Microcirculation

Question 1

Define Anomalous viscosity:

Answer 1

It is an increase in viscosity at low flow rate. At high speed blood acts newtonian but at low speed blood viscosity becomes important.

Question 2

Is the flow-pressure curve of blood linear? Why?

Answer 2

It is nonlinear. At low flow rates blood appears to have a higher resistance than at faster flow rates due to formation of Rouleaux. As blood flow increases, Rouleaux rend to break up, thereby decreasing the viscosity and resistance, thus contributing to anomalous viscosity.

Question 3

What is the Fahraeus-Lindqvist effect?

Answer 3

It is that the apparent viscosity of blood depends on the diameter of the tube through which it is flowing. A tube diameter less than .3mm (arterioles, capillaries, venues) the apparent viscosity of blood decreases.

Question 4

At high hematocrits what happens to viscosity and why?

Answer 4

Viscosity increases because of cell deformation

Question 5

What explains the low blood viscosity in tubes of small diameter?

Answer 5

Axial streaming (plasma skimming), the tendency of red cells to accumulate in the rapidly flowing axial lamina. The result is lower hematocrit in the smaller vessel. (think of escalator example)

Question 6

What are nonideal rheological effects? Rheology is the study of fluids.

Answer 6

1-formation of Rouleaxu
2-Axial streaming; plasma skimming
3-Cellular deformability
4-Fahraeus-Lindqvist effect
Blood is a non-Newtonian fluid meaning it doesn't have a constant viscosity

Question 7

Precapillary sphincters control local flow within the capillary network, are they innervated? How do they work?

Answer 7

No they are not. They are responsive to local conditions of oxygen, CO2, and acidity. They are extremely sensitive to hypoxia.

Question 8

What is the formula for calculating cardiovascular transport?

Answer 8

Transport of X=Flow rate x Concentration of X. Or X=Qx[C].

Question 9

What are the only two methods to alter the rate at which a substance is carried to an organ?

Answer 9

1 Change the flow rate through the organ. 2 Change the arterial concentration of X.

Question 10

What is the Fick principle? How is it calculated?

Answer 10

Tissue rate of utilization of production of substance X measured from transport rate IN and OUT of the tissue. Trasncapillary efflux rate (mass/time) = Q x ([X_arterial - X_venous]).

Question 11

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

Answer 11

The tissue is producing it.

Question 12

What are the four factors that determine the diffusion rate of a substance between blood and interstitial fluid?

Answer 12

1 Concentration difference
2 Surface area for exchange (maximized by capillaries)
3 diffusion distance (constant usually)
4 Permeability of the capillary wall to the diffusion substance (regulated)

Question 13

What is the formula for Fick’s law of diffusion?

Answer 13

J = DA (C_p - C_i)/ l
J=flux (moles/sec) D=diffusion coefficient (cm/sec) characteristic of the solute and membrane. A=area of membrane (cm^2) l=thickness of membrane (cm). C=concentration (moles/cm^3) in plasma and interstitial fluid.

Question 14

What is the formula for transcapillary fluid movement?

Answer 14

P_net= (P_c - P_if) - (π_c - π_if)

where; P=hydrostatic pressure and π=osmotic pressure.

Question 15

How do gases and other small solutes cross the capillary membrane? How does water?

Answer 15

Diffusion. Water does it by convection.

Question 16

What is Starling’s equation for capillary flow?

Answer 16

J_v=L_p x [(P_c - P_if) - (π_c - π_if)]
J_v=net capillary filtration flow rate (ml/cm^2sec)
L_p=hydraulic conductivity (ml/cm^2sec)/mmHg
Convective water movement is driven by the difference in the hydrostatic pressure and by the difference in osmotic pressure across the capillary muscle.

Question 17

If J_v is positive what does that mean? What about negative?

Answer 17

Flows from the capillaries to the interstitial fluid have positive J_v.

Question 18

What effect does a positive hydrostatic pressure difference have (with respect to Starling equation and capillary flow)?

Answer 18

∆P=P_c-P_i . Drives a positive flow of water out of the capillaries into the interstitial fluid.

Question 19

What effect does a positive osmotic pressure pressure difference have (with respect to Starling equation and capillary flow)?

Answer 19

∆π=π_c-π_i . Drives a negative flow of water into the capillaries from the interstitial fluid space.

Question 20

What does a higher Capillary hydrostatic pressure (P_c) favor?

Answer 20

Filtration. P_c falls linearly along the length of a capillary and its average is in the middle of it. Normally it is about 25mmHg. It is also, like other blood pressures, influenced by gravity.

Question 21

What can arterioles and venues do to increase capillary hydrostatic pressure?

Answer 21

Arteriolar dilation or venular constriction.

Question 22

What can arterioles and venues do to decrease capillary hydrostatic pressure?

Answer 22

Arteriolar constriction or venular dilation

Question 23

What is the main effector of colloid osmotic pressure?

Answer 23

Protein concentration (plus the excess salt caused by the Gibbs Donnan effect exerted by the proteins).

Question 24

What effect does a negative interstitial fluid hydrostatic pressure have (π_if)? Positive?

Answer 24

Negative exerts a force that drives fluid filtration (lung and subcutaneous tissue). Positive exerts a force that drives fluid absorption (bone, kidney, skeletal muscle)

Question 25

What is the total body average π_if?

Answer 25

3mmHg exerting a force that drives filtration.

Question 26

Starling equation predicts _____ at the arteriolar end and ______ at the venular end of most capillary beds/

Answer 26

Filtration; absorption. (remember that Pc falls along the length of the capillary)

Question 27

Plasma albumin is synthesized in the liver and secreted into the plasma what can happen during liver disease?

Answer 27

Hypoalbuminemia and peripheral edema.

Question 28

What is SIADH? What can it cause?

Answer 28

Inappropriate secretion of antidiuretic hormone by certain lung tumors. It can lead to peripheral edema.