Ø Capillary (微血管) CE-2005-I-B-Q8a
n connect the
arterioles (小動脈) to the venules (小靜脈).
n form (13) capillary beds (微血管床)
in the body
tissue to allow exchange of materials
between
blood and body
cells.
n Structure of a
capillary:
(14) one-cell
(15) differentially
n
adaptive features of capillary to
facilitate (16) exchange of
materials:
Feature
|
Description
|
Branched into an
extensive network
|
increase
the surface area for efficient exchange of
materials
|
Large
cross-section area
|
Reduce
the blood flow rate, thus increasing the time of
material exchange between the blood and the body cells
|
Thin wall (only (17) one-cell thick)
|
reduce the (18) diffusion distance across the blood vessels
|
Ø The change in blood pressure along different blood
vessels: CE-2008-IB-Q9b
Blood vessel
|
Blood pressure
|
Arteries and arterioles
|
n (19) High due to the pumping action of the heart
n Changes (20) periodically as the heart
contracts and relaxes
|
Capillaries
|
n Drops significantly because the small diameter of the capillaries
offers a
high (21) resistance to blood flow
|
Veins and venules
|
n Much lower because the blood has overcome great resistance of the
blood vessel walls after travelling a long distance
|
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