Circulation, Hemodynamics Flashcards
Smaller vessels that go from arteries to organs
Arterioles
Small vessels that go from arterioles and drain into venules
Capillaries
Place where all exchange between blood and tissue occurs
Capillary beds
Small vessels that drain from capillary beds into larger veins
Venules
How is flow measured?
Liters/min
Pressure gradient/resistance
= flow
If pressure is high, flow is…
Faster
If resistance is high, flow is
Slower
2 things that influence vascular resistance
1) blood viscosity
2) radius of vessel
What causes high viscosity in blood
High hematocrit (high level of RBCs)
The smaller the radius of a vessel the __________ the resistance
Higher
If radius of vessel 1 is X and vessel 2 is 2X, how much more is flow of vessel 2?
16 times
What determines distribution of blood
Metabolic demand
True/False: we have a finite volume of blood
True
Vessels with large elaborate walls
Arteries
2 functions of arteries
1) fast transportation of blood from heart to tissue
2) store pressure for flow when heart at rest
5 parts of arterial wall
1) endothelial cells
2) connective tissue (collagen/elastin)
3) smooth muscle
4) sympathetic nerves
5) external connective tissue with tiny vessels
What is force of blood against arterial wall?
Arterial BP
What is systolic pressure
Ventricular contraction
What is diastolic pressure
Resting pressure in arteries (ventricular diastole)
2 purposes of reading arterial BP
1) health of vessel walls
2) blood volume
What is Pulse Pressure
Systolic - Diastolic
How do you calculate MAP
diastolic + 1/3 pulse pressure (sys - dias)
What is the average BP at all times called?
Mean Arterial Pressure (MAP)
True/False: MAP is not a straightforward measure
True
What are taps heard during BP cuff reading called
Korotkoff sounds
If you drop BP cuff pressure too fast, what happens?
Underestimated Systolic
What is made of mostly endothelium wrapped in smooth muscle
Arterioles
Is the diameter of an arteriole changeable?
Yes
What vessel is the “Gatekeeper to organs”
Arterioles
2 main functions of Arterioles
1) distribute blood based on metabolic demands
2) regulate arterial BP
What is a change in arteriole diameter by constricting or dilating called
Arteriole tone
How is normal arteriole tone determined (4 factors)
1) elasticity
2) sympathetic input
3) hormones
4) blood volume
Vasoconstriction does what to flow?
Decreases
What does vasodilation do to flow?
Increases
2 general categories that cause vasoconstriction or vasodilation
1) intrinsic
2) extrinsic
What causes intrinsic changes in vasodilation or vasoconstriction
Local factors
What is meant by “local factors”
A change in the tissue
2 subcategories of local control
1) chemical
2) physical
What is the most important local chemical change that is based on organ workload
Local metabolic change
What causes another local chemical change in arterioles
Histamine release
2 causes of local physical control to arterioles
1) heat/cold (local application)
2) myogenic response to stretch
During local metabolic change in arterioles, what senses change in O2, CO2, acidity, Adenosine
Endothelial cells
What do endothelial cells release in response to a metabolic change in arterioles
1) Endothelin
2) nitric oxide
What does endothelin do in vessel?
Constricts (conserves blood)
What does nitric oxide do?
Dilated to increase blood flow
What is the most important extrinsic control of arterioles
Sympathetic effect
If sympathetic effect is increased, what happens to arterioles
General Vasoconstriction
If sympathetic is decreased, what happens
Vasodilation
Sympathetic nerve fibers supply areteriole smooth muscle everywhere except where?
The brain
What is TPR
Total peripheral (vascular) resistance
What influences TPR the most?
Arteriole diameter
MAP is like __________ pressure in a pipe
Constant
If MAP is constant pressure in a pipe, what act as spigots to change resistance?
Arterioles
What does epinephrine do to arteriole?
Dilates
What does norepinephrine do to arterioles?
Constricts
What do vasopressin and angiotensin 2 do?
Constrict
What gets majority of blood distribution when at rest?
Digestive and liver (27%)
What gets majority of blood distribution with moderate exercise
Skeletal muscle and heart
During exercise, sympathetic vasoconstricts everywhere except where?
Skeletal muscle and heart
If tissue mass increases, what happens to capillary density
It will increase too
What is velocity of blood in capillaries
Slow
True/false: decrease in velocity of capillary does not change flow rate
True
What is capillary made of
Endothelial cells
Is a capillary diameter slightly less or more than the diameter of a RBC?
Less
What moves freely through capillary pores?
1) fluid and small h2o soluble substances
2) polar substances (electrolytes)
3) lipid soluble proteins
What can’t get through capillary pores?
Plasma protein (albumen) and rbc/wbc
What do large water soluble substances need to pass thru capillary pores?
Active transport via vesicles
What flows to low concentration gradients in capillaries
O2 in tissue
CO2 out of tissue
NA, K, glucose
What sit between arterioles and venules
Capillary beds
What are slightly larger than capillaries
Metarterioles
What acts as a freeway between arterioles to venules
Metarterioles
What controls blood flow through capillary beds
Pre capillary sphincters
If pre capillary sphincters are contracted, where does blood flow
Metarterioles
If pre capillary sphincters are relaxed, where does blood flow
Capillaries
What controls the contraction or relaxation of the precapillary sphincters?
Metabolic needs
If there’s a high metabolic need, what does the precapillary sphincter do?
Relaxes and delivers O2, etc to tissue
What kind of process is distribution of fluid across capillaries
Passive
What distributes ECF between vascular compartment and interstitial compartment
Capillary bulk flow
What can capillary bulk flow buffer in a small way
Blood pressure
Hydrostatic
Pushes
Oncotic
Pulls
What does capillary hydrostatic BP favor?
Filtration
If blood volume is low and BP is low, what will capillary BP do?
Reabsorb
What are 2 constant passive pressures that reabsorb?
Capillary Oncotic
Interstitial hydrostatic
Pulls fluid into capillary
Capillary Oncotic
Pushes against capillary wall from outside
Interstitial hydrostatic
What would only happen if albumen leaked outside of capillary wall and pull fluid to interstitial space?
Interstitial Oncotic
If BP and blood volume is high, what would capillary BP do
Ultrafiltration
Large vessels with endothelial lining and very little smooth muscle
Veins
What are also called Blood Reservoirs or Capacitance Vessels?
Veins
At rest, what % of systemic blood volume is in systemic veins?
64%
During time of stress (exercise) what do veins do to send systemic blood volume to heart
Constrict
Venous return from vasoconstriction pushes blood to the heart which does what to End Diastolic Volume and Stroke Volume?
Increases
What is the volume of blood the veins can accommodate?
Venous capacity
What is the volume of blood entering each atrium from venous vessels
Venous return
What in veins prevents backflow
Valves
What are 3 “push” factors that influence venous blood return?
1) sympathetic vasoconstriction
2) muscles
3) valves
What are 2 “pull” factors that influence venous return to heart?
1) less thoracic pressure
2) cardiac suction
Measurement that tells amount of resistance in arteries
TPR
what affects TPR
1) blood viscosity
2) arterial radius
Short term control of MAP
1) Baroreceptor reflex (HR)
2) sympathetic/parasympathetic (TPR)
Where are baroreceptors found
Aortic arch
Carotid sinus
What do baroreceptors do
Measure stretch on artery wall
T/F: Baroreceptors are only good for a few minutes
True
What extrinsic influences arterial radius
Epi and vasopressin
What is long term control of MAP
Kidneys. Regulates fluid/plasma
