Microvasculature II Flashcards
Capillaries are for exchange of materials and the primary site of ________. They are
made up of:
gas exchange; Endothelial cell, basal lamina, an occasional pericyte (mesenchymal,
smooth muscle-like cell; vimentin positive)
What is the density of the capillary network related to?
Specific metabolic needs of the tissue
Which tissues have high metabolic needs?
Brain, cardiac and skeletal muscle, liver, kidney, lung
Which tissues have low metabolic needs?
Connective tissue, smooth muscle
The velocity of the blood high in the aorta (320 mm/s) and low in capillaries (0.3 mm/s).
What is the function of each of these?
Aorta speed – transport. Capillary speed - exchange
What are the four forces operating on the capillaries?
Hydrostatic, osmotic, diffusion gradients, directed transcytosis
Describe the hydrostatic force on capillaries
drives fluid out of capillary, nutrients provided to tissue on arterial side of the capillary
bed - water and other hydrophilic molecules less that 1.5 nm or 10 kDa in size can diffuse
through intercellular tight junctions and gaps when leaky
Describe the osmotic force on capillaries
drives fluid back into vessel, metabolic byproducts (on venous side of capillary bed)
*What is not taken back is handled by lymphatic drainage
What are the four types of capillaries?
Continuous capillaries (no fenestrations in wall); fenestrated capillaries (large fenestrae in wall); fenestrated capillaries with no diaphragms; discontinuous sinusoidal capillaries
Where would you find continuous capillaries? What kind of transport is involved?
found in muscle, connective tissue, exocrine glands, nervous tissue - usually has
pinocytotic vesicles on surfaces of endothelial cell - active transport
Where would you find fenestrated capillaries with large fenestrae in wall? What is the function?
with diaphragms narrower that cell membrane - basal lamina is continuous - found in
kidney, intestine, endocrine glands - rapid exchange needs
Where might you find fenestrated capillaries with no diaphragms?
renal glomerulus - thick and continuous basal lamina - only thing that separates blood
from tissue fluid
Describe discontinuous sinusoidal capillaries and where you would find them
large diameter - tortuous vessels - discontinuous endothelial layer and basal lamina -
multiple fenestrations - macrophages outside of vessel wall - liver, spleen, bone marrow -
major exchange sites - cells and fluids
Compare the postcapillary venules in terms of pericytes and fluid. What forces are
involved?
Postcapillary venules - More percityes, but not a continuous layer. Will contain more
fluid than capillaries. Forces: Osmotic
What is the key role of the poscapillary venules?
Key role in blood-interstitial fluid exchange/balance. Exchange of materials (fluid
exchange both ways)
Describe the venule
Site of fluid movements. Very senstitive to Temp. and inflammatory conditions. Do not
have much hydrostatic pressure – structure reflects this
Postcapillary venules are sensitive to ____________ - induce _____ into tissue space
sensitive to histamine, serotonin, bradykinins; leakage
What is there to the collecting venules? What about the muscular venules?
Collecting venules: pericyte layer is now continuous. Start seeing some collagen fibers
and adventitia formation. Muscular venules – smooth muscle replaces pericytes in tunica
media – 1-2 layers thick. Fibrous adventitia can usually be seen
Which vessel will have a larger lumen, thinner wall, be irregular shaped, and have
layers less demarcated, arteries or veins?
Veins
What is important about veins? How do veins move blood back to the heart without
much hydrostatic pressure?
Capacitance. Valves and adventitia are key to their function. (and longitudinal smooth
muscle rhythmic contractions in large veins and some medium veins)
Distinguish small, medium, and large veins
Small: continuous with muscular venules (~1 mm diameter). Medium: have better
developed adventitia – longitudinal orientation of components (1-10 mm diameter). Large:
more fibers in subendothelial space – media has some longitudinal oriented SMC + some
elastic fibers – adventitia has some longitudinal SMC, is well developed (1-4 cm diameter)
How do veins return blood?
Rhythmic contractions = move blood back, valves stop backflow
What are arteriovenous anastomoses? Give an example
Vessels that bypass the capillary bed – arteriole to venule. Thermoregulation of skin an
example. Another note: arteriole-metarteriole the muscle will contract to shunt the blood to
capillaries, relax to open shunt.
What are characteristics of the pulmonary circulatory system?
Low pressure system, elastic arteries – elastic fibers are more irregular in media, elastic fibers are more longitudinal – relates to breathing
