Vascular Phys Flashcards
Circulatory nutrient delivery
rapid delivery to within 10-20 micrometers of most cells
Circulatory Functions
- Nutrient & waste exchange
- Electrolyte & H2O balance
- Body temp regulation
- Delivery of hormones
- Delivery of defense mechanisms
Microcirculation consists of
arterioles, capillaries, venules
Microcirculation location
within organs
arterioles =
stopcock of organ blood flow
Veins are
reservoir of blood in the body
What happens when veins constrict?
there is an increase in venous return
% Total Blood Volume in Pulmonic Circulation
9%
% Total Blood Volume in Systemic Circulation
84%
% Total Blood Volume in Heart
7%
Cardiac Output Redistributed for Changes in Metabolic Demands based on..
reconditioning and non-reconditioning organs
Reconditioning Organs
have role in “reconditioning” blood to improve it for entire body
ex: GI tract, Kidneys,
amount of blood received by reconditioning organs
more blood than necessary for metabolic needs
Reconditioning organs can..
tolerate reduction in blood flow when need be because they get more than needed
Non-reconditioning Organs
ONLY receive exact amount of blood they need to live
ex: brain, heart, skeletal muscle, bone
Hemodynamics
study of physical factors that determine blood flow & blood pressure in the body
Physical Factors of Hemodynamics
pressure, velocity, flow, resistance, diameter, velocity
Systemic Pressure
high pressure
pulsatile blood pressure
increase and decrease of artery blood pressure (125/80)
pulsatile blood pressure in arteries
occurs because of cardiac systole
pulsatile blood pressure in capillary beds is based on:
- Distensibility of large arteries
2. Frictional resistance of small arteries & arterioles
Why is pulsatile blood pressure in capillaries important?
It provides constant movement & supply of blood in organs & allows for constant exchange.
Pulmonic pressure
low pressure
Why is pulmonic pressure low pressure?
less resistance to overcome (shorter tube length)
Why do you want a low pressure in pulmonic circulation?
high pressure would drive fluid out of capillary beds & into the lung tissue
PVR (Pulmonary Vascular Resistance)
sum of resistance of vasculature in pulmonary circulation
SVR (Systemic Vascular Resistance)
sum of resistance of vasculature in systemic circulation
PVR compared to SVR
PVR ««< SVR
Velocity of blood
varies inversely as a function of cross-sectional area (CSA)
What happens if CSA increases?
Velocity decreases & get maximal exchange in capillaries
What happens if CSA decreases?
velocity increases and amount exchanged decreases
Vena Cava velocity vs. aorta velocity
vena cava’s velocity is lower than aorta because it’s a bit larger than the aorta
Flow through all levels of circulation
constant
Flow velocity varies
as a function of CSA of each level
Flow Velocity =
particle movement (distance) per unit time
Flow rate
rate of displacement of volume of a fluid
Flow depends on
pressure gradient and vascular resistance
Pressure gradient is the…
primary force of blood flow
Flow is
independent of absolute/individual pressure levels
Resistance depends on
vessel radius, vessel length, and blood viscosity
Vessel Radius
changes in the body as necessary
blood viscosity
friction of molecules in blood stream
What changes to influence resistance?
vessel radius
What doesn’t change to affect resistance?
vessel length and blood viscosity
What happens if you increase vessel radius 2X?
you decrease resistance 16X & increase flow 16X
Viscosity
varies as a function of hematocrit
normal hematocrit
40% total blood volume
normal blood viscosity vs water viscosity
3x greater than water’s
If blood viscosity is 3X higher than water’s,
resistance is higher & pressure must increase 3X to push blood through vasculature
Types of Changes in Viscosity
- Anemia
2. Polycythemia
Anemia
low RBC count
anemia effects on circulation
decreases viscosity, decreases resistance, decreases pressure, increases venous return, increases cardiac output, causes hypoxia (decreased O2 delivery), which increases CO more,
What happens if you’re anemic and CO can’t keep up with metabolic needs?
heart failure… death!
Polycythemia
high RBC count
Polycythemia’s effect on blood
increases viscosity, increases resistance, increases pressure, decreases flow, decreases venous return, increases blood volume
increased blood volume in polycythemia
offsets the decrease in venous return caused by polycythemia which maintains normal CO
Vessel Arrangements
- Parallel
2. Serial
Parallel Vessel Arrangements
occurs in most systemic vascular beds
Parallel Vessel Arrangement affect on Resistance
Total R < R of individual component in parallel arrangement
benefits of parallel vessel arrangements
- Reduces SVR
- Blood flow is independently adjusted
- Blood flows at similar perfusion pressure
- Arterial blood is of identical composition
Significance of arterial blood being of identical composition in parallel vessel arrangements
organs see “fresh” blood. not blood that’s passed through other organs first
Serial Vessel Arrangement occurs in
splanchnic & renal beds
Serial Vessel Arrangement’s affect on resistance
high resistance
Serial Vessel Arrangement’s affect on pressure
drop in pressure gradient as you move across each bed
Patterns of Blood Flow
- Laminar
2. Turbulent
Laminar Blood Flow
- normal
- streamlined & straight
- silent
Turbulent Blood Flow
- mostly abnormal
- noisy
Turbulent blood flow used diagnostically for
- murmurs
- bruits
murmurs
cardiac valvular lesions
bruits
vessel stenosis, shunts
critical velocity
where flow switches from laminar to turbulent
Reynolds Number
measure of tendency for turbulence to occur
Example of Bruit
arteriovenous fistula (joining of artery & vein) decrease in BP => increased CO to accomodate
Turbulence is created by…
- Large vessel diameter (aorta)
- Large Vessel branch points
- High velocity (anemia)
- Obstruction (atherosclerosis)
- Low viscosity (anemia)
Turbulence frequencies
high in aorta
low in small vessels
Role of Arteries in Vascular System
to convert intermittent output of heart to steady flow into capillaries
Arteries are..
- elastic
- distribution channels
- pressure reservoirs
- contain little resistance to flow
Arterioles are…
muscular
Arterioles function
control blood flow through capillaries
arterioles’ resistance
high.
have greatest amount of R in system to control blood flow
Compliant Arteries
- in young, healthy animals
- very elastic arteries
Compliant Arteries allow
arteries to behave as pressure reservoirs (aka can swell)
Rigid Arteries are…
- in older animals
- have lost some elasticity
Rigid arteries produce
high afterlaod
Effect of rigid arteries’ loss of elasticity
loss of function as pressure reservoir in circulatory system
Flow in Rigid Arteries
stops in diastole
occurs only in systole
Flow in Compliant Arteries
continues during systole & diastole
Effect of discontinuous flow in rigid arteries
intermittent flow occurs in capillary beds, so exchange isn’t continuous
Pulse Pressure =
systolic BP - diastolic BP = SV/arterial compliance
Pulse pressure function
sharp upstroke in P (systole) -> P starts decreasing ->aortic valve shuts -> slight increase in P -> exponential decline in P (diastole) -> REPEAT
Abnormal pulse pressures
can be used diagnostically
Arteriosclerosis Pulse Pressures
high systolic P. Normal diastolic P. normal dichrotic notch
Aortic Stenosis Pulse Pressures
low, flat systolic P
normal diastolic P
no/small dichrotic notch
Patent Ductus Arteriosus Pulse Pressures
- High systolic P
- Low diastolic P
- Normal dichrotic notch
Aortic Regurgitation Pulse Pressures
- High Systolic P
- Low Diastolic P
- No dichrotic notch
Primary job of heart
control MAP
Barrow reflex starts when
MAP decreases
Effect of Barrow Reflex Starting
Increases CO, Increased systolic P
thereby maintaining normal BP
Arterioles Job
control blood flow in capillaries
Arterioles provide ___ resistance
greatest resistance to control flow
Arterioles control of resistance
independently control resistance by smooth muscle contraction
Why is independent control of R important for arterioles?
It permits arterioles to have precise control of flow into individual capillary beds & aids in BP regulation
Result of constricting arterioles
increase MAP upstream
decrease MAP downstream
Result of dilating arterioles
Decrease MAP upstream
Increase MAP downstream
basal tone
allows dilation under basal conditions & maintains BP
How does basal tone work?
- Myogenic stretch
2. Basal Norep. release
Myogenic stretch
stretch Ca channels open & increase cytosolic [Ca]
Opening of stretch Ca channels occurs
when P is put on walls, & the walls stretch
Why does more cytosolic [Ca] increase basal tone?
Ca is essential for smooth muscle contraction
Basal norep. release occurs
at sympathetic nerve fibers
Basal norep. binds
to adrenergic receptors & leads to vessel contraction/constriction
Independent Arteriolar Control caused by
systemic and local factors
Extrinsic Control/Systemic Responses done by:
- Neural influence (sympathetic N.S.)
2. Humoral Factors
Job of Extrinsic Control/Systemic Responses
regulate blood pressure
Intrinsic Control/Local Control done by:
- Metabolic Factors
- Endothelium-mediated
- Myogenic Responses
- Shear stress
Job of Intrinsic Control/Local Control
determine cardiac output distribution
aka determines which organs get which blood
Intrinsic Control/Local Control regulates:
- Autoregulation
2. Reactive Hyperemia
Metabolic Factors are important in
brain, heart, skeletal muscle
Intrinsic Control vs Extrinsic Control
Intrinsic OVERRIDES extrinsic
Constriction of Arterioles caused by
sympathetic nerves stimulate smooth muscle contraction
How does sympathetic innervation cause smooth m. contraction?
- Releases norep. into neuromuscular junction
- Norep. binds to a-1 adrenergic receptors
- Ca released & contraction occurs
What happens if you increase sympathetic nerve activity?
Increase norep. release => VASOCONSTRICTION => increased R => decreased flow
What happens if sympathetic nerve activity decreases?
decreases norep. release => VASODILATION => decreased R => increased flow
Exception to sympathetic nerve stimulation of smooth m. contraction
brain
Why is the brain the exception to smooth m. contraction by sympathetic nervous stimulation?
Brain has no a-1 receptors.
How do the brain’s arterioles contract?
use local mechanisms to maintain constant blood flow
Parasympathetic N.S. & Arterioles
basically has no effect
dilates arterioles in salivary glands, GI glands, & genetalia
Humoral Factors
- Norep. for a-1 receptors in most arteriolar smooth m.
- Ep. for b-2 receptors
Epinephrine for B-2 receptors Function
stimulates arterioles of heart & skeletal m. to dilate
Epinephrine =
“breaks” for cardiovascular system
How does epinephrine work?
It works with other local mechanisms to counteract a-1 constriction
Angiotensin II
potent vasoconstrictor
Vasopressin
potent vasoconstrictor
Angiotensin II & Vasopressin function
maintain amount of salt that kidneys retain by being released into blood stream
Metabolites cause…
local vasodilation
Active hyperemia
increased blood flow to highly active tissues
Reactive Hyperemia
increased flow to tissue AFTER flow is acutely blocked
How does reactive hyperemia work?
occlusion occurs & increases metabolite build up. When occlusion is released, flow increases to remove metabolites => longer removal time based on occlusion time
exercise effect
combination of occlusion & exercise increases [metabolite] => higher increase in flow
Local Vasoactive Mediators come from
endothelium
Types of local vasoactive mediators
- Vasodilators
2. Vasoconstrictors
Vasodilators
NO, prostacylin, EDHF
Vasoconstrictors
endothelin, Angiotensin II, prostaglandins
Sheer Stress
longitudinal frictional resistance between blood & vessel walls
Myogenic Mechanism
a smooth muscle phenomenon
Example of Sheer Stress mechanism
aids in increasing flow in tissues w/ increased metabolic demand by dilating vessels.
small arterioles dilate to metabolites well => increased sheer stress in small upstream aa. => NO release => dilation of small aa.
How myogenic contraction works?
changes in transmural pressure alters contractile states of arterioles
Myogenic Mechanism resulting from ^ pressure
^P => opening of stretch activated Ca channels => ^ Ca influx => ^ contraction => decreased r => decreased flow
Autoregulation of Flow
maintains normal organ flow despite changes in arterial pressure
What organs autoregulate best?
brain, heart, kidneys
Autoregulation of Flow Mediated by:
myogenic and metabolic responses
If perfusion pressure decreases,
flow decreases & therefore need to decrease R to ^ flow to normal levels
When perfusion pressure decreases what causes a decrease in R to bring flow back to normal?
sympathetic discharge
Sympathetic discharge effects
no change in pressure. arterioles dilate. Resistance decreases.
Myogenic response to decreased perfusion pressure
decreased stretch, less Ca entry, increased relaxation (DILATION)
Metabolic response to decreased perfusion pressure
increased [metabolite] => increased dilation to get more out
Increased perfusion pressure effects
increased flow meaning R needs to increase to bring flow back DOWN to normal levels
Myogenic response to increased perfusion pressure
^ stretch, ^ Ca entry, ^ contsriction, ^ R, decreased flow
Metabolic response to increased perfusion pressure
decreased [metabolite], ^ constriction to keep metabolites at normal levels in the region
