Transcript The exchange of substances between the blood and the

Lymphatic System
The exchange of substances between the blood
and the interstitial fluid that bathes the cells takes
place across the thin walls of the capillaries.
As blood proceeds along the capillary:
1.
2.
3.
Blood pressure drops
The capillary becomes hypertonic compared to the
surrounding tissue fluids
The resulting osmotic gradient pulls water into the capillary by
osmosis near the venule end.
• 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.
• Fluid enters this system by diffusing into tiny lymph
capillaries intermingled among capillaries of the
cardiovascular 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.
• Lymph vessels, like
veins, have valves that
prevent the backflow of
fluid toward the
capillaries.
• Rhythmic contraction of
the vessel walls help
draw fluid into lymphatic
capillaries.
• Also like veins, lymph
vessels depend mainly on
the movement of skeletal
muscle to squeeze fluid
toward the heart.
• Along a lymph vessels are organs called lymph
nodes.
• Inside a lymph node is a honeycomb of
connective tissue with spaces filled with
leukocytes (WBC) called lymphocytes and
macrophages
• Lymphocytes and macrophages are
specialized for attacking viruses and bacteria.
• When the body is fighting an infection, these
cells multiply, and the lymph nodes become
swollen.
• In addition to
defending against
infection and
maintaining the
volume and protein
concentration of the
blood, the lymphatic
system transports fats
from the digestive
tract to the circulatory
system.
Blood
Figure 42.14 The composition of mammalian blood
0%
99%
<1%
<1%
Figure 42.14x Blood smear
erythrocyte
platelet
leukocytes
Figure 42.15 Differentiation of blood cells
Macrophages
Erythrocytes
• Biconcave in shape due to absence of
nucleus
• Absence of nucleus  lifespan of 120
days
• Dead erythrocytes recycled by spleen and
liver into bilirubin  bile
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
Regulation of Erythrocytes
4) + High blood O2
5) - erythropoietin
3) + erythrocytes
1) + Low blood O2
2) + erythropoietin
Blood Clotting
• Platelets initiate
clotting at site of tear
in blood vessel wall
• Fibrin is produced to
seal any leaks in the
blood clot
• Platelets + Fibrin +
Pus = Scab
Figure 42.16x Blood clot
Mechanism of Blood Clotting