Download Chapter Twenty Four

Lymphatic System
Functions of the Lymphatic System
1. Return interstitial fluid to bloodstream
2. Transport lipids and lipid-soluble vitamins in the
bloodstream
3. Production and maturation of lymphocytes
4. Generates an immune response against antigens
in interstitial fluid
Lymphatic System
Lymph
Lymph is fluid in lymphatic vessels
Comprised of:
• Interstitial fluid
• Solutes
• Foreign materials
Lymphatic Capillaries
• Closed-ended tubes; among blood capillary
beds
• GI tract contains specialized lymph capillaries
called lacteals
– collect lipids and lipid-soluble vitamins
Lymphatic Vessels
• Lymphatic capillaries merge
to form lymphatic vessels
– Resemble venules
• Possess valves similar to
veins
• Afferent lymphatic vessels
 into lymph node
• Efferent lymphatic vessels
 away from lymph node
• Lymphatic vessels merge 
lymphatic trunks
Lymphatic Trunks
Lymphatic Ducts
• Lymphatic trunks 
Lymphatic ducts
• Right lymphatic duct – Returns lymph from right side
of head/neck, upper limb and
thorax
• Thoracic duct - largest
lymphatic vessel
– collects lymph from rest of
body
Lymphatic Cells
•
Macrophages
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Nurse cells
–
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Secrete hormones in thymus
Dendritic cells
–
–
•
Monocytes that have migrated
Phagocytize foreign substances
In lymph nodules
Antigen-presenting cells
Lymphocytes
Types of Lymphocytes
•
Three types of lymphocytes:
1. T-lymphocytes (T-cells)
2. B-lymphocytes (B-cells)
3. NK cells
T-Lymphocytes
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•
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70-85% of lymphocytes
Can recognize a particular antigen
Main types:
 Helper T-lymphocytes
 Cytotoxic T-lymphocytes
 Memory T-lymphocytes
Helper T-Lymphocytes
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•
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Also called CD4 or T4 cells
Many types, each responds to a different
antigen
T4 cells initiate and oversee the immune
response
1. Present antigen to other lymphocytes
2. Secrete cytokines - hormones that activate other
lymphatic cells
• HIV infects these cells
– Shuts down immune response
Cytotoxic T-Lymphocytes
• Also called CD8 or T8 cells
• Come in direct contact w/infected or foreign
cells and kill them
• Must be activated by helper T-cell that
presents an antigen to it
Immune Response of T-Lymphocytes
Memory T-Lymphocytes
• Arise from T cells that have encountered
antigen
• Mount faster response than initial exposure
B-Lymphocytes
• 15-30% of body lymphocytes
• Produce immunoglobins (Ig), or antibodies,
to a single antigen
• Become activated when presented with antigen
from helper T- cell
– Undergo division to two cell types:
• Most become plasma cells – produce antibodies
– Live less than a week
• Some become memory B cells
– Live weeks to years
– Confer lifetime immunity
B-Lymphocytes and Their Role in
the Immune Response
NK (Natural Killer) Cells
• Small percentage of all lymphocytes
• Can kill a wide variety of infected cells and
some cancerous cells
Lymphatic Organs
• Tonsils – trap antigens
• Thymus – T cell maturation
• Lymph nodes – filter antigens
from lymph
• Spleen
Spleen
1. Initiates immune response
when antigens found in
blood
2. Reservoir for erythrocytes
and platelets
3. Phagocytizes old, defective
erythrocytes and platelets
4. Phagocytizes bacteria and
other foreign materials