9-circulatory systems in animals part 2
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Lymphatic System
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The exchange of substances between the blood
and the interstitial fluid that bathes the cells takes
place across the thin walls of the capillaries.
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As blood proceeds along the capillary:1. Blood pressure drops
2. The capillary becomes hypertonic compared to thesurrounding tissue fluids
3. The resulting osmotic gradient pulls water into the capillary byosmosis near the venule end.
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About 85% of the fluid that leaves the
blood at the arterial end of the capillary
bed re-enters from the interstitial fluid at
the venous end.
The remaining 15% is eventually returned
to the blood by the vessels of the
lymphatic system.
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Fluid enters this system by diffusing into tiny lymphcapillaries intermingled among capillaries of thecardiovascular system.
Once inside the lymphatic system, the fluid is called
lymph, with a composition similar to the interstitial fluid. Eventually the lymphatic system drains into the
circulatory system near the subclavian veins.
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Lymph vessels, like
veins, have valves thatprevent the backflow offluid toward thecapillaries.
Rhythmic contraction ofthe vessel walls helpdraw fluid into lymphaticcapillaries.
Also like veins, lymph
vessels depend mainly onthe movement of skeletalmuscle to squeeze fluidtoward the heart.
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Along a lymph vessels are organs called lymph
nodes. Inside a lymph node is a honeycomb of
connective tissue with spaces filled withleukocytes (WBC) called lymphocytes and
macrophages Lymphocytes and macrophages are
specialized for attacking viruses and bacteria.
When the body is fighting an infection, thesecells multiply, and the lymph nodes becomeswollen.
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In addition to
defending against
infection and
maintaining thevolume and protein
concentration of the
blood, the lymphatic
system transports fatsfrom the digestive
tract to the circulatory
system.
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Blood
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Figure 42.14 The composition of mammalian blood
99%
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Figure 42.14x Blood smear
erythrocyte
platelet
leukocytes
Fi 42 1 Diff i i f bl d ll
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Figure 42.15 Differentiation of blood cells
Macrophages
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Erythrocytes
Biconcave in shape due to absence of
nucleus
Absence of nucleuslifespan of 120
days
Dead erythrocytes recycled by spleen and
liver into bilirubinbile
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Erythrocytes
Hemoglobin is the protein
attached to the
erythrocyte
Hemoglobin has 4
polypeptide chains
(quaternary structure)
Each polypeptide chain
has a heme (iron) group
that binds O2
Therefore one erythrocyte
carries 8 oxygen atoms
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Regulation of Erythrocytes
1) + Low blood O2
2) + erythropoietin
3) + erythrocytes
4) + High blood O2
5) - erythropoietin
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Blood Clotting
Platelets initiate
clotting at site of tear
in blood vessel wall
Fibrin is produced toseal any leaks in the
blood clot
Platelets + Fibrin +
Pus = Scab
Fig re 42 16 Blood clot
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Figure 42.16x Blood clot
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Mechanism of Blood Clotting