Arteriol Vasculature Flashcards
Three layers of artery
- tunica intima (inner)
- endothelium
- one cell layer thick
- paracrine functions
- only in small arteries - tunica media
- variable number of cell layers thick
- contains EC matrix, elastin, collagen
- contains smooth muscle cells - tunica adventitia
- site of sympathetic nerves
- “vaso vasorum” provides blood to smooth muscle (b/c blood vessel too thick)
- extensive EC matrix
What vessels have largest cross sections area vs what vessels have largest aggregate cross sectional area
CSA- aorta
Aggregate CSA- capillaries (narrow vessels but there are so many)
What vessels have the slowest velocity
Capillaries
Slowest to allow for gas exchange. Also small radius so high resistance
What can increase cross sectional area, why?
Branching
Total CSA of daughter vessels > parent vessels
How is velocity related to CSA
Velocity is inversely related to CSA
- Insufficient gas exchange if velocity too high
What is hemodynamics
Physical study of blood flow and the vessels it flows through
Hemodynamics: what is the velocity equation
V = Q (flow)/A (CSA)
Velocity refers to the linear velocity of RBC through tube
What is Q
Q= flow, the volume of fluid moving through the vessel per unit time
How does the value of flow change in a single vessel
Q= constant
If area changes, velocity also changes
V= Q/A
When does blood flow faster or slower in vessels, based on area
Velocity is slower in wider vessels
Velocity is faster in narrower vessels
What is the hemodynamic equivalent to ohm’s law
P=QR
Pressure- driving force between two points (change p)
Resistance-R most important variable that controls flow
What variable has the most control over flow
Resistance
P=QR
What Determines resistance
- Poiseuille’s Law (R=8nL/pi*r^4)
- Arrangement of blood vessels (series or parallel)
What is Poiseuille’s Law. Name variables and which variable has largest impact on resistance
R= 8nL/pi*r^4
n- blood viscosity (controlled by hematocrit, constant unless anemic or high altitude)
L- length of tube
r- radius (most important. Inc by 2= dec resistance by 16)
How can the radius of vessels be affected
Nerves, hormones, paracrine, metabolites
How does flow change if radius of vessel increases by x2
If radius x2 then resistance decreases x16 (1/r^4) -Poiseuille
Q= P/R so Q will increase by 16
Resistance in series
R total= R1 + R2 + R3 (a section of the vessel will limit blood flow- dependent system)
Resistance in parallel
1/Rtotal= 1/R1 + 1/R2 + 1/R3
A change in one resistance pathway does not limit blood flow since there are alternate paths of least resistance
What does high compliance mean
- High compliance implies high distensibility (stretchy)
- a large volume change for a given pressure change - High compliance decreases pulsatility of flow (reduce pulse pressure)
- vessel wall absorbs the cardiac pulse wave (ex. Aorta absorb)
Compliance equation
Compliance - change in volume/change in pressure
What vessel has the highest compliance
Aorta
-absorb part of the cardiac pulse wave-dec pulsatility. (Turbulence= dicrotic notch)
-high distensibility (stretchy) because large SV for given pressure change
Why is decreasing pulsatility beneficial to flow
Allows smooth flow changes instead of blood coming out in bursts, allows Q to never be zero even during diastole
When does compliance decrease and what does it cause
Decreases with age or smoking
1. increase pulsatility
2. Impair baroreflex function- contributes to hypertension with aging
3. Increases systolic pressure and thus afterload- increases work the heart needs to do, leads to hypertension and high blood pressure
