Midterm 1 - Blood Volume Microcirculation and Fluid Exchange Flashcards
what percentage of blood do capillaries contain
about 5%
what are capillaries the site of
water-nutrients-wastes-gases exchange with interstitial fluid and tissues
how large are capillaries in diameter
7-8 um
how long are capillaries
0.5 mm
what are red blood cells in diameter
approx. 7.5 um
what are capillaries made of
a single layer of endothelial cells
what are capillaries formed in
dense netowkrs
how close is each cell of a tissue to a capillary
within 100 um
where do capillaries receive blood from
smallest arterioles and metarterioles
metarterioles
connection between arteriole and capillaries network
what does the density of capillaries vary depending on
the metabolic activity of the tissue
what do met arterioles possess
rings of smooth muscle tissue that can open and close on demand
what are met arterioles doing during exercise
all open
what is the consequence of the small diameter
a very slow flow
what is resistance reduced by in capillaries
the extent of the parallel ramifications
what does trans capillary diffusion depend on
capillary type and substance properties
what does transcapillary diffusion follow
gradient between blood and interstitial fluid
what do most capillaries have that allow transfer of water and lipid-insoluble molecules
pores or clefts
what do the size and number of pores in a capillary depend on
the tissue
what type of substances exchange freely across cell membrane
lipid soluble (O2 and CO2)
what capillaries are fenestrated
intestine
liver
kidney
what does it mean for capillaries to be fenestrated
vesicles fuse to form large gaps across endothelial cell membrane
what do fenestrated capillaries allow
water and water soluble macromolecules to pass
what is bulk flow
mass movement of water and dissolves substances through water pores
where does bulk flow take place
across the capillary walls
where is bulk flow filtered
towards interstitial fluid (out of blood compartment)
where is bulk flow absorbed
towards the intravascular fluid (blood)
what does bulk flow maintain
fluid balance between intravascular and interstitial fluid
what is bulk flow dependent on
pressure gradients
permeability of vessel
size of diffusion surface
blood flow
what pressure gradients is bulk flow dependent on
hydrostatic and osmotic
hydrostatic pressure
filtration pressure - BP inside blood vessels pushes fluid out
process of hydrostatic pressure
pressure from heart –> arterioles –> capillaries
since pressure in interstitial fluid is close to 0, pushes fluid out of vessel
what is colloid osmotic pressure (oncotic)
counter balances hydrostatic pressure due to large proteins in that stay in vessel, fluid is reabsorbed
what are starling forces
net movement of fluid depends on balance between filtration (hydrostatic) and osmotic (oncotic) pressures
what pushes fluid out
hydrostatic pressure difference
what pushes fluid back in
osmotic pressure difference
what remains constant along capillary length
osmotic pressure difference
where along the capillary is hydrostatic stronger
in the first portion
where along the capillary does hydrostatic decrease
toward the end - less fluid out, and if hydrostatic < osmotic, fluid moves in
what is the net effect of fluid exchange
generally accumulation of fluid into interstitial tissue
what picks up fluid
lymphatic system
what is lymphatic drainage
the draining of fluid to large veins
what happens to fluid that remains in blood
collects into venues and goes back to heart
what occurs if the lymphatic system cannot keep up with fluid exchange
edema formation (filtration exceeds capacity)
what is the physiological significance of diffusion
nutrient and gas exchange
what is the physiological significance of bulk flow
stabilize blood volume using interstitial fluid as a buffer
physiological significance with blood loss
decrease in pressure –> decrease in hydrostatic = fluid enters back
physiological significance of excess fluid intake
increase in pressure –> increase in hydrostatic –> fluid accumulates in interstitial
physiological significance of low protein in plasma
decrease in ostmotic –> fluid out
physiological significance of high protein in plasma
increase in osmotic –> fluid in
what is an edema
abnormal accumulation of interstitial fluid
what are the 4 mechanisms responsible for edemas
increase in hydrostatic pressure in blood vessels
increase in interstitial protein concentration
decrease in oncotic pressure
obstruction of lymphatic vessels
what can be an effector of increased hydrostatic pressure in blood vessels
increase arterial pressure (hypertension)
increased venous pressure (right sided heart failure)
what can be an effector of increased interstitial protein concentration
inflammation of capillaries, become leaky
what can be an effector of decreased oncotic pressure
loss of proteins (GI disease)
liver disease
poor diet
where do edemas often occur
in abdominal cavity
legs due to gravity
