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Unit 5 > 11/25/2014 Medical Physiology Microcirculation Barry Knox > Flashcards

11/25/2014 Medical Physiology Microcirculation Barry Knox Flashcards

1
Q

What are the five main influencers of blood viscosity?

A
  1. Fibrinogen
  2. Hematocrit
  3. Vessel radius
  4. Velocity
  5. Temperature
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2
Q

What are roleaux?

A

Stacks of RBC’s that kind of clump together in a line, at low flow rates of blood

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3
Q

_____ is the volume fraction of blood occupied by RBCs

A

Hematocrit

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4
Q

When hematocrit increases from 40-60%, as in _____, blood viscosity doubles.

A

Polycythemia

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5
Q

What is polycythemia?

A

Abnormal increase in RBC proportion and/or elevated hematocrit

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6
Q

What is one common effect of polycythemia?

A

Hypertension, because with the increase in viscosity comes an increase in resistance to flow, and the heart has to pump harder to get the blood moving.

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7
Q

What is the treatment for polycythemia?

A

Remove excess RBCs via phlebotomy (needle stick) to restore normal hematocrit.

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8
Q

What is the Fahraeus-Lindqvist effect?

A

The apparent viscosity of blood also depends on the diameter of the vessel in which its traveling. At diameters less than 0.3mm, blood viscosity decreases.

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9
Q

T/F: Even though the viscosity of blood decreases in smaller tube diameters, the viscosity of plasma and saline remains the same regardless of the vessel in which it’s traveling.

A

True

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10
Q

The low viscosity of blood in tubes of small diameter has been explained by “axial streaming.” What is this?

A

Axial streaming is the tendency of RBCs to accumulate in rapidly flowing axial lamina. If RBC’s end up in the fast part of the stream, they move through quickly and don’t clump, thereby reducing the hematocrit of that portion of the stream and decreasing the viscosity.

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11
Q

What are the four nondieal rheological effects?

A
  1. Formation of Roleaux
  2. Axial streaming aka plasma skimming
  3. Cellular deformability
  4. Fahraeus-Lindqvist effect
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12
Q

What does rheological mean?

A

The study of what happens to a material (blood) under pressure, or strain, in other words, how it deforms.

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13
Q

The turnover for all RBCs is every 120 days. How many turn over in one day?

A

1%, or about 250 billion per day are released from the marrow.

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14
Q

What is one reason for altered hematocrit, besides axial streaming?

A

Plasma skimming. The plasma collects on the outer edges of the vessel and at a fork, follows the bifurcation, leaving the majority of RBCs in the main vessel, leading to a higher than actual hematocrit level.

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15
Q

Cellular deformability is a property of RBCs that allows them to get through narrow spaces. What is one condition where this property is lost?

A

Sickle cell anemia, leading to irreversible sickled cells, can cause ischemia, severe pain and organ damage from non-perfusion.

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16
Q

In laminar flow, why do leukocytes move much more slowly than RBCs?

A

Because they have adhesive properties which allow them to stick to endothelium, in case they care called to the scene of an infection (immune surveillance).

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17
Q

What constitutes a microcirculatory circuit?

A

From an arteriole to a venule.

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18
Q

T/F: Venules are surrounded by smooth muscle.

A

True-ISH. The vascular smooth muscle that surrounds smooth muscle is discontinuous, whereas the vascular smooth muscle around arterioles is a continuous single layer.

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19
Q

Are metarterioles present in all microcirculatory circuits? What function do they serve?

A

No, metarterioles are present in only some circuits, and serve to bypass the capillary bed.

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20
Q

What structure in the microcirculatory circuit controls the local flow within the capillary network, and despite having no nervous innervation, is effective as responding to local conditions of oxygen (ie dilating in response to hypoxia), CO2, and acidity?

A

Precapillary sphincters

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21
Q

The function of the microcirculatory unit depends on the tissue:
__1__ in vascular beds, __2__ in renal glomeruli, __3__ in skin

A
  1. nutrient providing and waste removal
  2. filtration
  3. thermoregulation
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22
Q

Where are precapillary sphincters often found?

A

Along metarterioles, where vessels branch off and become capillaries.

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23
Q

What is a capillary?

A

A single layer of endothelial cells surrounded by a basement membrane; the diameters range from 4-10 microns. (RBC diameter is 8 microns)

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24
Q

What are the three types of capillaries?

A
  1. Continuous
  2. Fenestrated
  3. Sinusoidal or discontinuous
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25
Q

_____ are the most common capillary, with interendothelial junctions that are 10-15 nm wide.

A

Continuous capillaries.

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26
Q

What is the special difference between continuous capillaries in the brain vs in the rest of the body?

A

The junctions are tight, thus giving rise to the blood brain barrier.

27
Q

Where are fenestrated (windows) capillaries often found?

A

They often surround exocrine glands and epithelial membranes ie the small intestine. This endothelium has fenestrations that allow the filtration of solutes and fluid.

28
Q

Where are discontinuous capillaries found? These capillaries have large gaps between their endothelial cells.

A

Liver sinusoids

29
Q

Where is capillary density the highest?

A

In organs or tissues that require lots of O2 consumption, ie the heart.

30
Q

Substances are carried between organs within the cardiovascular system by _______, meaning that substances are carried along with the flow of blood.

A

Convective transport

31
Q

Convective transport depends on the concentration of the substance and the flow rate. What is the corresponding equation?

A

Transport rate of A = Flow rate x [A]
For example:
Flow of O2 in arteries (mL O2/min) = CO (L blood/min) x arterial O2 content (mL O2/min)

32
Q

Explain the Fick principle:

Transcapillary efflux rate (mass/time) = Q x [A arterial - A venous]

A

Tissue rate of utilization of substance A OR production of substance A by the tissue is measured from the going-in amount (A arteriole concentration) and the going-out amount (A venous concentration).

33
Q

What does is mean if the transcapillary efflux rate of a substance is negative?

A

[A arterial - A venous]
If negative, the venous side has more of A,
the organ or tissue must therefore be making A

34
Q

No cell is more than 10 microns from what?

A

A capillary. This allows for diffusion

35
Q
  1. Concentration difference of a substance in the vessel vs in the outside area
  2. Surface are available for exchange
  3. Diffusion distance
  4. Permeability of the capillary wall
    These four properties determine what?
A

How diffusion happens, the rate of diffusion of a substance between blood and interstitium.

36
Q

What equation is this?

J = DA ( [cp - ci] / l )

A

Fick’s law of diffusion:
J = flux (moles/s)
D = diffusion coefficient, a characteristic of the solute and membrane (cm/s)
l = thickness of the membrane (m)
cp, ci = concentration in plasma and interstitium, respectively (moles/cm^3)

37
Q

Normal plasma has a total osmotic pressure of ___?

A

About 5000 mm Hg

38
Q

What is osmosis?

A

The Movement of water from an area with less concentration of solute to an area of more concentration of solute, across a semipermeable membrane.

39
Q

Osmotic pressure is the hydrostatic pressure needed to balance what?

A

The movement of the solute

40
Q

Filtration in transcapillary fluid movement means which direction?

A

Out of the vessel

41
Q

Absorption in transcapillary fluid movement means which direction?

A

In to the vessel

42
Q

Where is the only place in the body that undergoes rapid filtration that is normal?

A

Kidneys. Rapid filtration anywhere else leads to edema.

43
Q

Give the Starling equation.

A

Jv = Lp x [ ( Pc - Pif ) - ( OSMc - OSMif ) ]
where OSM is symbol for pie
P = hydrodtatic pressure
OSM = osmotic pressure
This equation determines whether a substance is being absorbed of filtered.

44
Q

In the Starling equation, a + hydrostatic pressure means what?

A

Positive flow of water from capillaries to interstitium.

45
Q

In the Starling equation, a + osmotic pressure means what?

A

Flow of water from the interstitium to the capillaries.

46
Q

T/F: Pc (hydrostatic pressure of the capillaries) is influenced by gravity.

A

True

47
Q

Along the length of a capillary, where is Pc (hydrostatic pressure of the capillary) lowest?

A

At the venous end of the capillary, meaning that less filtration occurs at the venous end of the capillary.

48
Q

Arteriolar dilation or venular constriction tend to ____ capillary hydrostatic pressure.

A

Increase

49
Q

Arteriolar constriction or venular dilation tend to _____ capillary hydrostatic pressure.

A

Decrease

50
Q

Total osmotic pressure of plasma is due to what substances?

A

Proteins, ie fibrinogen, albumin, globulins, and salts

51
Q

Capillary colloid osmotic pressure is a force that always favors which direction of movement?

A

Fluid absorption

52
Q

Colloid osmotic pressure of plasma is about how much?

A

25 mm HG, the combined effects of proteins and salt excess in the capillaries vs the interstitium.

53
Q

T/F: Albumin is found both in blood plasma and the interstitium.

A

FALSE. Albumin is only found in blood plasma, which helps to contribute to the Gibbs-Donnan equilibrium os plasma and interstitial fluid.

54
Q

Where can you find a Pif (Hydrostatic pressure of insterstitial fluid) that is negative? That is positive?

A
  • Pif in soft or loose tissue ie. lung, subcutaneous tissue (drives fluid filtration), ie. -2 mm HG
    + Pif in encapsulated/rigid organs such as bone marrow, brain and kidney (drives fluid absorption), ie. 1-3 mm HG
55
Q

What substance types (phases) exist in the interstitium?

A

Generally fluid and solid gel (collagen, proteoglycans) phases

56
Q

Why is filtration more likely in the arteriolar end of a capillary, and absorption more likely at the venous end of a capillary?

A

Fluid leaving the capillary at the proximal/arteriolar end contains plasma protein, resulting in a gradual increase of interstitial colloidal osmotic pressure along the length of the capillary bed. The decreased capillary hydrostatic pressure dominates, causing more filtration at the venous end of the capillary.

57
Q

T/F: There is a net daily filtration out of the capillaries.

A

True, it is about 2-4 L/day.

58
Q

What is edema?

A

Excess water and salt in the interstitial space

59
Q

Left heart failure leads to what kind of edema?

A

Pulmonary edema (also can be caused by pulmonary HTN)

60
Q

Right heart failure leads to what kind of edema?

A

Edema in the lower extremities.

61
Q

What is ascites?

A

Edema caused by liver dysfunction

62
Q

What happens in liver failure w/r/t albumin?

A

The liver stops making albumin, and with low or no albumin in the blood, peripheral edema occurs

63
Q

SIADH (inappropriate secretion of ADH) causes what?

A

Peripheral edema

64
Q

What is one cause of lymphatic blockage that might result in edema?

A

Malignant neoplasm

Unit 5 (36 decks)

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