Vascular physiology Flashcards
Why is diffusion inadequate for delivering solutes to cells of large organisms?
Diffusive distance too large so substsantial diffusive delay
What is the limit for an organisms size that can be served by diffusion only?
100 microns
What influences diffusion time?
Distance travelled squared is proportional
Describe curve of distance vs diffusion time graph
Flat then exponential beyond 1mm
What is bulk flow?
Movement of medium and the solutes it contains
What does bulk flow distribute?
Substrates, waste products, signals e.g. hormones, heat and pressure
What is the benefit of bulk flow?
Overcomes diffusional limitations and works over long distances
How do you work out time for transport of bulk flow?
Distance travelled/velocity
What is the velocity of bulk flow?
2m/sec
Describe curve for distance vs time required for bulk flow
Linear through origin
What enhances bulk flow?
Reduced resistance, therefore, wide tubes and low fluid viscosity
Why is left side of heart generating 6 times the pressure of right side?
Systemic circulation is 6 times greater in resistance than pulmonary, as the resistance is 6x higher, so to keep same flow, need 6x higher pressure
In a single pump system, what happens as distance from source increases?
Lose energy, mean pressure falls and downstream tissues perfused at lower pressure
Describe the curve for blood velocity
Greatest in arteries, decreases going through arterioles and lowest in capillaries, then increases again in veins
What is blood velocity through blood vessels inversely proportional to?
Cross sectional area of vessel
i.e. capillaries have greatest cross sectional area and lowest blood velosity
Which vessels hold the most blood and why?
Veins, they are the most compliant
Describe the proportion of blood held in different vessels
Vein 70% Systemic Artery <10% Systemic capillaries <5% Lungs 10% (Note 10% in heart)
How does flow remain the same throughout circulation through different vessels?
Decrease in velocity as you branch into capillaries but cross sectional area increases so flow (velocity x cross sectional area) constant through circulation
How is flow calculated?
Change in volume/time (L/min)
Cardiac output is an example of
Flow
Example of conservation of flow
Flow in systemic circulation = flow in pulmonary circulation
i.e. larger volume in systemic circulation but circulation takes longer
What happens if there isnt conservation of flow?
Blood pools in either circuit
What happens to flow as cross sectional area increases by factor of 3, why?
Velocity decreases by 3, flow stays the same
Equation for pressure
Pressure = force/area
What happens to pressure as distance from heart increases?
Fluctuations in pressure decrease from aorta to arterioles and stop in capillaries and veins
Pressure gradually decreases (50mmHg in arterioles and 20mmHg in capillaries)
Where is the pressure constant (which vessels don’t have pulsatile flow)?
Capillaries and veins
Equation for compliance
Change in volume over change in pressure
What is the relationship between vessel radius and resistance to flow?
Doubling radius increases resistance to flow by 2^4 I.e. 16
What are the units for blood pressure?
mmHg
How do you work out pulse pressure?
Systolic bp - diastolic bp
What is normal pulse pressure?
40mmHg
What is normal mean arterial pressure?
70-110mmhg (93mmHg)
Compare pulse pressure in stiff and normal arteries, why is it like this
Smaller pressure differences as stroke volume increases in normal artery (vessels more elastic)
But: stiffer arteries, greater extremes of pressure
What is the central venous pressure?
Blood pressure in the vena cavae near right atrium of heart (reflects amount of blood returning to heart + ability of heart to pump blood back into arterial system
What is normal CVP?
5mmHg
How is CVP measured?
JVP provides indirect measure of CVP:
Patient lies at 45degrees Filling level (height of column of blood) of external jugular vein determined
What is JVP?
Pressure in the jugular vein
Describe normal stroke volume and heart rate at rest
70ml and 70bpm
What is the relationship between arterial and venous pressure, cardiac output and total peripheral resistance?
MAP-CVP=CO x TPR
What is normal cardiac output?
5l /min
Describe what we use sphygmomanometer for?
To measure blood pressure, the cuff is placed around the bare and stretched out upper arm, and inflated until pressure exceeds systolic pressure. Then the air is slowly let out of the cuff.
As soon as the air pressure in the cuff falls below the systolic blood pressure in the brachial artery, blood will start to flow through the arm once again. This creates a pounding sound when the arteries close again and the walls of the vessels hit each other after a heart beat (in diastole).
The sound can be heard by placing the stethoscope close to the elbow. Right when you start to hear this pounding for the first time you can read your systolic blood pressure off the pressure meter.
The pounding sound stops when the air pressure in the cuff falls below the diastolic blood pressure in the brachial artery. Then the blood vessels remain open. Right when the pounding stops, you can read the diastolic blood pressure off the pressure meter.
What causes k sounds?
Blood flows in spurts as pressure in artery greater than cuff pressure then drops below cuff pressure causing turbulence and K sound.
Compare and contrast the volume vs pressure (i.e. compliance) curves for veins and arteries
Both linear lines through origin
Veins line steeper as they are are complaint
Which vessels show the greatest resistance to flow?
Arterioles, causes blood to experience greatest drop in pressure.
Describe relationship between viscosity and haematocrit
Linear
Why is there not a linear relationship between viscosity and radius?
In microcirculation resistance is reduced as RBCs pass through in single file through low viscosity plasma stream,
How does viscosity affect blood flow?
Viscosity increases, TPR increases, and blood flow decreases. (Inversely proportional between haematocrit and blood flow)
Is pressure and flow linear relationship in vessels, why?
No, compliant vessels
True of false, arterioles are first sight of vascular resistance
False, aorta albeit small resistance
How does CVP change in the respiratory cycle?
Increases in respiration decreases in exhalation.
Why do arteries need a thicker wall?
Greater tension needed to exert on blood to deal with greater pressure
Mean systemic arterial pressure at the level of the heart, in a healthy individual at rest, is …
95 mm Hg (13 kPa)
Cardiac output may be acutely increased by…
A fall of total peripheral vascular resistance
A rise in blood haematocrit would increase peripheral vascular resistance?
True
A competitive antagonist of alpha1 adrenoceptors?
Prazosin
