Microcirculation

Question 1

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

Answer 1

it is not constant under all conditions

yes

Question 2

what graph is viscosity the slope of?

Answer 2

shear stress vs shear rate plot

Question 3

under what conditions is blood not a newtonian fluid?

Answer 3

at lower flow rates

Question 4

what is a yield shear stress?

Answer 4

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

Question 5

what is polycythemia?

Answer 5

abnormally elevated hematocrit

Question 6

what are the five determinants of blood viscosity?

Answer 6

fibrinogen, hematocrit, vessel radius, velocity and temperature

Question 7

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

Answer 7

linear

Question 8

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

Answer 8

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

Question 9

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

Answer 9

it doubles

Question 10

what is a phlebotomy?

Answer 10

removal of excess red blood cells

Question 11

what is the fahraeus-lindqvist effect?

Answer 11

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

Question 12

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

Answer 12

the apparent viscosity of the blood decreases

Question 13

what is axial streaming?

Answer 13

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

Question 14

what is the result of axial streaming?

Answer 14

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

Question 15

what are rouleaux?

Answer 15

chain like aggregates of RBC which form at low flow rates

Question 16

what is plasma skimming?

Answer 16

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

Question 17

what prevents plasma skimming?

Answer 17

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

Question 18

what is cellular deformability?

Answer 18

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

Question 19

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

Answer 19

it may lead to blockage of flow and ischemia

Question 20

what are the three functions of microcirculation?

Answer 20

nutritional source
filtration in renal glomeruli
thermoregulation in the skin

Question 21

what do capillaries connect?

Answer 21

arterioles and venules

Question 22

what is one possible function of a metarteriole?

Answer 22

to shunt blood to bypass a capillary network

Question 23

what controls local flow within the capillary network?

Answer 23

precapillary sphincters

Question 24

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

Answer 24

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

Question 25

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

Answer 25

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

Question 26

what is a metarteriole?

Answer 26

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

Question 27

what is the structure of a capillary?

Answer 27

a single layer of endothelial cells surrounded by a basement membrane

Question 28

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

Answer 28

4-10 microns | 8 microns

Question 29

how do capillaries vary?

Answer 29

in their degree of leakiness

Question 30

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

Answer 30

continuous capillary | contain interendothelial junctions

Question 31

what is different about continuous capillaries in the brain?

Answer 31

there are no interendothelial junctions but tight junctions instead

Question 32

what are fenestrated capillaries and where are they located?

Answer 32

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

Question 33

what are discontinuous capillaries? where are they found?

Answer 33

have fenestrations and large gaps between endothelial cells | found in liver sinusoids

Question 34

where is capillary density low?

Answer 34

low O2 consumption tissues like the joints and cartilage

Question 35

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

Answer 35

20% | increases with precapillary sphincter relaxation

Question 36

what is convective transport?

Answer 36

transport of substances between organs within the cardiovascular system

Question 37

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

Answer 37

flow rate and concentration

Question 38

what is the fick principle?

Answer 38

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

Question 39

what causes the transcapillary efflux rate to be negitive?

Answer 39

the tissue is producing a substance

Question 40

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

Answer 40

10 micrometers

Question 41

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

Answer 41

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

Question 42

what does fick's first law of diffusion sate?

Answer 42

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

Question 43

what is flux?

Answer 43

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

Question 44

what is the diffusion coefficient?

Answer 44

the flux when the area and concentration gradient are in unity

Question 45

when is flux negative and when is it positive?

Answer 45

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

Question 46

what increases the diffusion coefficient?

Answer 46

increased temperature and with small solutes

Question 47

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

Answer 47

the area of the membrane available for diffusion

Question 48

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

Answer 48

decreases it

Question 49

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

Answer 49

it increases it

Question 50

what is osmotic pressure?

Answer 50

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

Question 51

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

Answer 51

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

Question 52

what four pressures are involved in capillary fluid balance?

Answer 52

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

Question 53

what is the starling equation?

Answer 53

capillary flow=L(hydraulic conductivity) x pressure summation

Question 54

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

Answer 54

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

Question 55

how does fluid travel out of the capillaries?

Answer 55

trancellularly and paracellularly

Question 56

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

Answer 56

trans- aquaporin channels in capillary endothelial membranes | para-through interendothelial clefts, fenestrae or gaps

Question 57

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

Answer 57

gas-diffusion | water-convection

Question 58

how is flow into and out of the capillaries quantified?

Answer 58

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

Question 59

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

Answer 59

hydrostatic-positive flow of water | osmotic-negative flow of water

Question 60

what is hydraulid conductivity?

Answer 60

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

Question 61

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

Answer 61

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

Question 62

what is the Pc in the middle of a capillary?

Answer 62

the averages of the Pc at the venuolar and arteriolar end

Question 63

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

Answer 63

in different tissues (higher in kidneys for filtration)

Question 64

like other blood pressures, what other force affects Pc?

Answer 64

gravity

Question 65

what changes in vessel diameter increase capillary hydrostatic pressure?

Answer 65

arteriolar dilation or venular constriction

Question 66

what changes in vessel diameter decrease capillary hydrostatic pressure?

Answer 66

arteriolar constriction or venular dilation

Question 67

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

Answer 67

salts and proteins (primary)

Question 68

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

Answer 68

increases the excess salt in the plasma | exerted by the plasma proteins that are charged and sequester other charged molecules around them (electroneutrality)

Question 69

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

Answer 69

total-7 g/dl or 1.5 mM | albumin-5 g/dl or 1 mm

Question 70

what are the three major plasma proteins?

Answer 70

albumin, globulins and fibrinogen

Question 71

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

Answer 71

25 mmHg | plasma proteins and excess salt

Question 72

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

Answer 72

a coefficient specific for the specific solute

Question 73

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

Answer 73

negative in loose tissue and positive in encapsulated organs

Question 74

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

Answer 74

disruption of the solid phase collagen fibers and proteoglycan gel edema

Question 75

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

Answer 75

negatively-absorption into capillaries

Question 76

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

Answer 76

3 mmHg | drives fluid into tissue and out of capillaries

Question 77

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

Answer 77

arteriole- filtration out of capillary | venule- capillary absorption

Question 78

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

Answer 78

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

Question 79

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

Answer 79

fluid leaving the capillary contains plasma protein

Question 80

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

Answer 80

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

Question 81

how are capillaries different than initial lymphatics?

Answer 81

there are one way valves in lymph vessels

Question 82

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

Answer 82

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

Question 83

what types of diseases cauase edema?

Answer 83

relan, cardiac lung and hepatic diseases

Question 84

what is ascites?

Answer 84

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

Question 85

why can liver disease cause edema?

Answer 85

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