Arteriol Vasculature

Question 1

Three layers of artery

Answer 1

1. tunica intima (inner)
   - endothelium
   - one cell layer thick
   - paracrine functions
   - only in small arteries
2. tunica media
   - variable number of cell layers thick
   - contains EC matrix, elastin, collagen
   - contains smooth muscle cells
3. tunica adventitia
   - site of sympathetic nerves
   - “vaso vasorum” provides blood to smooth muscle (b/c blood vessel too thick)
   - extensive EC matrix

Question 2

What vessels have largest cross sections area vs what vessels have largest aggregate cross sectional area

Answer 2

CSA- aorta
Aggregate CSA- capillaries (narrow vessels but there are so many)

Question 3

What vessels have the slowest velocity

Answer 3

Capillaries
Slowest to allow for gas exchange. Also small radius so high resistance

Question 4

What can increase cross sectional area, why?

Answer 4

Branching
Total CSA of daughter vessels > parent vessels

Question 5

How is velocity related to CSA

Answer 5

Velocity is inversely related to CSA
- Insufficient gas exchange if velocity too high

Question 6

What is hemodynamics

Answer 6

Physical study of blood flow and the vessels it flows through

Question 7

Hemodynamics: what is the velocity equation

Answer 7

V = Q (flow)/A (CSA)
Velocity refers to the linear velocity of RBC through tube

Question 8

What is Q

Answer 8

Q= flow, the volume of fluid moving through the vessel per unit time

Question 9

How does the value of flow change in a single vessel

Answer 9

Q= constant
If area changes, velocity also changes
V= Q/A

Question 10

When does blood flow faster or slower in vessels, based on area

Answer 10

Velocity is slower in wider vessels
Velocity is faster in narrower vessels

Question 11

What is the hemodynamic equivalent to ohm’s law

Answer 11

P=QR
Pressure- driving force between two points (change p)
Resistance-R most important variable that controls flow

Question 12

What variable has the most control over flow

Answer 12

Resistance
P=QR

Question 13

What Determines resistance

Answer 13

1. Poiseuille’s Law (R=8nL/pi*r^4)
2. Arrangement of blood vessels (series or parallel)

Question 14

What is Poiseuille’s Law. Name variables and which variable has largest impact on resistance

Answer 14

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)

Question 15

How can the radius of vessels be affected

Answer 15

Nerves, hormones, paracrine, metabolites

Question 16

How does flow change if radius of vessel increases by x2

Answer 16

If radius x2 then resistance decreases x16 (1/r^4) -Poiseuille
Q= P/R so Q will increase by 16

Question 17

Resistance in series

Answer 17

R total= R1 + R2 + R3 (a section of the vessel will limit blood flow- dependent system)

Question 18

Resistance in parallel

Answer 18

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

Question 19

What does high compliance mean

Answer 19

1. High compliance implies high distensibility (stretchy)
   - a large volume change for a given pressure change
2. High compliance decreases pulsatility of flow (reduce pulse pressure)
   - vessel wall absorbs the cardiac pulse wave (ex. Aorta absorb)

Question 20

Compliance equation

Answer 20

Compliance - change in volume/change in pressure

Question 21

What vessel has the highest compliance

Answer 21

Aorta
-absorb part of the cardiac pulse wave-dec pulsatility. (Turbulence= dicrotic notch)
-high distensibility (stretchy) because large SV for given pressure change

Question 22

Why is decreasing pulsatility beneficial to flow

Answer 22

Allows smooth flow changes instead of blood coming out in bursts, allows Q to never be zero even during diastole

Question 23

When does compliance decrease and what does it cause

Answer 23

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