Exam II Circ Flashcards
In most tissue beds, blood flow is regulated in proportion to what?
Local metabolism
Consider the resistance in the following tissue beds: Coronary= .40 mmHg/ml/min Brain= .13 mmHg/ml/min Liver= .08 mmHg/ml/min Kidneys= .10 mmHg/ml/min
What is the total peripheral resistance?
Less than .08
Using the data from the previous question, which tissue bed would have the greatest flow (lowest resistance)?
Liver
In the following vessels, the flow rate is identical, which vessel is offering the greatest resistance to flow?
A. P1=50 P2=25
B. P1=70 P2=60
C. P1=80 P2=65
A. P1=50 P2=25
The greatest change in pressure = the greatest resistance (occurs in arterioles)
A broad band Doppler reading is indicative of what type of flow?
Turbulent
If a vessel with a length of 100cm has a cross-sectional area of .5cm2, and velocity of flow of 10cm/sec, and the pressure drop across that length is 10mmHg, what is the flow in that vessel?
300ml/min
.5cm2 x 10cm/sec = 5ml/sec x 60= 300ml/min
The vascular compartment with the greatest total cross-sectional area is what?
Capillaries
What are characteristics of parallel circuitry?
Independent of flow control, maximizes oxygen delivery to tissues, and decreases work load on the heart, minimizes TPR
A small change in volume producing a large change in pressure is characteristic of which vascular compartment?
Systemic arteries
Acetylcholine binding to the vascular endothelium has what effect?
Vasodilatation by causing nitric oxide release
What is the effect of sympathetic nervous stimulation on most vascular smooth muscle?
Vasoconstriction mediated by alpha receptors
During widespread sympathetic nervous system stimulation, which tissue bed would show the least increase in vascular resistance?
Lung
As a tissue becomes more active, how is blood flow to that tissue increased?
Tissue releases local vasodilators
At a given mean circulatory filling pressure what happens to venous return as central venous pressure increases?
Venous return decreases
If cardiac output is stopped, arterial pressure will be expected to fall until it equals what?
Critical closing pressure
In a healthy young adult comment about tissue flow during diastole.
Maintained by recoil of the arteries
If blood flow to a tissue doubles from 200ml/min to 400ml/min, and the AV O2 difference falls from .05ml O2/ml to .025ml O2/ml, comment on the increase in flow.
It is likely due to shunting (through the capillary beds)
What increases the plasma colloid osmotic effect by about 50%?
Negative changes on protein attracting and holding positive ions like sodium
What effects are attributed to slow breathing?
Increased resting oxygen saturation, decreased chemoreflex activation, decreased mean arterial blood pressure
What effect does decreasing velocity have on blood viscosity?
Increases
How does fibrinogen decrease blood viscosity?
Makes RBC’s more flexible
Use the following graph to answer the following questions.
\
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VR \
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0 5 10 CVP
Considering vascular function as central venous pressure increases, what happens to venous return?
What is the mean circulatory filling pressure equal to?
Decreases; 10mmHg
The chronic use of anti-inflammatory drugs could be expected to inhibit what process?
Angiogenesis
Consider the following data:
average capillary hydrostatic P = 17 mmHg
average capillary colloid osmotic P = 28 mmHg
average interstitial hydrostatic P = -2 mmHg
average interstitial colloid osmotic P = 9 mmHg
a. filtration > reabsorption b. filtration
C. Filtration = reabsorption
Net filtration = (17- -2) - (28-9) = 0
Which brainstem area is tonically active and is associated with a tonic SNS outflow?
Neurons anterolateral in the upper medulla and pons
Which substances are associated with local vasodilatation?
Adenosine, CO2, K+, histamine and lactic acid
What high-resistance microvessels control local blood flow by integrating multiple input which determines lumen diameter?
Arterioles
Compare the distensibility of the following vessels.
Vessel one: Vessel two:
Orig vol. = 20 ml Orig vol. = 10 ml
/\ vol = 1 ml /\ vol = 1 ml
/\ pressure = 2 mmHg /\ pressure = 2 mmHg
a. vessel one is more distensible than vessel two b. vessel two is more distensible than vessel one c. vessel one and vessel two are equally distensible
B. Vessel 2 is more distensible than vessel 1
V1: 1ml/(2mmHg20ml) = 1/40
V2: 1ml/(2mmHg10ml) = 1/20 (higher)
What may act at the level of the CNS in the development of hypotension?
NO and serotonin
In the kidney, how dos SNS stimulation increase angiotensin formation?
By stimulation of the JG cells to release renin
In response to a fall in systemic arterial blood pressure, what changes would be counterproductive in offsetting that fall?
Increase in ANP release
In the face of rising arterial blood pressure, what response would autoregulate both renal blood flow and glomerular filtration?
Constriction of the afferent arterioles
What effect does stimulation of baroreceptors have on sympathetic outflow?
Decreases
During systole, what is happening to baroreceptor activity?
Increasing
In the fetus, the ductus arteriosis shunts blood from the pulmonary artery to the aorta returning primarily from what vessel?
Superior vena cava
What is the function of the ductus venosus in the fetus?
Shunt blood from the umbilical vein into the inferior vena cava (bypasses liver)
In which tissue bed does SNS stimulation cause a metabolically-induced local increase in blood flow?
Heart
During exercise, what normally decreases?
VO2 and TPR
During exercise, most of the increase in cardiac output is due to which of the following?
Increase in heart rate
What is the main function of systemic circulation?
To deliver adequate oxygen and nutrients and remove CO2 and other waste from systemic tissues
True/False: Blood flow is proportional to metabolic demand.
True
What are the 4 components that make up vessels?
Endothelium, elastic tissue, smooth muscle, fibrous tissue
The aorta contains more _____, a typical artery contains more _____, while capillaries contain _____.
Elastic tissue; smooth muscle; endothelium only
What is the equation for Ohm’s Law?
V = IR
V is voltage
I is current flow
R is resistance
Ohm’s law is analogous to?
/_\ P = FR
P is pressure gradient
F is flow
R is resistance
Flow is equal to:
Velocity x Cross-sectional area
Where does the greatest resistance to flow occur?
Pre-capillary resistance vessels (arterioles, metarterioles, precapillary sphincters)
Resistance is equal to:
8nl/Pir4
n is viscosity
l is length of vessel
r is radius
Systemic circulation is predominantly a _____ circuit.
Parallel
What is the normal range of hematocrit?
38-45%
A narrow band Doppler reading indicates what type of flow?
Laminar flow
Reynold’s number describes:
The probability statement for turbulent flow (the greater the number, the greater the probability of turbulence)
If Reynold’s number (R#) is
Laminar
If R# is >3000, flow is usually:
Turbulent
Fick’s Principal describes:
Blood flow to a tissue/organ
What is distensibility?
Ability of a vessel to stretch/distend
What is compliance?
Ability of a vessel to stretch and hold volume
True/False: Systemic arteries are more compliant than veins.
False, veins are 24x more compliant
True/False: Veins are more distensible than systemic arteries.
True (8x more)
During chronic exercise, most of the increase in cardiac output is due to:
Increase in stroke volume
In the face of falling arterial blood pressure, which response would autoregulate both renal blood flow and glomerular filtration?
Dilation of the afferent arterioles
What causes the release of VEGF?
Hypoxia
What are the mechanical triggers for angiogenesis?
Hemodynamic and shear stress
What are the chemical triggers for angiogenesis?
Hypoxia and NO
What are the molecular triggers for angiogenesis?
Decreased glucose, inflammation and angiogenic growth factors
The vasoactive role of endothelium includes releasing what?
Prostacyclin, NO, and endothelin
Oxygen uptake is determined by what calculation?
O2 uptake = F x (A-V O2 difference)
What is the most common plasma protein in circulation?
Albumin
The reflection coefficient expresses:
How readily protein can cross the capillary wall
If the reflection coefficient is 0:
All colloid proteins freely cross the capillary wall
If the reflection coefficient is 1:
All colloid proteins are reflected, none cross the capillary wall
What is responsible for draining excess fluid from interstitial spaces?
Lymph capillaries
2/3 of all lymph comes from:
Liver and intestines
If cardiac output is stopped, what effects will be observed?
Arterial pressure will fall and venous pressure will rise
The equalibration pressure where arterial BP is equal to venous BP is called:
Mean circulatory filling pressure
Which brainstem area has vasodilatory effects and decreases cardiac activity?
Neurons anterolateral in the lower M.O.
Neurons in the posterolateral portions of the pons and medulla are associated with what area?
Sensory area (A2)
The sensory area of the vasomotor center receives input primarily from what cranial nerves?
CN IX and X
Baroreceptors are especially abundant in:
Carotid sinus and arch of aorta
True/False: Baroreceptors are more sensitive to changing pressure than static pressure.
True
What are specialized peritubular capillaries associated with juxtamedullary neurons?
Vasa recti
What hormones decrease renal blood flow?
Norepinephrine, epinephrine and angiotensin II
What hormones increase renal blood flow?
Prostaglandins (E & I)
The RAA system is stimulated by:
Decreased perfusion pressure, SNS stimulation, decreased NaCl delivery and hormones (thyroid & growth)
Renin is an enzyme that catalyzes the formation of _____ from _____.
Angiotensin I from angiotensinogen
The conversion of angiotensin I to angiotensin II occurs primarily in the:
Lung
What is the effect of tying off one renal artery?
Development of systemic hypertension
What is the effect of tying off a renal artery and removing a kidney?
No development of HTN or uremia
What is the effect of tying off a renal artery and removing both kidneys?
Development of both HTN and uremia
Hypertension generated by tying off a renal artery is called:
Goldblatt hypertensive model
What allows blood to bypass the lungs?
Ductus arteriosis and foramen ovale
What allows umbilical and portal blood to bypass the liver?
Ductus venosus
Blood from which source in the fetus is most saturated with oxygen?
Umbilical vein (80%)
Which tissues escape SNS vasoconstriction?
Heart, brain and lungs
Which CV endpoint decreases with exercise?
Total peripheral resistance
Extra O2 is used to:
Restore metabolite levels and metabolize lactate generated by glycolysis
True/False: Arterial pressure control is independent of both local flow and cardiac output.
True
In which vessel would velocity of flow be slowest?
Inferior vena cava
Blood flow to most tissues or organs is regulated in proportion to:
Metabolic demand
If the flow in a vessel is 20cm/sec and the cross-sectional area is .1cm2, what is the flow rate?
120ml/min
Which groups of vessels regulate blood flow to an organ?
Arterioles
What effect does fibrinogen have on the viscosity of blood?
Decreases viscosity
A broad band Doppler reading is obtained over the right carotid artery. What is the significance of this finding?
Partial occlusion
Angiogenesis can be impaired by:
Anti-inflammatory drugs
In cardiac failure, what happens to central venous pressure?
Increases
All else being equal, what effect would a decrease in TPR have on diastolic BP?
Decreased
When would venous return be stopped?
If CVP is equal to MCFP
A vessel has an original volume of 20ml. As volume is increased 5ml, pressure is increased to 2mmHg. Calculate the distensibiility.
.125
Distensibility = change in vol/change in pressure x original vol
D = 5/(2 x 20) = .125
As a tissue becomes more active, what is the primary way local blood flow increases?
Release of local vasodilators
What receptor mediates the SNS vasoconstrictor response?
Alpha
How does circulating Ach cause local dilation of vascular smooth muscle in a tissue bed?
Binds to endothelium causing release of NO
During ejection of blood, comment on baroreceptor activity.
Increasing
If blood flow to a tissue doubles, but AV O2 difference falls by 1/2, what happened?
It is likely due to shunting
If blood flow to a tissue is 400ml/min, the AO2 is .2ml O2/ml and VO2 is .1ml O2/ml, what is the O2 uptake?
40ml/min
F = 400 x (.2 - .1)
Using indicator dilution to determine cardiac output, as the duration of the curve increases, what is happening to the cardiac output?
Decreases
In the brain, how is excess plasma filtrate returned to the vascular system?
Via the arachnoid villi
What is “hydraulic filtering?”
Stretch and recoil of the arterial tree during the cardiac cycle
If one renal artery was stenotic, what would be expected?
Development of HTN and elvated angiotensin II levels
What is the mechanism by which SNS stimulation to the heart cause local vasodilation of coronary vascular smooth muscle?
Norepinephrine stimulation of cardiac cells which release adenosine
Which area of the vasomotor center is tonically active and provides basal stimulation of the SNS?
Pressor center
In response to a rise in extracellular fluid levels, which change would be counterproductive in keeping BP from rising?
Decreased arterial naturectic peptide release
In the fetus, what is the function of the ductus venosus?
Allows blood returning from placenta to bypass the liver and flow into the inferior vena cava
In the fetus, the blood that shunts through the ductus arteriosis is returning from which location?
Head
Slow breathing has been shown to decrease both systolic and diastolic BP due to:
Decreasing sympathetic activity
What will not increase venous return during exercise?
Increased central venous pressure
As total cross-sectional area decreases, what happens to the velocity of flow?
Increases
Under strong widespread SNS stimulation, which tissue bed would show the greatest increase in blood flow?
Heart
A large increase in local tissue flow due to an increase in metabolic activity is usually associated with what changes?
Vasodilation of pre-capillary resistance vessels
Which change is associated with a decrease in the viscosity of the blood?
Fahreus-Lindquist effect
True/False: Total peripheral resistance is always less than total coronary resistance.
True
