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25 Cards in this Set
- Front
- Back
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1. Describe capillaries.
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1. Smallest vessels in cardiovascular system
2. Comprised of single layer of endothelial cells 3. Cannot constrict or dilate |
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2. What are involved in regulation of TPR and local blood flow?
What regulates the distribution of blood flow among capillaries? What is special about postcapillary venules? |
Small arteries and arterioles
Terminal arterioles and in some tissues pre-capillary sphincters Devoid of smooth muscle and are an important area of exchange |
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3. What can significantly influence capillary hydrostatic pressure?
How is the morphology of the microvascular bed? What is the density of exchange vessels proportional to? |
Alterations in postcapillary resistance and pressure
Varies among tissues - meet specific needs of a tissue Proportional to the metabolic requirements of the tissue |
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4. What are two functional characteristics of the microcirculation?
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1. Capillary blood flow is often intermittent and may change direction
2. RBCs must fold and pass in single file through capillaries |
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5. What are some types of control that control blood flow through the microcirculation?
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1. Neural control
2. Hormonal control 3. Local control -metabolic -myogenic -endothetial control 4. Summated effects of all above factors |
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6. What is the primary innervation for neuronal control?
Where does this control have the most pronounced effects? What is the neural innervation primarily involved in? What do the neural innervation probably have little influence over? |
Primary innervation by sympathetic nerves
Most pronounced effect is on small arteries and arterioles Primarily involved in regulation of systemic blood pressure Sympathetics have little influence over the terminal arterioles and precapillary sphincters |
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7. What effect does hormonal control have?
What are some examples? |
Number of vasoactive hormones affect the diameter of the arterial vessels
1. Epinephrine from adrenal medulla 2. Angiotensin II (vasoconstrictor) |
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8. What can the byproducts of tissue metabolism cause?
What does this result in? |
Cause the vascular smooth muscle to relax and the vessels to dilate
Provides a coupling mechanism between local tissue need and local blood flow |
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9. What do changes in transmural pressure influence?
(myogenic control) What does increasing the transmural pressure result in? What does decreasing it cause? |
The degree of contraction of smooth muscle cells surrounding the arterial microvessels
Increasing - vessels constrict Decreasing - vessels dilate |
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10. What do endothelial vessels release?
What is the final determinant of the diameter of the precapillary resistance vessels? |
Release both vasoconstrictors and vasodilators
Summated effects of all the previously mentioned factors **these factors may work in opposition |
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11. What does the sensitivity of a given vessel to each of the previous factors depend upon?
What are the terminal arterioles predominantly influenced by? What are they less influenced by? |
Sensitivity varies w/ location of vessel in vascular tree and among the various organs
More influenced by metabolic and myogenic mechanism Less influenced by neural control than are the small arteries and arterioles |
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12. Why are capillaries and postcapillary venules the primary site of exchange across the circulation?
(three reasons) |
1. Extremely thin walls
2. Composed of a single layer of endothelial cells 3. Large surface areas |
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13. What are some of the possible pathways for transport across the capillary endothelium?
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1. Diffusion
-lipid soluble substances (O2, CO2) 2. Bulk flow -electrolytes, small molecules, H2O 3. Vesicles -macromolecules 4. Active transport -ions, small molecules |
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14. How does the rate of diffusion of water back and forth across the capillaries compare to the rate of filtration and absorption?
How do the majority of dissolved gas and nutrient molecules move across the capillaries? What does Frick's Law govern? |
Rate of diffusion is 4,000 times the rate of filtration and absorption
Diffusion There is a net transfer of molecules from areas of high concentration to areas of low concentration |
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15. Where can lipophilic substances diffuse?
Where is the diffusion of lipid-insoluble molecules restricted to? How is the amount of restriction related to the molecular size? |
Have entire capillary surface area available for diffusion
Restricted to "pores" in the capillaries Amount of restriction increases in proportion to the molecular size |
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16. How much of the plasma passing through the capillaries is filtrated?
What is the amount of fluid filtered important to? What determines the magnitude of filtration and absorption by the capillaries? |
Only a small fraction (1-2%)
Regulation of blood and interstitial fluid volume Determined by the hydrostatic and osmotic pressures existing across the capillary wall |
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17. What factors favor filtration?
What factors favor absorption? |
Filtration:
1. Capillary hydrostatic pressure 2. Tissue colloid osmotic pressure Absorption 1. Plasma protein oncotic pressure (colloid osmotic pressure) 2. Tissue hydrostatic pressure |
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18. Where is the concentration of protein the greatest and why?
How does this affect plasma osmotic pressure? |
Greater in the plasma than in the interstitial fluid b/c the capillaries are relatively impermeable
Higher [protein] causes plasma osmotic pressure to be approx 25 mm Hg higher than interstitial fluid osmotic pressure |
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19. What are the effects of disturbances in the starling capillary forces on ultrafiltration?
1. Arteriolar dilation 2. Arteriolar constriction 3. Increased venous pressure 4. Dehydration 5. Hypoproteinemia |
1. Increase filtration, decrease absorption
2. Decrease filtration, increase absorption 3. Increase filtration, decrease absorption 4. Decrease filtration, increase absorption 5. Increase filtration, decrease absorption |
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20. Do all capillaries have the same hydrostatic pressure?
What does this result in? In areas where capillaries have low hydrostatic pressure what happens to the interstitial fluid pressure? |
No
Therefore: 1. Some capillaries filter fluid along their entire length 2. Other capillaries may reabsorb along their entire length Interstitial fluid pressure may actually be negative |
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21. What factors influence capillary hydrostatic pressure?
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1. Systemic arterial pressure
2. Precapillary resistance 3. Postcapillary resistance 4. Venous pressure |
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22. What does increasing resistance do to pressure?
What factors influence tissue hydrostatic pressure? |
Elevates pressure upstream and reduces pressure downstream
1. Interstitial fluid volume 2. Compliance of the interstitial space |
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23. What does the osmotic pressure gradient across the capillary wall depend upon?
What can an imbalance between the forces causing filtration and those causing absorption result in? How is the interstitial fluid under normal conditions? What happens though when edema occurs? |
1. Plasma protein concentration
2. Tissue protein concentration Edema formation Interstitial fluid is contained in a gel w/ no bulk flow of free fluid Bulk flow of fluid can occur in interstitium |
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24. What is the major function of the lymphatic system?
What is the lymphatic system the only mechanism for? Why can lymph flow be increased by 20 fold? |
Return interstitial fluid and plasma proteins into the blood
Only mechanism for a net transport of plasma proteins into the blood Increased 20 fold in order to compensate for an increase in filtration |
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25. What collects interstitial fluid?
How is lymph propelled through the lymphatic system? What facilitates this process? |
Terminal lymphatic capillaries
By spontaneous contractile activity of the lymphatic vessels and by intermittent skeletal muscle contractions Presence of one-way valves |
