Term
How do gases cross capillaries?
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Definition
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Term
| What is a tissue cylinder? |
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Definition
| the area around a capillary to which the capillary supplies O2 |
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Term
6 factors that affect PO2within a capillary |
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Definition
1. amount of O2 in blood entering capillary
2. capillary blood flow
3. radial diffusion coefficient
4. capillary radius
5. radius of tissue cylinder
6. axial distance along capillary
bold = highlighted in lecture |
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Term
| What two factors matter most for the O2 extraction ratio in a whole organ? |
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Definition
| capillary blood flow and oxygen consumption |
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Term
| What is an extraction ration? |
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Definition
| the percent of the oxygen content that an organ removes from the blood |
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Term
| What effect will decreasing the blood flow have on extraction coefficient? |
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Definition
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Term
| What effect will decreasing the metabolic demand have on the extraction coefficient? |
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Definition
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Term
What effect will increasing the number of active capillaries have on PO2 ?
(i.e., skeletal muscle response to exercise) |
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Definition
increases blood flow and increases capillary surface area/decreases tissue radius
causes PO2 in tissue to increase |
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Term
| In relation to length and radius of capillary, where is the PO2 highest? Lowest? |
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Definition
highest: arterial end and close to center of capillary
lowest: venous end and further from center of capillary |
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Term
Two factors that affect diffusion of small water soluble solutes across a capillary wall
(fick's law) |
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Definition
concentration gradient
permeability coefficient (diffusion coefficient and wall thickness) |
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Term
| What signals precapillary sphincters? |
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Definition
Molecules in ECF like H+, O2 and CO2
not controlled by autonomic |
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Term
| Which end of a capillary has the greatest permeability? |
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Definition
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Term
| Examples of where to find continuous capillaries |
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Definition
| muscles, bones and exocrine (since exocrine secretions are technically outside of body) |
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Term
| Examples of where to find fenestrated capillaries |
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Definition
endocrine, renal and small intestines
places that need to allow protein through (ie hormone distribution, nutrient absorption...) |
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Term
| Examples of where to find sinusoidal/discontinuous capillaries |
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Definition
| liver, bone marrow and spleen |
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Term
| Which organ has capillaries that lack a true basement membrane? |
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Definition
Liver
alcoholism/fibrosis can lead to formation of BM |
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Term
How can capillary surface area increase in an organ?
How can the permeability coefficent increase? |
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Definition
-SA can increase if precapillary sphincters relax
- Px can increase during inflammation (cytokines, histamines) |
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Term
| True or False: the permeabilty coefficent and capillary surface are are constant within an organ |
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Definition
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Term
| How do small polar molecules cross capillary walls? |
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Definition
| diffusion through paracellular pathways |
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Term
Which end of the capillary has more fenestrae and wider clefts?
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Definition
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Term
| What role does the glycocalyx play in microfiltration? |
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Definition
| it acts a barrier in the clefts to exclude large/negative marcomolecules |
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Term
| How do large macromolecules cross capillary walls? |
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Definition
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Term
| What factor dictates how permeable the capillary wall membranes are to large molecules? |
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Definition
Size of molecule/ sieving
large molecules are less permeable
small are more permeable |
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Term
| What are Starling forces? |
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Definition
| forces that determine flux of water across capillaries |
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Term
| What is the main mechanism for transfer of fluid across capillary wall? What are the two driving forces? |
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Definition
Convection
hydrostatic pressure difference (ΔP)
onconic pressure different (Δπ)
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Term
| What causes onconic pressure inside the capillary? Outside? |
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Definition
inside: plasma proteins
outside/if: interstitial proteins and proteoglycans |
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Term
| What does a postive Jv value mean? |
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Definition
| flux out of the capillary |
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Term
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Definition
reflection coefficient
π observed/ π theoretical
capillary walls excludes proteins imperfectly, this measures how much it is excluded
ranges from 0-1
0= not excluded at all
1= completely excluded, doesn't cross |
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Term
| In general, what are the net filtration pressure at the arterial and venous ends? |
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Definition
arterial: positive= filtration
venous: negative= absorption |
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Term
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Definition
1. upstream and downstream pressure
2. location in body (ie. eyes and glomueral are high)
3. time
4. gravity (higher below heart) |
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Term
| Where will Pif have a positive value? |
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Definition
| encapsulated organs and rigid enclosed compartments |
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Term
πc is determined primarily by ________ composition.
Increasing _________ will cause an increase in πc |
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Definition
plasma proteins
lower MW proteins/alpha1 globulin and albumin |
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Term
| What effect does the Donnan effect have on πc? |
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Definition
it increases it
without it πc would be lower (16-18 mmHg) |
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Term
In starling's equation, which two forces are relatively constant along length of capillary?
which two are dynamic? |
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Definition
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Term
Where does the net filtration pressure switch from + to - along the lenght of a capillary?
Significance? |
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Definition
about 3/4
this is why all fluid that is filtered isn't reabsorbed |
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Term
At the venous end _______ pressure typically dominates.
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Definition
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Term
| At the arterial end _________ pressure typically dominates |
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Definition
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Term
| Why are observed filtration and absorption rates different from what starling hypothesized? |
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Definition
| he didn't account for the gycocalyx or differences in onconic and hydrostatic pressures in the clefts compared to the interstiutium |
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Term
During ultrafiltration:
Psg is _________than Pif
and
πsg is _________ than πif |
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Definition
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