T551:  Answers to Quiz 2-Capillaries, Veins and Venules, & Lymphatics

1.  concentration gradient

2.  Complete the table below.

* some scientists believe vesicular transport or pinocytosis best explains the transport of large lipid insoluble molecules 

3.  The rate of diffusion is proportional to the surface area available for exchange.  Urea is a lipid soluble compound.  Molecules of urea can diffuse directly through the plasma membrane, the largest area available for exchange.  Albumin is a large lipid insoluble molecule.  It is limited to diffusion through large pores which comprise a very small fraction of the capillary wall.  

4.  Capillaries in different organs are characterized by various types of endothelium.  The endothelium may be continuous or discontinuous or fenestrated.  The permeability of discontinuous or fenestrated endothelium is greater than that of continuous endothelium.

5.  The exchange of oxygen is normally flow-limited.  Its extraction can be increased by an increase in blood flow.  The exchange of larger, lipid insoluble molecules is diffusion limited.  An increase in the surface area available for exchange would increase the diffusion of these molecules.  This might be accomplished increasing the available surface area by capillary recruitment (the opening of additional capillaries) or by an increase in permeability (size or number of pores).

6.  The net movement of water across the capillary is determined by the balance between hydrostatic and oncotic pressures in the capillary and interstitium.  Normally, the greatest force for filtration (movement of water from the capillary to the tissue) is the capillary hydrostatic pressure; and the largest force for absorption (movement from the tissue to capillary) is the plasma oncotic pressure.  Tissue oncotic and hydrostatic pressures  also influence the net movement of water.

         Normally, the major change in these forces from the arteriolar to venular end of the capillary would be a decrease in capillary hydrostatic pressure.

 7.  Tell whether the conditions below would favor filtration or absorption and list the altered force and or factor responsible for the change. 

8.  Anchoring filaments attached to the abluminal lymphatic wall and tethered in the interstitium prevent the lymphatic capillaries from collapsing during edema.

9.  Pressures in lymphatics and veins are low and may cycle such that at times the upstream pressure could be greater than the downstream pressure.  This could cause the flow of fluid in these vessels to revers.  Normally functioning valves prevent the reflux or retrograde movement of lymph and blood in lymphatics and veins.

10.  The primary function of the lymphatic system is to return to the veins the plasma proteins which are able to cross the capillary membrane into the tissues.  The concentration gradient prevents net diffusion of the proteins back into the capillary.  The lymphatic system also is important in preventing edema during times of excess fluid filtration.

11.  Complete the chart below indicating what effect each of the following would have on total blood volume (TBV), venous volume (Vv), end diastolic volume of the heart (EDV), and cardiac output (CO).  ¯ = decrease;  > =  increase, ------- = no immediate change

12.  Venous pressure in the lower limbs is normally reduced when walking by the action of the skeletal muscle pump.  This propels venous blood forward, reducing venous pooling and decreasing venous pressure.  

13.  The net filtration force is capillary pressure plus tissue oncotic pressure (35+3=38).  The net absorptive force is plasma oncotic pressure plus tissue hydrostatic pressure (38+0=38).  The net force for fluid movement is zero.

 

Teaching Activities-T551

T551: Quiz 1

T552: Quiz 3

Copyright © 1999 Joseph L. Unthank

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