8.6 Exchange of
materials between
blood and body
cells (Book 1B, p. 8-25)
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A
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How are materials
exchanged between blood and body cells?
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(Book 1B, p. 8-25)
Ø All body cells
are bathed in (1) tissue fluid (組織液).
Ø Exchange of materials:
n takes place at
the (2) capillaries
n useful materials
in the blood diffuse into the (3) tissue fluid / interstitial space and then into the
body cells
n Waste products
from body cells diffuse in the opposite direction.
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Body cells
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«
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Capillary wall
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¬ (Diffusion) ®
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Tissue fluid
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«
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Wastes
(e.g. CO2)
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Ø Adaptation of
capillaries for exchange of materials:
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Feature
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Adaptation
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Thin wall (one-cell
thick walls)
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Provides a (4) short distance for diffusion
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Numerous
branches
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Provide a large (5) surface area for diffusion
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Large total (6)
cross-sectional area
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(7) Slow blood flow
allows more time for exchange of
materials
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B
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How is tissue fluid
formed? (Book 1B, p. 8-26)
AL-2005-II-B-Q5b
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Ø At the arteriole end, the (8) pressure of blood in the capillaries is (9) higher /
lower than that of the fluid surrounding the body cells. This forces some components of the plasma
(e.g. water, minerals, sugars, lipids and hormones) out of the capillary walls.
Ø The walls of
capillaries are (9) differentially permeable which do not allow substances
of too large size to pass through, e.g.:
n red blood cells
n (10) blood platelets
n plasma (11) proteins
Ø (12) White blood
cells / Phagocytes can squeeze through the capillary walls and enter
the tissue fluid.
Ø The composition of tissue fluid is similar to (13) blood, except for the absence of red blood cells, blood platelets and plasma proteins.
Ø At the venule end, the (14) water potential of the blood is (15) higher than that of the
tissue fluid as plasma proteins remain in the blood. Water in the tissue fluid
is drawn
into the capillaries by (16) osmosis.
Ø A small amount of
tissue fluid drains into the (14) lymph capillaries (淋巴微管), and will return
to the circulatory system ultimately.
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C
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What is the importance
of tissue fluid?
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(Book 1B, p. 8-27)
Ø Provides a
relatively (15) constant environment for body cells
Ø Serves as an important
link for the (17) exchange of materials between capillaries
and body cells
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