3 - Properties of the Vasculature

Question 1

What type of system is the cardiovascular system?

Answer 1

One way, closed system

Question 2

Layers of Vessels:

Intima

Media

Adventitia

Answer 2

Intima - Innermost, single layer of endothelial cells

Media - Smooth muscle cells, in matrix of collagen, elastin, glycoproteins*

Adventitia - Outermost, collagen, fibroblasts, blood vessels, autonomic nerves (sympathetic adrenergic)

*Ratio of smooth muscle/collagen/elastin determines mechanical characteriistics (e.g. Aorta = more elastin, arterioles = smooth muscles, etc)

Question 3

What is unique about the layers within capillaries?

Answer 3

Only single endothelial layer, Intima

Question 4

How does the Aorta damped pulsatile pressure?

Answer 4

Acts as temporary storage vessel during each heartbeat to accommodate the ejected blood

Question 5

What is the primary vascular regulator of blood pressure?

Answer 5

Arterioles provide primary resistance to flow

Question 6

What vessels have the greatest cross sectional area?

What is unique about these?

Answer 6

Capillaries

Have no smooth muscle

Question 7

Where is most blood volume within the body at any given time?

Answer 7

Venules and veins

Question 8

What allows veins the ability to expand and store blood?

Answer 8

Thin walls provide mechanism to stretch and provide capacitance (blood storage)

Question 9

Where does the largest pressure drop occur within the vascular network?

What causes this drop?

Where does pulsatility disappear?

Answer 9

Through arteriolies

Energy is consumes overcoming resistance

Pulsatility disappears at the level of the capillaries

Question 10

What is the equation for Cross-Sectional Area and Velocities of Blood Flow?

What is the rough trend for velocity?

Answer 10

v = Q / A

v: Velocity of flow (cm/sec)

Q: Flow (mL/sec)

A: Cross-Sectional area (cm²)

Smaller cross sectional area = faster velocity (flow is unchanged)

Question 11

What two factors determine the flow of blood through vessels?

Equation?

Answer 11

1. Pressure Difference (gradient, perfusion pressure)
2. Resistance

F = ΔP / R

F: Flow (or Q)

ΔP: Pressure difference

R: Resistance

Question 12

*How do you determine Resistance (R) ?

What are general trends regarding this?

Answer 12

R = 8nL / πr⁴

Longer = Increase resistance (direct)

Smaller radius = Increase resistance (inverse)

Question 13

Poiseuille’s Equation

General trend to know?

Answer 13

Rate of blood Flow is directly proportional to radius⁴

Question 14

What is the major mechanism for changing blood flow in the CV system?

Answer 14

Changing resistance in blood vessels via radius changes

Question 15

Autonomic Effects:

Sympathetic Stimulation

Answer 15

Stimulation: Constrict vessels, blood flow decrease

Inhibition: Dilates vessels, blood flow increase

Question 16

What is an approximation we make regarding increase to arterial pressure and increase in flow?

Answer 16

Non linear, curved increase due to distanetion of vessels (not rigid tubes)

Question 17

What is the effect of Blood Hematocrit and Blood Viscosity on Vascular Resistance and Blood Flow?

Anemia?

Temperature?

Answer 17

Greater Viscosity = Less Flow

Hematocrit Increases Viscosity

Anemia Decreases Viscosity

Temperature Increases Viscosity

Question 18

Laminare vs Turbulent Flow in Blood Vessels?

Answer 18

Laminar - Orderly, streamlined flow, max velocity at center

Turbulent - Irregular flow, can be caused by obstructions, sharp turns, rough surfaces, high flow

Question 19

Relation of Reynolds Number to Laminar and Turbulent Flow?

(Re > 2000 = Turbulent Flow)

Clinical Representation?

Answer 19

Method to predict when turbulence will occur

Common in Aorta

Small vessels, Re not usually high enough to cause turbulence

Clinical: Turbulent flow is often accompanies by audible vibrations

Murmur = Turbulence in Heart

Bruits = Turbulence in a Vessel

Question 20

How is resistance calculated to vessels within a series?

Total blood flow?

Answer 20

Total resistance = sum of resistance of each vessel

Assume total flow through each blood vessel is the same

Question 21

How do you calculate resistance for blood vessels in parallel?

What type of vessel is this important for?

How is this important for organ arrangement?

Answer 21

Reciprocal of the total resistance is equal to sum of reciprocals of the individual resistances

Parallel Vessels greatly reduce resistance

- - -

Capillaries are arranged in this method; greatly reduces resistance

Parallel arrangment allows independent tissue regulation (vs other areas of body)

Question 22

How do you apply the basic flow equation to series of vessels?

Answer 22

Remember: Q = ΔP / R

Calculate Resistance for Series: 1/R_total=1/R₁ + 1/R₂ + …

ΔP = Pi - Po

You can apply the equation just as a single vessel

Question 23

Vascular Compliance

Answer 23

Compliance = How much volume changes (ΔV) w/change in pressure (ΔP)

C = ΔV / ΔP

Venous System > Arterial System (Compliance)

*The venous system can greatly change its volume with some changes in pressure compared to arteries–i.e. they stretch*

Question 24

Why is some distensibility important for arteries (compliance)?

Answer 24

Reduces pressure of pulsations; greadually decreasing until none at capillaries

Prevents all flow of blood at once during systole, and none during diastole; this ensures constant supply of blood

Question 25

Systolic Pressure Diastolic Pressure Pulse Pressure

Answer 25

Systolic Pressure: Pressure at top of each pulse Diastolic Pressure: Pressure at trough of each pulse Pulse Pressure: Systolic - Diastolic

Question 26

Mean Arterial Pressure (MAP) Equation? What factors **determine** it biologically?

Answer 26

Average of the arterial pressures throughout the cardiac cycle, measured over t ime MAP = P_diastolic + 1/3 (P_systolic - P_diastolic) - - - Cardiac Output (CO): Overall blood flow in total circulation Systemic Vascular Resistance (SVR): Resistance to blood flow offered by all of systemic valculature (**exclude** pulmonary vasculature) Central Venous Pressure: Blood pressure in **throacic vena cava near right atrium** (~ "0") **MAP = (CO x SVR) + CVP**

Question 27

How do we change local blood flow and central arterial pressure? (think in terms of what affects MAP)

Answer 27

Arteriole Radius Whole Body: This changes **Total Peripheral Resistance (TPR),** raising Arterial Blood Pressure at given cardiac output. Constriction = Raise BP Dilation = Lower BP - - - Single Organ/Tissue: Local blood flow altered, w/little effect on TPR or BP (think about **salivary gland** release, doesn't change BP on a large scale)

Question 28

What factors affect Arterial Pulse Pressure (P_p)?

Answer 28

**Stroke Volume (SV)** and **Compliance (C)** P_p = SV / C Application of : ΔP = ΔV / C - - Pp tends to **increase with age** because **reduced** compliance (hardening of the arteries).

Question 29

Clinical: Measuring Systolic and Diastolic Pressures

Answer 29

Direct: Needles or Catheters into peripheral arteries Indirect: Blood pressure cuff (auscultatory) (brachial artery pressure) **Systolic = Beginning of Sounds (turbulent)** **Diastolic = No Sound (laminar)**

Question 30

Venous Pressure and Volume regulation

Answer 30

Due to thin walls, veins are more susceptible to physical influence than arterioles **Increase of tone**, **decrease compliance as walls become stretched**

Question 31

Centra Venous Pressure (CVP) Approximation for what chamber of the heart? What factors influence CVP?

Answer 31

Approximation of **right atrial pressure** **- - -** Clinical: If **Right Ventricle** fails, CVP may be high enough for **jugular impulse to be visible** when patient upright \*Anything causing venous return elevates CVP: 1. Increased blood volume (I.V. injection) 2. Increased large vessel tone (decreased compliance) 3. Dilation of the Arterioles, which decreases peripheral resistance and allows rapid flow of blood from arteries into veins

Question 32

How does gravity affect Venous Pressure? How does blood not just pool below the heart in the lower extremities due to gravity?

Answer 32

Orthostasis (standing) distend veins below heart level; pressure increases in all vessels below heart level, and falls in all above heart level (gravitational impact) - - - Veins have one-way valves that permit blood flow **toward heart**

Question 33

What is the Skeletal Muscle Pump?

Answer 33

Method veins use to facilitate blood flow back to the heart. Veins surrounded by skeletal muscle are squeezed, pushing blood back to heart (valves prevent back flow)

Question 34

Clinical: Varicose Veins

Answer 34

Venous valves become incompetent, muscle pumping becomes ineffective. Blood volume and pressure increase in the veins of dependent limbs--increase capillary pressure, may cause **edema**

Question 35

What is the Respiratory Pump?

Answer 35

Inspiration facilitates venous return, leads to **increase in atrial and ventricular preloads** Expiration, **venous return falls** - - - We can force expiration: Valsalva, Coughing Net effect: Increase Venous Return / Cardiac Output