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Unit 4 Physiology > Microcirculation > Flashcards

Microcirculation Flashcards

1
Q

how is blood viscosity anomalous? is it newtonian under physiological conditions?

A

it is not constant under all conditions

yes

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2
Q

what graph is viscosity the slope of?

A

shear stress vs shear rate plot

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3
Q

under what conditions is blood not a newtonian fluid?

A

at lower flow rates

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4
Q

what is a yield shear stress?

A

at lower flow rates, blood requires a threshold force to get moving

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5
Q

what is polycythemia?

A

abnormally elevated hematocrit

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6
Q

what are the five determinants of blood viscosity?

A

fibrinogen, hematocrit, vessel radius, velocity and temperature

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7
Q

what is the relationship between the flow and pressure of a newtonian fluid?

A

linear

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8
Q

why do low flow rates of blood appear to have more resistance?

A

formation of rouleaux at low velocities that break up as blood flow increases

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9
Q

what happens to the viscosity of blood when hematocrit increases from 40-60%?

A

it doubles

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10
Q

what is a phlebotomy?

A

removal of excess red blood cells

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11
Q

what is the fahraeus-lindqvist effect?

A

that the apparent viscosity of blood depends on the diameter of the tube through which it is flowing

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12
Q

what happens to blood in tubes with a diameter less than 0.3 mm?

A

the apparent viscosity of the blood decreases

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13
Q

what is axial streaming?

A

the tendency for red blood cells to flow in the fast moving laminar flow part of the stream

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14
Q

what is the result of axial streaming?

A

RBC move through small vessels faster than plasma resulting in lower hematocrit in those vessels and therefore lower viscosity

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15
Q

what are rouleaux?

A

chain like aggregates of RBC which form at low flow rates

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16
Q

what is plasma skimming?

A

tendency of plasma to be skimmed off into a branch of the circulation because it flows near the edges of the flow due to axial streaming of red blood cells

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17
Q

what prevents plasma skimming?

A

arterial cushions near the branch points that cause turbulence before the blood moves into the branch

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18
Q

what is cellular deformability?

A

the ability for RBC to bend in order to squeeze through small capillaries

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19
Q

what occurs if RBC are unable to deform when moving though small capillaries?

A

it may lead to blockage of flow and ischemia

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20
Q

what are the three functions of microcirculation?

A

nutritional source
filtration in renal glomeruli
thermoregulation in the skin

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21
Q

what do capillaries connect?

A

arterioles and venules

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22
Q

what is one possible function of a metarteriole?

A

to shunt blood to bypass a capillary network

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23
Q

what controls local flow within the capillary network?

A

precapillary sphincters

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24
Q

how are precapillary sphincters signaled to contract or release? what, in general, results in their opening?

A

they respond to local conditions to oxygen, CO2 and acidity mainly
hypoxia leads to opening

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25
Q

how does the flow react in microcirculation to varying pressure? why?

A

subtle changes affect flow velocity and direction because the pressure differences at the beginning and end are not very substantial

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26
Q

what is a metarteriole?

A

a blood vessel that connects from the arteriole to the venule and has inward blood flow from some capillaries. may shunt blood if the capillary bed is bypassed

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27
Q

what is the structure of a capillary?

A

a single layer of endothelial cells surrounded by a basement membrane

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28
Q

what is the diameter range of a capillary? of a RBC?

A

4-10 microns

8 microns

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29
Q

how do capillaries vary?

A

in their degree of leakiness

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30
Q

which are the most common capillary subtype? what is a defining feature?

A

continuous capillary

contain interendothelial junctions

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31
Q

what is different about continuous capillaries in the brain?

A

there are no interendothelial junctions but tight junctions instead

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32
Q

what are fenestrated capillaries and where are they located?

A

their endothelial cells have conduits that permit flow of fluid and ions across the endothelium
located in exocrine glands or epithelial membranes (small intestine)

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33
Q

what are discontinuous capillaries? where are they found?

A

have fenestrations and large gaps between endothelial cells

found in liver sinusoids

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34
Q

where is capillary density low?

A

low O2 consumption tissues like the joints and cartilage

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35
Q

what percentage of muscle capillaries are perfused at erst? how does this increase?

A

20%

increases with precapillary sphincter relaxation

36
Q

what is convective transport?

A

transport of substances between organs within the cardiovascular system

37
Q

what does the transport rate of a substance in the blood depend on?

A

flow rate and concentration

38
Q

what is the fick principle?

A

transcapillary efflux rate= flowx concentration in arteries-concentration in veins

39
Q

what causes the transcapillary efflux rate to be negitive?

A

the tissue is producing a substance

40
Q

what is the farthest distance between a cell and a capillary?

A

10 micrometers

41
Q

what four factors determine the diffusion rate of a substance from ECF to capillaries?

A

concentration difference, surface area for exchange, diffusion distance and permeability of the capillary to that substance

42
Q

what does fick’s first law of diffusion sate?

A

the flux is directly proportional to the area of the membrane and to the concentration across the membrane

43
Q

what is flux?

A

the number of moles that diffuse across the membrane during an interval of time

44
Q

what is the diffusion coefficient?

A

the flux when the area and concentration gradient are in unity

45
Q

when is flux negative and when is it positive?

A

it is positive with an efflux from the plasma and negative with an influx to the plasma

46
Q

what increases the diffusion coefficient?

A

increased temperature and with small solutes

47
Q

what does area represent in fick’s law of diffusion?

A

the area of the membrane available for diffusion

48
Q

what does the presence of solute on one side of a membrane do the chemical potential of water?

A

decreases it

49
Q

what does hydrostatic pressure in a tube do to the chemical potential of the water in a solutino?

A

it increases it

50
Q

what is osmotic pressure?

A

the hydrostatic pressure that would stop the flow of water into a solution

51
Q

what are the six things that net shifts between capillary and interstitial compartments are important for?

A

maintenence of blood volume, interstitial fluid absorption, edema formation, saliva, sweat and urine production

52
Q

what four pressures are involved in capillary fluid balance?

A

capillary and interstitial fluid hydrostatic pressure (P) and capillary and interstitial fluid osmotic pressure (pi)

53
Q

what is the starling equation?

A

capillary flow=L(hydraulic conductivity) x pressure summation

54
Q

how does one summate pressure in the for the starling equation?

A

[(Pc-Pif)-(Pi c-Pi if)]

55
Q

how does fluid travel out of the capillaries?

A

trancellularly and paracellularly

56
Q

how does fluid travel through the capillary endothelium transcellularly? paracellularly?

A

trans- aquaporin channels in capillary endothelial membranes

para-through interendothelial clefts, fenestrae or gaps

57
Q

how do gasses and other small solutes cross the capillary membrane? water?

A

gas-diffusion

water-convection

58
Q

how is flow into and out of the capillaries quantified?

A

flow from capillaries to IF is positive, flow to the capillaries from the IF is negative

59
Q

what does a positive hydrostatic pressure difference cause? a positive osmotic pressure difference?

A

hydrostatic-positive flow of water

osmotic-negative flow of water

60
Q

what is hydraulid conductivity?

A

constant of proportionality that relates amount of flow to the driving force

61
Q

how does capillary hydrostatic pressure change along the length of the capillary?

A

it falls linearly starting at 35 mmHg and ending at 15 mmHg

62
Q

what is the Pc in the middle of a capillary?

A

the averages of the Pc at the venuolar and arteriolar end

63
Q

besides along the length of a capillary,where does Pc vary?

A

in different tissues (higher in kidneys for filtration)

64
Q

like other blood pressures, what other force affects Pc?

A

gravity

65
Q

what changes in vessel diameter increase capillary hydrostatic pressure?

A

arteriolar dilation or venular constriction

66
Q

what changes in vessel diameter decrease capillary hydrostatic pressure?

A

arteriolar constriction or venular dilation

67
Q

what contributes to the total osmotic pressure of plasma? which is primary?

A

salts and proteins (primary)

68
Q

what does the gibbs donnan equilibrium do? what is its cause?

A

increases the excess salt in the plasma

exerted by the plasma proteins that are charged and sequester other charged molecules around them (electroneutrality)

69
Q

what is the total protein concentration in the blood and what does albumin contribute to that?

A

total-7 g/dl or 1.5 mM

albumin-5 g/dl or 1 mm

70
Q

what are the three major plasma proteins?

A

albumin, globulins and fibrinogen

71
Q

what is the colloid osmotic pressure of the plasma? what are the contributions?

A

25 mmHg

plasma proteins and excess salt

72
Q

what is needed to correct van’t hoff’s law for actual measured osmotic pressure?

A

a coefficient specific for the specific solute

73
Q

what is the sign of the hydrostatic pressure in loose tissue and encapsulated organs?

A

negative in loose tissue and positive in encapsulated organs

74
Q

what can occur with the addition of fluids to the interstitial compartment? when is this a concern?

A

disruption of the solid phase collagen fibers and proteoglycan gel
edema

75
Q

what direction does an increase in interstitial fluid hydrostatic pressure drive fluid?

A

negatively-absorption into capillaries

76
Q

what is the body average interstitial fluid osmotic pressure? what does this drive?

A

3 mmHg

drives fluid into tissue and out of capillaries

77
Q

what occurs at the arteriolar end of the capillary? the venule end?

A

arteriole- filtration out of capillary

venule- capillary absorption

78
Q

what causes the change from filtration to absorption along the capillary?

A

decrease in capillary hydrostatic pressure and increase in IF osmotic pressure ( P if and Pi c remain the same)

79
Q

what causes the net increase in IF osmotic pressure along the length of a capillary bed?

A

fluid leaving the capillary contains plasma protein

80
Q

in the entire capillary bed, what is the net movement of fluid? what is the value?

A

there is a net filtration into the IF (neglecting glomerular filtration)
2-4 L/day

81
Q

how are capillaries different than initial lymphatics?

A

there are one way valves in lymph vessels

82
Q

what does lymph accommodate? how much fluid does it collect per day?

A

it accommodates for the net filtration into the IF by the capillaries
2-4 L/day

83
Q

what types of diseases cauase edema?

A

relan, cardiac lung and hepatic diseases

84
Q

what is ascites?

A

fluid from hepatic and intestinal capillaries moving from the interstitium into the peritoneal cavity

85
Q

why can liver disease cause edema?

A

because the liver synthesizes albumin- the major factor in capillary osmotic pressure

Unit 4 Physiology (31 decks)

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