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physiology IV > Microcirculation > Flashcards

Flashcards in Microcirculation Deck (21):

At high or low flow rates does blood behave anomalously?

Low flow rates - formation of rouleauxs
-inc viscosity


What is polycythemia ?

abnormal increase in RBCs
-viscosity and resistance double


How does hematocrit affect viscosity?

-low hemat - inc bc of stickiness
-high hemat -inc bc of cell deformation


How does vessel radius affect viscosity?

-relatively insensitive for large vessels
-decreases steeply with dec in radius for small vessels

-this occurs because of axial streaming


What is a rouleaux?

chain like aggregates of RBCs which form at low flow rates


Where are continuous capillaries present?

Skeletal muscle


Where are fenestrated capillaries present?

Exocrine glands or epithelial membranes


Where are discontinuous capillaries present?

Liver sinusoids


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

1. change in flow rate
2. change in arterial concentration


What four factors determine the diffusion rate of a substance btwn blood and interstitial fluid?

1. concentration difference
2. Surface area
3. Permeability
--these are all directly correlated with diffusion rate
4. Diffusion distance
--indirectly correlated


What are net shifts in fluid btwn capillary and interstital compartments important for?

-maintenance of blood volume
-fluid absorption
- edema
-saliva and sweat production
-urine production


What are the four pressures that control transcapillary fluid movement and what are their aproximate values?

1. Capillary hydrostatic ~25
-directed out of vessel
2. interstial hydrostatic pressure ~0
3. capillary osmotic pressure
-directed into vessel
4. Interstital osmotic pressure ~3
-directed out of vessel


In which way is the transcapillary fluid movement a positive value ?(Jv)

-from capillaries to interstitium


What happens to capillary hydrostatic pressure down it's length?

It drops - venule end has lower hydrostatic pressure than arteriole end


What occurs as a result of arteriolar dilation or venular constriction?

-Filtration - movement out of capillaries


What occurs as a result of ateriolar constriction or venular dilation ?

Fluid reabsorption - movement into capillaries


What is the Pif in loose tissues? in rigid closed compartments?

Loose - negative
-drives filtration
Closed - positive
-drives absorption


Ignoring the rate in the kidneys, does a higher rate of filtration or absorption occur throughout the capillaries? What is an aprox value for the net rate?

-Net filtration of 2-4 L/day


Describe the process by which lymph enters lymphatics

Expansion phase
1. Hydrostatic P in interstitium > initial lymphatic
2. Microvalves open and fluid enters

Compression phase
3. Hydrostatic P inside the initial lymphatic rises closing the microvalves
4. Opens secondary lymph valves – flow downstream


Where do the large lymphatics drain into?

R and L subclavian veins


Does filtration or absorption occur at arteriolar ends? venular ends?

arteriolar - filtration
venular - absorption