Lecture 9

Question 1

Darcy’s Law/Bulk Flow Law

Answer 1

Flow (Q) = ∆P/Resistance

Pressure = Driving pressure
-Mean arterial pressure (MAP) - Right atrial pressure

Resistance=
-Affected by Viscosity blood and radius vessels

Question 2

Poiseuille’s Law

Answer 2

-Describes how resistance to flow varies from certain elements

1) Viscosity = Direct relationship
2) Length = Direct relationship
3) Radius = Inverse relationship (By 4th power) = has greatest effect

Question 3

Resistance and radius relationship

Answer 3

-Resistance is the most sensitive to radius

-Doubling radius will increase flow to the 4^
1/r4

(Ex: Stenosis = reduces flow)

Question 4

Equation for Cardiac Output

Answer 4

-Cardiac output= flow

Cardiac output = Mean arterial pressure/Total peripheral resistance

• Increases w increased pressure
• Decreases w resistance

Question 5

Factors that affect Resistance

Answer 5

1) Viscosity –> flow
- Direct relationship

2) Hematocrit –> Total Blood volume/Packed cell volume
- Direct relationship

Question 6

Resistance:

Parallel and Series

Answer 6

Parallel:
-Supply of blood flow to various organ systems
-This arrangement reduces resistance to flow making heart be more efficient
-Capillary bed arrangement
1/Rt= 1/R1 + 1/R2

Series:
-Blood vessels within each organ
1/Rt=R1+R2+R3…

Question 7

Compare the Resistance of Arterioles and capillaries

Answer 7

• Arterioles are the region of greatest pressure drop/resistance
• Capillaries are smaller individually (larger resistance individually), but do not have larger resistance bc they are arranged in parallel in capillary bed

Bottom line:
-Resistance in ONE capillary > ONE arteriole IN SERIES

-Resistance in arterioles > capillaries (plural) due to PARALLEL arrangement of capillaries

Question 8

Resistance arterioles:

vasodilation

Answer 8

Arterioles:

• Greater blood flow
• Pressure decreased

Capillaries:
-Elevated pressure

Too much

• Risk of edema
• Septic /anaphylactic shock

Question 9

Resistance arterioles:

vasoconstrictions

Answer 9

Arterioles:
-Increase pressure

Capillaries:
-Decreased Pressure

Ex: Pre-eclampisa –> massive vasoconstriction

Question 10

Importance of capacitance & resistance vessels

Answer 10

Arterioles:

• Resistance vessels –> Cause vasoconstriction –> increases afterload (work on heart) = harmful
• Increases peripheral resistance and TPR

Venules/Veins:
Capacitance vessels –> venoconstrict –> Increases venus return –> Increases preload (Helps heart)
-Increases Filling of heart
-Increases EDV

Question 11

What places in the body is blood flow altered and changed based on metabolic demands?

Answer 11

1) Brain
2) Heart
3) Skeletal muscles
- Ex: Exercise

Question 12

Factors that affects resistance

Vasoconstrictors:
Vasodilators:

Answer 12

Vasoconstrictors:
-Sympathetics
-Endothelin
-Serotonin
-Decreasing arteriolar radius
(Increase resistance)

Vasodilators:
-Nitric oxide
-Histamine
-Adenosine
(Decrease resistance)

Question 13

Relationship between cross sectional area, velocity, and flow

Answer 13

small cross sectional area –> blood increased velocity (inverse relationship)

-Capillaries have the
largest cross sectional area and slowest velocity, lowest pressure

Calculations:
1) Velocity = Flow / Cross sectional Area

-Flow = Direct relationship w cross sectional area

Question 14

Calculation for TPR

Answer 14

-Total peripheral resistance = resistance received from organs throughout the body

TPR = MAP - CVP/CO

Question 15

Graves Disease

Answer 15

• Overproduction of Thyroid hormones
• Hyperthyroidism / inc metabolism
• ARTERIOLAR vasodilation = reduced arteriolar resistance =reduced dampening of pulsatile arterial pressure in capillaries