Mutafova Microcirculation Flashcards
At what level does the blood brain barrier occur?
At the capillary level!
What is the rough diameter of the capillaries & the velocity of blood flowing through there & the amount of time blood spends there?
Very small diameter.
Very slow velocity. B/c large cross sectional area.
Slow velocity allows blood to spend more time there, but still not very much time at all (1-3 seconds). Amazing that exchange can happen!
Although the velocity of blood flow isn’t constant across circulation, what is constant?
The volume of blood flow through each portion of circulation per unit time.
Do capillaries have smooth muscle? Arterioles? Venules Veins? Metarterioles?
Arterioles--yes metarterioles--yes capillaries--no small venules--yes veins--yes
What is the precapillary sphincter?
A strong muscle that restricts blood flow into the capillaries. It is regulated.
What are the 2 main mechanisms of regulating blood flow thru the capillaries?
Constriction of the arterioles & precapillary sphincters.
What is the direction of blood flow thru capillaries? Is there a pressure difference? Diameter difference?
Arterioles–>Metarterioles–>Precapillary Sphincter–>Capillaries–>Collecting Venules–>Small Venules–>Veins
There is a higher pressure in the arterial side of capillaries & a smaller diameter on this size. The difference is important for blood flow.
How many blood cells can pass thru a capillary at a time? Why is this important?
1 at a time.
This way there is no competition b/w blood cells to exchange nutrients & gases.
Each cells gets to do its thing & then leave.
What is the composition of true capillaries?
A single layer of endothelial cells w/ a basement membrane on the outside (not the luminal side).
How do water soluble molecules pass thru the capillaries? How do lipid soluble molecules pass thru? How do large molecules pass thru? Any other mechanisms?
Water soluble molecules pass thru the intercellular (b/w cells) clefts in the endothelial cells.
Lipid soluble molecules pass thru by diffusion.
Large hydrophilic molecules (macromolecules) can pass thru w/ pinocytosis or vesicle formation.
Some molecules like ions pass thru w/ active transport, a pump.
What are the 3 types of capillaries in systemic circulation & where are they found?
Continuous Capillary: most common form. very small, small holes. Have intercellular jcns.
Fenestrated Capillary: have fenestrae (larger holes that allow for movement of substances).
Found in kidney glomeruli, exocrine glands, Small intestine
Sinusoidal Capillary/Discontinuous: Have large fenestrations & gap jcns (allow movement of proteins). Found in the liver, bone marrow, & spleen.
What is the most common pathway to get molecules across a capillary?
Diffusion. Lipid soluble molecules down their conc’n gradient. Explains why O2 & CO2 can move as they do.
How is glucose transported in most systemic capillaries?
Diffusion thru the endothelial pores or clefts. In some systems (like brain) active transport.
How are steroid hormones transported across capillaries?
By diffusion across the plasma membrane
How are the meds for anesthesia transported across capillaries?
By diffusion across the plasma membrane
How are amino acids transported across capillaries?
By diffusion thru endothelial pores or clefts.
What is hydrostatic pressure? How does it relate to capillaries?
the pressure of the weight of the blood. Equivalent to blood pressure.
Hydrostatic pressure is always greater in the lumen of the capillary than in the interstitial fluid. This allows for movement of substances out of the endothelial pores.
