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microcirculation
CVM
24
Medical
Graduate
03/10/2010

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Cards

Term
who was the first person to describe capillaries?
Definition
marcello malpighi
Term
what is the major determinant of resistance? how is this manifested in capillaries? how is this overcome in capillaries?
Definition
radius - capillaries have a very small radius and therefore high resistance, however this is spread out over a huge cross-sectional area, so resistance in total is lower
Term
what is the major mechanism for exchange of exchange of materials in the body?
Definition
diffusion down a concentation gradient - distances for this are very low, so a tremendous amount of exchange occurs over the length of a capillary
Term
what is the movement of fluid in response to the net hydrostatic and osmotic forces across the capillary endothelium?
Definition
filtration and absorption, the minor means of exhanging materials in the body
Term
what is the rate of diffusion determined by?
Definition
the concentration gradient (higher = faster), which is the concentration difference of a substance between 2 sides of a membrane
Term
what is an example of a concentration gradient in the human body?
Definition
the concentration of oxygen is higher in capillary blood than interstitial fluid, allowing O2 to move to the tissues. CO2 is higher in these tissue than in the capillary blood, and can therefore diffuse out
Term
what is the major way of controlling blood pressure?
Definition
arterioles are surrounded by a thick coat of smooth muscle and are under hormonal control
Term
what does the arteriole divide into?
Definition
arterioles divide ~5x into metarterioles, which are inbetween arterioles and capillaries. they have intermittent smooth muscle and divide 5-8x before they reach the structure of a capillary
Term
what is a pre-capillary sphincter?
Definition
a patch of smooth muscle that controls the flow down the structure of the capillary
Term
what do capillaries eventually become?
Definition
venules, which have sparse patches of smooth muscle (which works b/c not much muscle is needed to contract these vessels - as venules become larger vessels, more smooth muscle is seen and compliance goes down)
Term
how many cells thick is a capillary? what is their diameter?
Definition
capillaries have 1 cell thick walls and are about 1/2 a micron in diameter
Term
where do most of the exchanges occur in capillaries?
Definition
in the intracellular cleft, the gap between cells - the size of which is 50-90 nm (smaller than albumin – it cannot diffuse through pore)
Term
what are plasmalemmal vesicles?
Definition
these do not have much function in terms of transport (quantity) but possibly form vesicular channels
Term
can capillaries in beds of different organs have different structures?
Definition
yes, for example, the capillaries for the glomerulus have lots of gaps - to the point where they is referred to as a "fenestrated capillaries" structured so b/c their function is set up for filtering blood
Term
how can capillaries resist significant pressure?
Definition
the law of laplace states that as radius drops, wall tension drops (T=Pr)
Term
what determines capillary pressure?
Definition
the volume of blood and the compliance of the capillary
Term
is compliance an important determinant of capillary pressure?
Definition
while it is a determinant, capillaries are relatively stiff, so compliance does not play a large role in determinin pressure
Term
what is the major determinant of capillary pressure?
Definition
capillary volume is determined by inflow (influenced by arterial pressure and precapillary resistance) vs outflow (influenced by venous pressure and postcapillary resistance). the resistance of venous structures is approximately 1/4th that of the arterial structures and thus even small **changes in venous pressure affect capillary pressure more than a comparable change in arterial pressure
Term
what are the factors that determine net filtration pressure in the capillary?
Definition
capillary hydrostatic pressure (Pc - pushes fluid out of capillary and into interstitium), interstitial fluid pressure (Pif - driving fluid back into capillary), plasma colloid pressure (PIp - absorbing fluid from interstium), and interstitial fluid colloid osmotic pressure (PIif - pulls fluid out of capillary)
Term
what is starling's law of the capillary?
Definition
Pc-Pif-PIp+PIif = NFP (net filtration pressure, which is usually slightly positive, resulting in filtration out of the capillaries). whatever pushes things out of the capillary has a (+) sign and whatever takes fluid back into the capillary has a (–) sign
Term
what is Kf? how does this value affect NFP?
Definition
Kf is the capillary filtration coefficient for a certain bed which expresses the # and size of pores as well as the # of capillaries (measure of capacity of capillary membranes to filter water for a given NFP). filtration is then = Kf x NFP
Term
does net hydrostatic pressure differ depending on where the capillary is?
Definition
yes, glomerular capillaries' net filtration is 10 mm Hg while in the peritubular capillaries reabsorbtion is 10 mm Hg. in general, mesenteric capillaries absorb and net filtration only occurs in a few places such as the kidneys and glands
Term
what determines the capillary filtration equilibrium point, and how different capillaries fall on either side of it?
Definition
capillary colloid osmotic pressure generally remains the same, but in the arterial end of capillaries, capillary hydrostatic pressure is high (favoring net filtration) which decreases as the capillaries become venous, dropping below capillary colloid osmotic pressure (favoring net absorption). the point where capillary hydrostatic pressure and capillary colloid osmotic pressure meet is the capillary filtration-pressure equilibrium point
Term
how do plasma proteins affect colloid osmotic pressure?
Definition
about 80% of total plasma colloid osmotic pressure results from albumin blood fraction, 20% from globulins, and almost none from fibrinogen
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