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Physiology > Circulation (B 2: W 2) > Flashcards

Circulation (B 2: W 2) Flashcards

1
Q

What is hemodymamics?

A

Field concerned with the relationship among the physical principles governing pressure, flow, resistance, and compliance as they relate to the cardiovascular system

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2
Q

What are the functions of peripheral circulation?

A
  • Carry blood
  • Exchange: nutrients, waste products, gases
  • Transport: hormones, enzymes, nutrients, components of immune system, gases, waste products
  • Regulate blood pressure
  • Direct blood flow
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3
Q

What does it mean that circulation is a closed circuit?

A

Modification of blood flow in one part of the system affects blood flow in other parts

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4
Q

What is the significance of the branching pattern of the ciruclatory system?

A

Branches from large to small

Important for blood pressure

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5
Q

What is the significance of the serial paths of the systemic and pulmonary circuits in circulation?

A

There is an equal amount of blood going to pulmonary circulation as there is going to peripheal circulation

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6
Q

What is an example of capillary beds in series?

A

The kidneys

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7
Q

What are some characteristics of arteries?

A
  • Deliver oxygenated blood to the tissue
  • Transport blood under high pressure
  • Have strong vasuclar wall
  • Have rapid pulsatile blood flow
  • Are densely innervated
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8
Q

What is the purpose for the strong muscular wall and pulsatile flow of arteries?

A

Strong wall due to high pressure

Pulsatile flow due to exposure to different pressures during systole and diastole

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9
Q

What are characteristics of artierioles?

A
  • Smalles branches of arteries (5-100 micron diameter)
  • Major resistance vessels of the whole peripheral circulation - also outnumber any other type of artery
  • Have thick smooth muscle layer - more muscular in proprtion to diameter
  • Are densely innervated
  • Regulate blood flow to capillary beds
  • Biggest pressure drop (stopcocks of the circulation)
  • Partially contracted under normal conditions (basal tone)
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10
Q

Which blood vessel determines resistance of the entire circulatory system?

A

Arterioles - the stopcocks

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11
Q

What is the purpose of having resting basal tone in the vasculature?

A
  • In order to vasoconstrict, you need a vessel that is not fully constricted to start with
  • In order to vasodilate, you need a vessel that is not fully relaxed
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12
Q

What is the difference between skeletal muscle and vascular smooth muscle in regards to basal tone?

A

Vasculature has some tone without needing neural input

The basal tone probably comes from intrinsic and local factors

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13
Q

How do voltage-gated L-type Ca channels influence basal tone

A
  • At -60 mV there is no calcium influx
  • Arterioles rest at about -50 mV
    • Some Ca influx
    • Maintain basal tone
  • Veins are much more hyperpolarized
    • -70 mV
    • That’s why they don’t have basal tone
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14
Q

What are the characteristics of capillaries?

A
  • Very small (5-10 microns)
  • No smooth muscle
  • Thin walls of a single layer of endothelium - permeable to small molecule substances
  • Major exchange vessels
  • Have the largest total cross-sectional area
  • Have low flow velocity
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15
Q

What are the characteristics of venules?

A
  • Small vessels (20 microns) with thin walls
  • Collect blood from the capillaries
  • Also participate in exchange
  • Gradually coalesce into progressively larger veins
  • **The total cross-sectional area diminishes, and the velocity of blood flow increases **
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16
Q

What are the characteristics of veins?

A
  • Progressively merge to form larger veins
  • Transport blood from tissues back to the heart
  • Major capcitance vessels = major collection and storage site for blood (major controllable reservoir)
  • Thin but muscular walls
  • Are under low pressure
  • Are densely innervated
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17
Q

What percentage of the blood volume of the body is in systemic versus pulmonary circulation?

A
  • 85% of blood volume in systemic circulation
    • 65% in the veins
  • 15% in heart and lungs
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18
Q

How does cross-sectional area relate to velocity of blood flow between the vessels?

A
  • Arteries have lowest cross-sectional area with highest velocity
  • Veins have a slightly higher cross-sectional area, with lower velocity
  • Capillaries have a very large cross-sectional area and the blood velocity is very low there (related to capillary function)
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19
Q

Which great vessel has a lower cross-sectional area?

A

Aorta

2.5 cm2 as compared to 8 cm2 in the vena cava

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20
Q

How do we calculate the velocity of blood flow?

A

v = Q/A

Q = blood flow

A = cross-sectional area

Velocity is directly proportional to blood flow and inversely proportional to the cross-sectional area

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21
Q

Why does blood velocity decrease from aorta to capillaries?

A
  • Greater distance, more friction to reduce speed
  • Smaller radii of arterioles and capillareis offers more resistance
  • Farther from heart, the number of vessels and their total cross-sectional area become greater and greater
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22
Q

How does the low velocity of blood flow in capillaries optimize their function?

A

Optimizes conditions for exchange of substances in the capillary wall

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23
Q

Why does arterial pressure fluctuate between systolic (120 mmHg) and diastolic (80 mmHg) pressure levels?

A

Because pumping by the heart is pulsatile

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24
Q

What is the definition of blood pressure?

A

The force exerted by the blood against any unit area of the vessel wall

25
Q

Where does the largest decrease in pressure occur across the circulatory system?

A

In the arterioles, because they are the site of highest resistance

26
Q

Since arterial pressure is pulsatile, how is it possible that capillary pressue is essentially non-pulsatile?

A

Pulse pressure is dampened over the course of the arterial tree due to:

  • Compliance of the arterial vessel walls
  • Resistance to flow as vessel diameter becomes smaller
27
Q

In what disease is the dampening of pulsatile arterial pressure diminished, and pulsatile flow in the capillaries can be observed in the finger nail beds?

A

Graves’ Disease (hyperthyroidism)

  • Areriolar vasodilation
  • Reduced arteriolar resistance
  • Pulsatile flow in capillaries affects the exchange
28
Q

What is the most important determinant of pulse pressure?

A

Stroke volume

The pulse pressure increases to the same extent as the systolic pressure

29
Q

Which patients are likely to have very small arterial pulse pressures and why?

A

Patients with congestive heart failure or who have had a severe hemorrhage

Because their stroke volumes are abnormally small

30
Q

Which patiens are likely to have increased arterial pulse pressure and why?

A

Patients with aortic reguritations

Because they have large stroke volumes

31
Q

Mean arterial pressure (MAP) is the average arterial pressue with respect to time. How is it calculated?

A

MAP = 1/3 systolic pressure + 2/3 diasotlic presure

32
Q

How is atrial pressure measured?

A

L atrial pressure is estimated by the pulmonary wedge pressure

A catheter is inserted into the smallest branches of the pulmonary artery - makes almost direct contact with the pulmonary capillaries

THe measured capillary pressure is approx. equal to the L atrial pressure

33
Q

Pressure gradient drives blood flow. How is it calculated?

A

Ohm’s Law

Q = dP/R

Q = blood flow

dP = pressure gradient

R = resistance

The blood flow is inversely propotional to the resistance

34
Q

These two blood vessels have very different blood pressures. Which one has more blood flow?

A

They have the same amount of blood flow

*The pressure difference, not the absolute pressure, determines flow

35
Q

What is compliance (or capacitance)?

A

The total quantity of blood that can be stored in a given portion of the circulation for each mmHg pressure rise

Describes the distensibility of blood vessels

Vessels are elastic and expand when blood is in them under pressure

36
Q

How do you calculate capacitance?

A

C = dV/dP

C = capacitance

V = volume

P = pressue

37
Q

Which has greater capacitance, arteries or veins?

A

Veins

38
Q

What determines the capacitance of a vessel?

A

The relative proportion of elastin fibers versus smooth muscle and collagen in the vessel wall

39
Q

What effect does aging have on vascular compliance?

A

As aging occurs, the arteries become stiffer and less distensible - decreased compliance

Thus, a given increse in volume causes a larger increase in pressue

40
Q

What causes atherosclerosis, or “hardening of the artery”?

A

Caused by the formation of multiple plaques within the arteries

Results from a deposition of tough, rigid collagen inside the vessel wall and around the atheroma

41
Q

What factors affect the resistance of a blood vessel?

A
  • Blood viscosity
  • Blood vessel length
  • Radius of the vessel

The only one that can be easily altered to affect resistance is the radius

42
Q

How do we calculate resistance?

A

Poiseuille’s Law

R = 8nl/πr4

n = blood viscosity

l = length

r = radius

43
Q

In what two ways does increased arterial pressure increase the blood flow?

A
  1. Increased force
  2. Vascular wall distention (decreased vascular resistance)
44
Q

How does sympathetic activity affect blood flow?

A
  • Inhibiton of sympathetic activity dilates the vessels
    • Can increase blood flow twofold or more
  • Sympathetic stimulation can constrict blood vessels so much that blood flow occasionally decreases to zero for a few seconds, despite high arterial pressure
45
Q

How is parallel resistance calculated?

A

1/Rtotal = 1/Ra + 1/Rb + … 1/Rn

  • The total resistance is less than the resistance of any of the individual arteries
  • Each artery in parallel receives a fraction of the total blood flow
  • In each parallel artery, the pressure is the same
46
Q

How is series resistance calculated? (arragements of blood vessels within a given organ)

A

Rtotal = Rarteries + Rarterioles + Rcapillaries

  • The largest proportion of resistance in this series is contributed by the arterioles
  • Each blood vessel in a series receives the same total blood flow
  • As blood flows through the series, the pressure decreases
47
Q

What is the total peripheal resistance (TPR)?

A

The complete resistance that blood encounters as it flows from the arterial to the venous side of circulation

48
Q

What element of resistance is affected by the hematocrit?

A

Related to viscosity

Hematocrit = the percentage of blood that is RBCs

49
Q

In what condition is the viscosity of blood increased more than twofold?

A

Polycytemia vera - increased number of RBCs

Sluggish blood

50
Q
A
51
Q

At low hematocrit, why is blood viscosity still higher than that of plasma?

A

Due to stickiness of red blood cells

52
Q

Why does viscosity increase at higher hematocrits?

A

Due to cell deformation

53
Q

What are the characteristics of laminar flow?

A
  • Streamlined
  • Flows in layers
  • Faster in center
  • Flow is only proportional to driving force in laminar flow
54
Q

How does axial steaming affect blood flow?

A
  • As flow rate increases, blood cells move toward center (axial streaming) where velocity is the highest
  • Lowers the apparent viscosity of the blood
55
Q

What is the difference between laminar flow and turbulent flow?

A
  • Turbulent flow - blood flows in all directions, fastest velocities are not necessarily in the middle of the stream
  • Energy is lost in turbulence, so flow does not increase as much for a given rise in pressure as the critical velocity is exceeded
  • Turbulent flow is not good
    • Waste removal is not sufficient
    • Tissues do not get enough oxygen
56
Q

How is critical velocity calculated?

A

Reynold’s Number

Ng = Vdp/n

V = mean velocity

d = diameter

p = fluid density

n = fluid viscosity

57
Q

How is Reynold’s number (and therefore turbulence) increased?

A
  • Decreased blood viscosity (e.g. reduced hematocrit, anemia)
  • Increased blood velocity (e.g. narrowing of blood vessel followed by a precipitous increase in internal diameter)
58
Q

How does change in radius from very narrow to very wide affect blood flow?

A

Creates higher velocity goig through

Turbulence can result

Physiology (29 decks)

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