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Chapter 15
The Lymphatic System
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Introduction
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Transports lymph through lymphatics
Lymphatics: lymph capillaries and vessels
Controls body fluid
Destroys harmful microorganisms
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Introduction
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The Functions of the System
and the Structure and
Functions of the Lymphatic
Vessels
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Introduction
• Drain interstitial fluid from tissue spaces
– Prevent edema
• Transport digested fat to blood
– Lacteals: special lymphatics in small intestine
– Chyle: milky lymph in lacteals
• Develop immunities
• Produce lymphocytes
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Lymphatic Vessels
• Lymph capillaries: blind-end tubes
• Lymph capillaries are located between
cells
• Lymph capillaries unite to form lymphatics
• Lymphatics converge into two main
channels
– Thoracic duct and right lymphatic duct
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Lymphatic Vessels (cont’d.)
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Lymph Nodes
• Found along lengths of lymphatics
• Efferent: exit lymph node at the hilum
• Afferent: enter lymph node at various
locations
• Trabeculae: divide the node into
compartments
• Germinal centers of compartments
produce lymphocytes
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Lymph Nodes
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Lymph Nodes
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Lymph Circulation
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Lymph Circulation (cont’d.)
• Interstitial fluid: plasma in interstitial
spaces
• Lymph: interstitial fluid in lymph capillaries
– Passes into lymphatics
• Lymphatics join to form lymph trunks
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Lymph Circulation (cont’d.)
• Lymph circulation maintained by
– Normal skeletal muscle contractions
• Compresses lymph vessels and forces lymph in
one direction
– Respiratory or breathing movements
– Smooth muscle in lymphatic vessels
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Lymph Circulation (cont’d.)
• Lymph trunks
– Lumbar: drains lower extremities and pelvis
– Intestinal: drains abdominal region
– Bronchomediastinal and intercostal: drain
thorax
– Subclavian: drains upper extremities
– Jugular: drains head and neck
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Lymph Circulation (cont’d.)
• Individual trunks drain into two main trunks
– Thoracic duct: drains into the left subclavian
vein
– Right lymphatic duct: drains into the right
subclavian vein
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Lymph Circulation (cont’d.)
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The Organs of the Lymphatic
System
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The Organs of the Lymphatic
System (cont’d.)
• Tonsils
– Palatine, pharyngeal, and lingual
– Protect the nose and oral cavity
• Thymus: lymphocyte production and
maturation
• Peyer’s patches: found in walls of small
intestine
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The Organs of the Lymphatic
System (cont’d.)
• Spleen
– Largest mass of lymphatic tissue
– Phagocytizes worn-out RBCs and platelets
• Recycles hemoglobin
– Produces lymphocytes and plasma cells
– Stores blood for release during hemorrhage
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The Organs of the Lymphatic
System (cont’d.)
• External view
of the Spleen
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Immunity
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Immunity (cont’d.)
• Ability of body to resist
– Infection from pathogens
– Damage from foreign substances and harmful
chemicals
• Humoral immunity
– B lymphocytes: produce antibodies
• Fight circulating bacteria and viral infections
• Become plasma cells when they enter tissues
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Immunity (cont’d.)
• Cellular immunity
– T lymphocytes
• Come from thymus glands
• Fight intracellular viruses, fungi, parasites, cancer
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Antigens and Antibodies
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Antigens and Antibodies (cont’d.)
• Antigen: foreign protein in our body
• B lymphocytes
– Produce antibodies in response to antigens
– Antibodies bind to specific antigen
– Antigens precipitate
– Phagocytic WBCs eat the antigens
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Antigens and Antibodies (cont’d.)
• Antibody morphology
– Four amino acid chains linked by disulfide
bonds
• Heavy and light chains
– Y-shaped molecule
– Binding sites at tips of Y
– Stem of the Y is always constant
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Antigens and Antibodies (cont’d.)
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Antigens and Antibodies (cont’d.)
• Antibody types
– IgG: attacks viruses, bacteria, and toxins;
activates complement
– IgA: found in exocrine gland secretions
– IgM: response to bacteria or food antigens
– IgD: found on surface of B lymphocytes
– IgE: associated with allergic reactions
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Antigens and Antibodies (cont’d.)
• Active immunity: B cells contact antigen
and produce antibodies
– Natural active: exposure to infection
– Artificial active: vaccine
• Passive immunity
– Natural passive: maternal antibodies to fetus
– Artificial passive: gamma globulin
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Cells of the Immune
Response and Other
Defenses
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Cells of the Immune Response and
Other Defenses (cont’d.)
• B cells: antigen
– Antibody binding
• Plasma cells: replicated B cells
• Helper T cells: stimulate production of
– Killer T cells
– More B cells
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Cells of the Immune Response and
Other Defenses (cont’d.)
• Killer T cells:
– Attack virus-invaded body cells
– Attack cancer cells
– Reject body grafts
• Memory cells: descendents of activated T
and B cells
• Suppressor T cells: slow down activities of
B and T cells
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Cells of the Immune Response and
Other Defenses (cont’d.)
• Macrophages
– Engulf and digest antigen
– Present them to T cell for recognition
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Cells of the Immune Response and
Other Defenses (cont’d.)
• Lymphokines: chemicals released by
sensitized T cells
• Monokines: chemicals released by
activated macrophages
• Skin: mechanical barrier
– Acid mantle, sebum
• Lysozyme: (tears and saliva) attacks
bacteria
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Cells of the Immune Response and
Other Defenses (cont’d.)
• Mucous membranes: trap microorganisms
and debris
• Hydrochloric acid: (stomach) destroys
microorganisms
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Summary
• Discussed the functions of the immune
system
• Described lymph and its flow through the
body
• Discussed the functions of the spleen and
tonsils
• Described the different types of immunity
• Discussed the immune response
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