Microcirculation

Front 1

In arterioles, radius and diameter are determined by relative magnitudes of _____ in the vessel lumen and the force of vascular smooth muscle _______.

Back 1

pressure
contraction

Front 2

The effect of vessel radius on wall tension is described by the Law of Laplace where
T =

Back 2

P.r (assumes vessel is shaped as a cylinder.)

where T = wall tension
P = intraluminal pressure
r = vessel radius
(wall thickness is assumed to be negligible in this case)

Front 3

Arterioles have ____ wall tensions than larger upstream arterial vessels, but ______ wall tensions than smaller downstream microvessels (e.g., capillaries).

Back 3

lower
greater

Front 4

________ is the force which a vessel’s wall structure must withstand in order to prevent the vessel from rupturing. Small radii of microvessels allow them to withstand their respective intraluminal pressures, despite very thin walls. The latter is especially true for capillaries.

Back 4

Wall tension

Front 5

In large arteries, wall thickness becomes significant. In those cases, the more appropriate form of the law of Laplace is:  (wall stress) =

Back 5

P.r/w, where w = wall thickness.

Front 6

________ participate in local control of blood flow, and also control of systemic arterial and capillary pressures. Some exchange with surrounding tissues by diffusion is possible in the smallest ones with the thinnest walls.

Back 6

Arterioles

Front 7

_________ are direct routes from arteriole to venule or venous plexus of skin.

Back 7

Arteriovenous anastomoses (A.V. Shunts)

Front 8

_______ DO NOT branch from A.V. shunts

Back 8

Capillaries

Front 9

Arteriovenous anastomoses (A.V. Shunts) are located primarily in the ____(cutaneous circulation)

Back 9

skin

Front 10

Arteriovenous anastomoses (A.V. Shunts)Function in _______ processes

Back 10

thermoregulatory

Front 11

_______ are Direct route from arteriole to venule

Back 11

Metarterioles

Front 12

______ branch from metarterioles

Back 12

Capillaries

Front 13

Metarteries function to control flow to the capillary beds when precapillary sphincters are _____(nutritional flow), or bypass the capillary beds when precapillary sphincters are ____ (shunt flow).

Back 13

open
closed

Front 14

True precapillary sphincters are one layer of __________ between smallest (terminal) arterioles or metarterioles and capillaries

Back 14

smooth muscle

Front 15

_________ Function to control the number of open capillaries (“capillary density”), capillary blood flow and capillary pressure. i.e., closure of precapillary sphincters will result in the closure of entire segments of a capillary bed, thus reducing capillary blood flow and capillary pressure in these segments.

Back 15

precapillary sphincters

Front 16

In the functional sense, ________ also may act as sphincters at the entrance to a capillary bed by constricting or dilating.

Back 16

terminal arterioles

Front 17

Capillaries have no smooth muscle. They are composed of only ________ and _________.

Back 17

endothelial cell
basement membrane

Front 18

Capillaries are the _____ site of exchange in the vascular system: diffusion of solutes and flow of water occur to and from the surrounding tissues.

Back 18

primary

Front 19

In capillaries, A large _______ for exchange is created within a relatively small volume, because capillaries have very small diameters and there are very large numbers of them.

Back 19

surface area

Front 20

Solutes ______ through endothelial membranes or through capillary “pores” (inter-endothelial clefts, fenestrae, or endothelial gaps). Numbers of pores _______ from arterial to venous ends of capillaries.

Back 20

diffuse
increase

Front 21

Capillary pore size varies with the ______, e.g., in liver, capillary pores are large, and in skeletal muscle, they are small.

Back 21

tissue

Front 22

In the brain, capillary pores are absent in most areas, making these capillaries impermeable to ________ solutes. This is partially the basis of the “blood-brain barrier” to such solutes.

Back 22

lipid-insoluble

Front 23

_______ Collect blood from capillary beds.

Back 23

Venules

Front 24

Venules Participate in the control of distribution of blood _____.

Back 24

volume

Front 25

______ of solutes with surrounding tissues via diffusion occurs in the smallest venules, which lack smooth muscle.

Back 25

Exchange

Front 26

blood flow in the microcirculation may be controlled by _____(neural or humoral) and/or _______(local, non-neural) factors.

Back 26

extrinsic
intrinsic

Front 27

_____ control is thought to be the result of chemical substances produced by or consumed by the tissues, and which affect the contraction of vascular smooth muscle.

Back 27

local

Front 28

Arterioles are under both ____ and ______control

Back 28

neural
local

Front 29

In large Arterioles, only the outer muscle layers appear to be innervated by _______ nerve fibers.

Back 29

autonomic

Front 30

A-V anastomoses are under mainly _____ regulation, under central nervous system control, via sympathetic efferent pathways.

Back 30

neural

Front 31

Metarterioles are under both ______ and _____ control

Back 31

neural
local

Front 32

In precapillary sphincters and terminal arterioles, ______ control dominates, but there appears to be some ______ influence.

Back 32

local
neural

Front 33

Capillaries have no ______

Back 33

smooth muscle

Front 34

In capillaries, no active changes in diameter are thought to occur, despite actin and myosin filaments in endothelial cells. Flow into capillary beds and the numbers of open capillaries are influenced by the metarterioles and precapillary sphincters upstream. Thus, changes in capillary diameter are ______, in response to changes in transmural pressure.

Back 34

passive

Front 35

Generally, capillary permeability is not under direct control. However, there is some evidence that _______ and ________ may increase permeability of capillaries in some (not all) tissues.

Back 35

norepinephrine
histamine

Front 36

In Venules, ______ control dominates, but there is some ______ influence.

Back 36

neural
local

Front 37

Blood flow through capillary beds is often _______, not continuous

Back 37

intermittent

Front 38

Blood flow through capillary beds results from alternating _______ and ________ of arterioles, metarterioles and precapillary sphincters, closing and opening down-stream capillaries.

Back 38

constriction
dilation

Front 39

The mechanism of vasomotion is probably ______in nature, independent of nerves and hormones. E.g., changes in vessel wall stretch and local chemical concentrations.

Back 39

local

Front 40

Most small solutes are exchanged between capillaries and surrounding tissues primarily by simple _______ (including gases, substrates and metabolic “waste” products). Normally, only small amounts of solutes are exchanged across capillary walls by carrier-mediated mechanisms or vesicular transport. [Large quantities of H2O also diffuse across the capillary walls, in both directions equally, with little net exchange by this mechanism.]

Back 40

diffusion

Front 41

Fick’s law describes simple diffusion:

J =

Back 41

- PS (Co - Ci), where J = diffusion rate
Capillary permeability (P)
Surface area (S)
Solute concentration difference (Co - Ci)

Front 42

J is ______ in value when diffusion occurs from inside the capillary to the outside. J is _____ when diffusion is from outside to inside.

Back 42

positive
negative

Front 43

permeability is _______ to molecular size

Back 43

inversely

Front 44

permeability is _______ to lipid solubility

Back 44

perportional

Front 45

Surface area (S) for diffusion also depends on the nature of the substance. For lipid-soluble substances, surface area is equal to the total surface area of ____ capillaries

Back 45

open

Front 46

Surface area (S) for diffusion also depends on the nature of the substance. For lipid insoluble substances, surface area is equal to the total surface area of ____

Back 46

pores in the endothelium

Front 47

Diffusion rate is also directly proportional to _______

Back 47

temperature

Front 48

_____ means net exchange rate of is limited only by how fast it is delivered to the exchange sites by capillary blood flow.

Back 48

flow-limited

Front 49

the flow-limited pattern is characteristic of _____, _____- soluble molecules (including oxygen)

Back 49

small
lipid

Front 50

_______ means net exchange rate is limited primarily by rate of diffusion across the capillary wall

Back 50

diffusion-limited

Front 51

The diffusion-limited pattern is characteristic of ______, ______-soluble and lipid-insoluble molecules, which diffuse at slower rates

Back 51

large
water

Front 52

Rate of Tissue Uptake =

Back 52

= (Ca - Cv) Q

Where
(Ca - Cv) = arteriovenous concentration difference of the solute.
Ca = capillary blood solute concentration at the arterial end of capillary.
Cv = capillary blood solute concentration at the venous end of capillary.
Q = volume flow of blood through the tissue under examination.

Front 53

Exchange by diffusion can be controlled to some extent.
________ is controlled by precapillary sphincters, which determine the number of open capillaries.
__________, which affects rate of solute delivery to tissues or rate of solute removal from tissues, is controlled primarily by upstream arterioles.

Back 53

Surface area

Capillary volume flow

Front 54

H2O (a small molecule) rapidly diffuses across the capillary walls in both directions. Thus, net exchange of water by diffusion is normally _____.

Back 54

small

Front 55

In addition, there is a relatively slow rate of water exchange across capillary walls by _______. This is the result of a different mechanism, filtration-absorption.

Back 55

“bulk flow”

Front 56

Water moves through _______ channels in endothelial membranes and through inter-endothelial clefts, fenestrae, and endothelial gaps in capillary walls (”pores”).

Back 56

aquaporin 1

Front 57

The following forces are involved in producing _________:

1. Capillary “hydrostatic” pressure (Pc)
2. Interstitial fluid pressure (Pi)
3. Plasma colloid osmotic pressure (p), due to plasma proteins
4. Interstitial fluid colloid osmotic pressure (i), due to interstitial fluid proteins

Back 57

filtration-absorption

Front 58

By convention, capillary “hydrostatic” pressure is the ____ of the blood pressure due to the pumping action of the heart and any P = hg due to gravity at the specific location of the capillaries being considered.

Back 58

sum

Front 59

. Pc _______ from the arterial to the venous ends of the capillary, because there is a resistance to flow through the capillary

Back 59

decreases

Front 60

Pc depends on arterial pressure (Pa), venous pressure (Pv) and on resistances of precapillary and postcapillary vessels (Ra and Rv, respectively): An increase in Pa, Pv, or Rv alone would ______ Pc, provided Ra does not increase. An increase in Ra alone _______ Pc. The opposite occur in response to decreases in Pa, Pv, Rv and Ra.

Back 60

increase
decreases

Front 61

In some vascular beds, the capillary permeability to proteins is great enough to affect _______.

Back 61

filtration-absorption

Front 62

In such cases, the plasma and interstitial fluid oncotic pressures would be _______ by the capillary walls’ reflection coefficient for proteins (). The value of  (between 0 and 1) is inversely proportional to the permeability of the capillary walls to protein molecules, so s = 1 is complete impermeability.

Back 62

multiplied

Front 63

Capillary pressure: Pc is regulated by _______ and _______.

Back 63

arterioles
venules

Front 64

Arterioles: constriction _________ precapillary resistance (Ra), and _______ Pc. This by itself would lead to less filtration and greater absorption. Arteriolar dilation has the opposite effects

Back 64

increases
decreases

Front 65

Venules: constriction _______ postcapillary resistance (Rv), and _____ Pc. This by itself would lead to greater filtration and less absorption. Venular dilation has the opposite effects.

Back 65

increases
increases

Front 66

When pre- and post-capillary resistances and surface area changes occur simultaneously, the net effect on filtration-absorption depends on the algebraic ____ of these changes.

Back 66

sum

Front 67

the fx of the lymphatic system to return to the vascular system any fluid and protein filtered from the _____ but not subsequently reabsorbed.

Back 67

capillaries

Front 68

_________ are closed-ended, highly permeable vessels which appear much like capillaries. They are anchored to the surrounding connective tissue by filaments, which effectively hold the lymphatic pores open.

Back 68

Terminal lymphatics

Front 69

Lymph “capillaries” empty into larger lymphatic vessels, which finally drain into the venous system (at junctions of the subclavian and internal jugular veins). Large lymphatic vessels have an extensive system of one-way valves to keep flow going toward the central systemic ______.

Back 69

veins

Front 70

Fluid volume transported per day is about ____ to the total plasma volume

Back 70

equal

Front 71

_____ transported per day is about 1/4 - 1/2 of the circulating plasma proteins

Back 71

Protein

Front 72

Factors influencing the rate of lymph flow:

1. Tissue _____
(influenced by degree of skeletal muscle activity).
2. Contractions of lymph vessels.
3. One way _____in lymph vessels.
4. Central _____ pressure (similar to right atrial pressure).
5. Anything which affects the rate of net capillary _______.

Back 72

1.pressure
2.
3. valves
4. venous
5. filtration

Front 73

______ formation occurs whenever the rate of net capillary filtration exceeds the rate of lymph drainage, resulting in an increase in

Back 73

Edema

Front 74

Edema formation can result from Abnormal ________ dynamics:
a. Abnormally high Pc
b. Abnormally low p
c. Lymphatic blockage
d. Increased capillary permeability to proteins

Back 74

capillary

Front 75

Edema formation can result from abnormal fluid retention by the ______: Pc is elevated.

Back 75

kidneys

Front 76

__________ results in volume expansion and increased central venous pressure elevate Pc. Increased central venous pressure slows return of lymph to central circulation.

Back 76

Congestive heart failure