Flashcards in Microcirculation Deck (21)
At high or low flow rates does blood behave anomalously?
Low flow rates - formation of rouleauxs
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?
Where are fenestrated capillaries present?
Exocrine glands or epithelial membranes
Where are discontinuous capillaries present?
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
--these are all directly correlated with diffusion rate
4. Diffusion distance
What are net shifts in fluid btwn capillary and interstital compartments important for?
-maintenance of blood volume
-saliva and sweat 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
Closed - positive
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
1. Hydrostatic P in interstitium > initial lymphatic
2. Microvalves open and fluid enters
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