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76 Cards in this Set

  • Front
  • Back
In arterioles, radius and diameter are determined by relative magnitudes of _____ in the vessel lumen and the force of vascular smooth muscle _______.
The effect of vessel radius on wall tension is described by the Law of Laplace where
T =
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)
Arterioles have ____ wall tensions than larger upstream arterial vessels, but ______ wall tensions than smaller downstream microvessels (e.g., capillaries).
________ 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.
Wall tension
In large arteries, wall thickness becomes significant. In those cases, the more appropriate form of the law of Laplace is:  (wall stress) =
P.r/w, where w = wall thickness.
________ 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.
_________ are direct routes from arteriole to venule or venous plexus of skin.
Arteriovenous anastomoses (A.V. Shunts)
_______ DO NOT branch from A.V. shunts
Arteriovenous anastomoses (A.V. Shunts) are located primarily in the ____(cutaneous circulation)
Arteriovenous anastomoses (A.V. Shunts)Function in _______ processes
_______ are Direct route from arteriole to venule
______ branch from metarterioles
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).
True precapillary sphincters are one layer of __________ between smallest (terminal) arterioles or metarterioles and capillaries
smooth muscle
_________ 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.
precapillary sphincters
In the functional sense, ________ also may act as sphincters at the entrance to a capillary bed by constricting or dilating.
terminal arterioles
Capillaries have no smooth muscle. They are composed of only ________ and _________.
endothelial cell
basement membrane
Capillaries are the _____ site of exchange in the vascular system: diffusion of solutes and flow of water occur to and from the surrounding tissues.
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.
surface area
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.
Capillary pore size varies with the ______, e.g., in liver, capillary pores are large, and in skeletal muscle, they are small.
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.
_______ Collect blood from capillary beds.
Venules Participate in the control of distribution of blood _____.
______ of solutes with surrounding tissues via diffusion occurs in the smallest venules, which lack smooth muscle.
blood flow in the microcirculation may be controlled by _____(neural or humoral) and/or _______(local, non-neural) factors.
_____ 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.
Arterioles are under both ____ and ______control
In large Arterioles, only the outer muscle layers appear to be innervated by _______ nerve fibers.
A-V anastomoses are under mainly _____ regulation, under central nervous system control, via sympathetic efferent pathways.
Metarterioles are under both ______ and _____ control
In precapillary sphincters and terminal arterioles, ______ control dominates, but there appears to be some ______ influence.
Capillaries have no ______
smooth muscle
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.
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.
In Venules, ______ control dominates, but there is some ______ influence.
Blood flow through capillary beds is often _______, not continuous
Blood flow through capillary beds results from alternating _______ and ________ of arterioles, metarterioles and precapillary sphincters, closing and opening down-stream capillaries.
The mechanism of vasomotion is probably ______in nature, independent of nerves and hormones. E.g., changes in vessel wall stretch and local chemical concentrations.
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.]
Fick’s law describes simple diffusion:

J =
- PS (Co - Ci), where J = diffusion rate
Capillary permeability (P)
Surface area (S)
Solute concentration difference (Co - Ci)
J is ______ in value when diffusion occurs from inside the capillary to the outside. J is _____ when diffusion is from outside to inside.
permeability is _______ to molecular size
permeability is _______ to lipid solubility
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
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 ____
pores in the endothelium
Diffusion rate is also directly proportional to _______
_____ means net exchange rate of is limited only by how fast it is delivered to the exchange sites by capillary blood flow.
the flow-limited pattern is characteristic of _____, _____- soluble molecules (including oxygen)
_______ means net exchange rate is limited primarily by rate of diffusion across the capillary wall
The diffusion-limited pattern is characteristic of ______, ______-soluble and lipid-insoluble molecules, which diffuse at slower rates
Rate of Tissue Uptake =
= (Ca - Cv) Q

(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.
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.
Surface area

Capillary volume flow
H2O (a small molecule) rapidly diffuses across the capillary walls in both directions. Thus, net exchange of water by diffusion is normally _____.
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.
“bulk flow”
Water moves through _______ channels in endothelial membranes and through inter-endothelial clefts, fenestrae, and endothelial gaps in capillary walls (”pores”).
aquaporin 1
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
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.
. Pc _______ from the arterial to the venous ends of the capillary, because there is a resistance to flow through the capillary
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.
In some vascular beds, the capillary permeability to proteins is great enough to affect _______.
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.
Capillary pressure: Pc is regulated by _______ and _______.
Arterioles: constriction _________ precapillary resistance (Ra), and _______ Pc. This by itself would lead to less filtration and greater absorption. Arteriolar dilation has the opposite effects
Venules: constriction _______ postcapillary resistance (Rv), and _____ Pc. This by itself would lead to greater filtration and less absorption. Venular dilation has the opposite effects.
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.
the fx of the lymphatic system to return to the vascular system any fluid and protein filtered from the _____ but not subsequently reabsorbed.
_________ 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.
Terminal lymphatics
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 ______.
Fluid volume transported per day is about ____ to the total plasma volume
_____ transported per day is about 1/4 - 1/2 of the circulating plasma proteins
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 _______.
3. valves
4. venous
5. filtration
______ formation occurs whenever the rate of net capillary filtration exceeds the rate of lymph drainage, resulting in an increase in
Edema formation can result from Abnormal ________ dynamics:
a. Abnormally high Pc
b. Abnormally low p
c. Lymphatic blockage
d. Increased capillary permeability to proteins
Edema formation can result from abnormal fluid retention by the ______: Pc is elevated.
__________ results in volume expansion and increased central venous pressure elevate Pc. Increased central venous pressure slows return of lymph to central circulation.
Congestive heart failure