Microvasculature II

Question 1

Capillaries are for exchange of materials and the primary site of ________. They are
made up of:

Answer 1

gas exchange; Endothelial cell, basal lamina, an occasional pericyte (mesenchymal,
smooth muscle-like cell; vimentin positive)

Question 2

What is the density of the capillary network related to?

Answer 2

Specific metabolic needs of the tissue

Question 3

Which tissues have high metabolic needs?

Answer 3

Brain, cardiac and skeletal muscle, liver, kidney, lung

Question 4

Which tissues have low metabolic needs?

Answer 4

Connective tissue, smooth muscle

Question 5

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?

Answer 5

Aorta speed – transport. Capillary speed - exchange

Question 6

What are the four forces operating on the capillaries?

Answer 6

Hydrostatic, osmotic, diffusion gradients, directed transcytosis

Question 7

Describe the hydrostatic force on capillaries

Answer 7

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

Question 8

Describe the osmotic force on capillaries

Answer 8

drives fluid back into vessel, metabolic byproducts (on venous side of capillary bed)
*What is not taken back is handled by lymphatic drainage

Question 9

What are the four types of capillaries?

Answer 9

Continuous capillaries (no fenestrations in wall); fenestrated capillaries (large fenestrae
in wall); fenestrated capillaries with no diaphragms; discontinuous sinusoidal capillaries

Question 10

Where would you find continuous capillaries? What kind of transport is involved?

Answer 10

found in muscle, connective tissue, exocrine glands, nervous tissue - usually has
pinocytotic vesicles on surfaces of endothelial cell - active transport

Question 11

Where would you find fenestrated capillaries with large fenestrae in wall? What is the function?

Answer 11

with diaphragms narrower that cell membrane - basal lamina is continuous - found in
kidney, intestine, endocrine glands - rapid exchange needs

Question 12

Where might you find fenestrated capillaries with no diaphragms?

Answer 12

renal glomerulus - thick and continuous basal lamina - only thing that separates blood
from tissue fluid

Question 13

Describe discontinuous sinusoidal capillaries and where you would find them

Answer 13

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

Question 14

Compare the postcapillary venules in terms of pericytes and fluid. What forces are
involved?

Answer 14

Postcapillary venules - More percityes, but not a continuous layer. Will contain more
fluid than capillaries. Forces: Osmotic

Question 15

What is the key role of the poscapillary venules?

Answer 15

Key role in blood-interstitial fluid exchange/balance. Exchange of materials (fluid
exchange both ways)

Question 16

Describe the venule

Answer 16

Site of fluid movements. Very senstitive to Temp. and inflammatory conditions. Do not
have much hydrostatic pressure – structure reflects this

Question 17

Postcapillary venules are sensitive to ____________ - induce _____ into tissue space

Answer 17

sensitive to histamine, serotonin, bradykinins; leakage

Question 18

What is there to the collecting venules? What about the muscular venules?

Answer 18

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

Question 19

Which vessel will have a larger lumen, thinner wall, be irregular shaped, and have
layers less demarcated, arteries or veins?

Answer 19

Veins

Question 20

What is important about veins? How do veins move blood back to the heart without
much hydrostatic pressure?

Answer 20

Capacitance. Valves and adventitia are key to their function. (and longitudinal smooth
muscle rhythmic contractions in large veins and some medium veins)

Question 21

Distinguish small, medium, and large veins

Answer 21

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)

Question 22

How do veins return blood?

Answer 22

Rhythmic contractions = move blood back, valves stop backflow

Question 23

What are arteriovenous anastomoses? Give an example

Answer 23

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.

Question 24

What are characteristics of the pulmonary circulatory system?

Answer 24

Low pressure system, elastic arteries – elastic fibers are more irregular in media, elastic fibers are more longitudinal – relates to breathing

Question 25

Give two examples of portal vessels systems

Answer 25

Hepatic portal system – connects capillaries of intestine directly to capillaries of liver.
Portal vessels in pituitary – connects hypothalamus to the anterior pituitary

Question 26

Where does the lymphatic circulatory system drain to? Where does it intersect the
venous system?

Answer 26

Drains to thoracic duct & left lymphatic duct - intersects venous system at junction of jugular and subclavian veins

Question 27

True or false. Lymph has valve-like flaps.

Answer 27

True

Question 28

What is the basic problem of atherosclerosis? List 7 contributing factors.

Answer 28

Basic Problem: Damage to vessel wall and predictable repair responses

Contributing Factors:

• Hemodynamic stress (high BP) - Injury - Ischemia - Inflammation
• Excess LDL - Drugs - Hormones