglomerular cells in the afferent arteriole produce renin
Renin cleaves angiotensinogen to angiotensin I
Angiotensin I goes to the lungs and is cleaved by ACE to give angiotensin II
What is the mechanism of ACE inhibitors?
ACE inhibitors block the conversion of angiotensin I to angiotensin II
This decreases blood pressure
What is Captopril?
An ACE inhibitor
What do AT1 antagonists do?
They block the angiotensin receptor to prevent angiotensin II from exerting effects
This decreases blood pressure
What is Losartan?
An AT1 antagonist
What are the effects of angiotensin II?
Stimulation of the synthesis and secretion of aldosterone
Increases Na-H exchange in the proximal convoluted tubule of the nephron (leads to contraction alkalosis)
Increases thirst
Vasoconstricts the arterioles, increasing resistance and arterial pressure
Where is aldosterone produced?
The adrenal cortex
What does aldosterone do?
Increases Na reabsorption in the distal tubule of the nephron -- increases ECF volume, blood volume, and arterial pressure
Is the action of aldosterone fast or slow?
Slow, because it requires new protein synthesis
How does the chemoreceptor reflex work?
When the brain is ischemic, PCO2 in the CSF increases
Chemoreceptors in the vasomotor center increase sympathetic outflow
This causes vasoconstriction to divert blood flow away from peripheral organs and toward the heart
The arterial pressure increases to preserve oxygenation of the brain
Note that this reflex can be sustained to life-threatening levels
What is the Cushing reaction?
Increased intracranial pressure compresses the cerebral blood vessels
This leads to cerebral ischemia and increased cerebral PCO2
The vasomotor center increases sympathetic outflow
This increases arterial pressure
Where are the peripheral chemoreceptors located?
The carotid and aortic bodies
What are chemoreceptors sensitive to?
Decreases in PO2
Under what physiological conditions does vasopressin come into play?
Regulation of blood pressure in response to hemorrhage
Not involved in minute-to-minute regulation of normal blood pressure
What is another name for vasopressin?
Antidiuretic hormone (ADH)
What causes vasopressin to be released?
Atrial receptors respond to decreased blood volume or decreased blood pressure
Vasopressin is released from the posterior pituitary
How does vasopressin increase low blood pressure toward normal?
Vasoconstriction via activation of V1 receptors on arterioles
Increases water reabsorption in the renal tubule via activation of V2 receptors
What conditions cause ANP to be produced?
Released from the atria in response to increased blood volume and atrial pressure
What are the effects of ANP?
Vasodilation
Increases excretion of Na and water
Inhibits renin secretion
What structure is found at the junction of the arterioles and the capillaries?
Precapillary sphincters
These are bands of smooth muscle
What is the purpose of precapillary sphincters?
Blood flow through the capillaries is regulation by constriction and dilation of these sphincters
How do lipid-soluble substances cross the capillary wall?
Simple diffusion
How do O2 and CO2 cross the capillary wall?
Simple diffusion
How do small water-soluble substances cross the capillary wall?
They use the water-filled pores between endothelial cells
Proteins are generally too large to cross by this mechanism
How do water, glucose, and amino acids cross the capillary wall?
Endothelial pores
What is unusual about the capillary endothelium in the brain?
The pores between endothelial cells are exceptionally tight
This gives rise to the integrity of the blood-brain barrier
What is unusual about the capillary endothelium of the liver and intestine?
The pores are unusually wide and allow passage of protein
What are sinusoids?
Capillaries in the liver and intestines
These capillaries have unusually wide fenestrations that permit passage of proteins
How do large water-soluble substances cross the capillary wall?
Pinocytosis
Formula for the Starling equation
J = Kf[(Pc - Pi) - (PIc - PIi)]
J = fluid movement
Kf = hydraulic conductance
P = hydrostatic pressure of the capillary and interstitium
PI = colloid osmotic pressure of the capillary and interstitium
What does the sign of J indicate in the Starling equation?
If J is positive, there is net fluid movement out of the capillary (filtration)
When J is negative, there is net fluid movement into the capillary (absorption)
What is the significance of Kf?
It is the hydraulic conductance (water permeability) of the capillary wall
What determines the hydrostatic pressure of the capillary?
Arterial and venous pressures and resistances
How does hydrostatic pressure change along the length of the capillary?
It is highest at the arteriolar end and lower at the venous end (except for glomerular capillaries, where it is nearly constant)
What determines the colloid osmotic pressure of the capillary?
Protein concentration in the blood
Dehydration increases concentration, nephrotic syndrome, protein malnutrition, and liver failure decrease concentration
What increases the colloid osmotic pressure of the interstitium?
Inadequate lymphatic function
What is the function of lymph?
Collection of excess filtered fluid from the capillaries
This fluid is returned to circulation
Any filtered proteins are also returned to circulation
How does lymph flow?
It is unidirectional
One-way flap valves allow interstitium fluid to enter the lymph vessels, but that fluid is unable to leave
One-way valves and skeletal muscle contractions aid in the unidirectionality of flow
What is edema and how does it develop?
Edema occurs when the volume of interstitial fluid exceeds the capacity of the lymphatics to return fluid to circulation
Can be caused by excess filtration or blocked lymphatics
What is endothelium-derived relaxing factor?
Produced by endothelial cells and causes vasodilation via cGMP
One form of EDRF is nitric oxide
How does circulating ACh cause vasodilation?
It stimulates the production of nitric oxide in vascular smooth muscle
What is autoregulation?
Blood flow to an organ remains constant over a wide range of perfusion pressures
What organs exhibit autoregulation
Heart
Brain
Kidneys
If the perfusion pressure to the heart suddenly decreased, what would be the autoregulatory response?
Vasodilation of the arterioles to maintain constant blood flow
What is active hyperemia?
When the blood flow to an organ is proportional to its metabolic flow
What is reactive hyperemia?
When blood flow to an organ increases after a period of occlusion
The longer the occlusion lasts, the greater the increase in blood flow above pre-occlusion levels
What is the myogenic response?
Vascular smooth muscle contracts when it is stretched
When there is increased perfusion, vasoconstriction increases resistance to maintain constant blood flow
What is the metabolic hypothesis?
Tissue supply of oxygen is matched to the tissue's demand for oxygen
Vasodilator metabolites are produced in response to metabolic activity?
What are some vasodilatory metabolites?
CO2
H
K
Lactate
Adenosine
Is sympathetic innervation of vascular smooth muscle constant in all tissues?
No
Skin has the most sympathetic innervation in the vasculature
Coronary, pulmonary, and cerebral circulations have the least innervation
How does histamine affect vasoactivity?
Arteriolar dilation
Venous constriction
This results in increased capillary hydrostatic pressure, which can increase filtration and cause local edema
What stimulates histamine release?
Tissue trauma
How does bradykinin affect vasoactivity
Arteriolar dilation
Venous constriction
Increased capillary hydrostatic pressure favors filtration and can result in edema
How does serotonin (5-hydroxytryptamine) affect vasoactivity?
Arteriolar constriction
What stimulates serotonin release?
Blood vessel damage
This helps to prevent blood loss
What vasoactive substance has been implicated in the genesis of migraines?
Serotonin
Thought to potentially cause vascular spasms
Which prostaglandins are vasodilators?
Prostacyclin (PGI2)
E-series PGs (PGE family)
Which prostaglandins are vasoconstrictors?
F-series PGs (PGF family)
Thromboxane A2
What is primarily responsible for regulation of coronary circulation?
Local metabolic factors
Hypoxia and adenosine are the most important
What is primarily responsible for cerebral circulation?
Local metabolic factors
CO2 is an important local vasodilator
Vasoactive substances in the systemic circulation have little effect because they are excluded by the blood-brain barrier
What controls the vasoactivity of arterioles in the skeletal muscle?
Sympathetic innervation
Local metabolic factors
How does sympathetic stimulation affect vasoactivity in the skeletal muscle?
Sympathetic innervation is the primary regulator of resting tone
Stimulation of alpha 1 receptors causes vasoconstriction
Stimulation of beta 2 receptors vauses vasodilation
How do metabolic factors affect vasoactivity in the skeletal muscle?
During exercise, when oxygen demand is high, metabolic factors are the primary determinant of vascular tone
Important metabolic vasodilators are lactate, adenosine, and K
How does exercise cause reactive hyperemia?
Muscular contractions compress the arteries and decrease blood flow
In the post-occlusion period, reactive hyperemia increases blood flow to replenish the oxygen deficit
What controls the vasoactivity of blood flow in the skin?
Sympathetic activity -- contribute to temperature regulation
How does temperature regulation in the skin work?
High ambient temperature causes cutaneous vasodilation, which allows excess body heat to dissipate
What is the "triple response" in the skin?
The triple response is how skin responds to trauma
A red LINE is produced
A red FLARE is produced
A WHEAL is produced
What is a wheal?
Local edema resulting from histamine release, which increases capillary filtration
What happens to the various indices of cardiovascular function when you go from a supine to a standing position?
Blood pools in the lower extremities because of the high venous compliance
This increases Pc in the legs and fluid is filtered into the interstitium (possibly causing edema)
Blood volume and venous return decrease
Decreased venous return decreases stroke volume and cardiac output
Low cardiac output decreases arterial pressure (can cause fainting)
Compensatory mechanisms attempt to increase blood pressure to normal via the baroreceptor reflex
What is the compensatory mechanism when you go from a supine to a standing position?
Carotid sinus baroreceptors detect decreased arterial pressure
Firing rate of the carotid sinus nerves decreases
Increased sympathetic outflow from the vasomotor center
What is orthostatic hypotension and what causes it?
It is when you experience fainting or light-headedness upon standing
Happens in people with an impaired baroreceptor reflex (such as people being treated with sympatholytic agents)
What happens when you hemorrhage?
Decreased blood volume decreases cardiac output and arterial pressure
Carotid sinus baroreceptors detect decreased pressure
Increased sympathetic outflow and decreased parasympathetic outflow
Peripheral chemoreceptors detect hypoxia and supplement the baroreceptor mechanism by increasing sympathetic outflow
Cerebral ischemia increases PCO2, which activates central chemoreceptors to increase sympathetic outflow
Arteriolar vasoconstriction, which decreases Pc and favors capillary reabsorption
Adrenal medulla releases epinephrine and norepinephrine
RAS is activated by decreased renal perfusion pressure
ADH is released