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Lymphatic
System
Chapter 12
Introduction

Components
Lymph is the fluid
Vessels – lymphatics
Structures & organs
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Functions
Return tissue fluid to the bloodstream
Transport fats from the digestive tract to the
bloodstream
Surveillance & defense
The Lymphatic System
Lymphatics
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Originate as lymph capillaries
Capillaries unite to form larger vessels
Resemble veins in structure
Connect to lymph nodes at various intervals
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Lymphatics ultimately deliver lymph into 2
main channels
Empty into large veins just before they join the
superior vena cava
Lymph Capillaries
Lymphatic Vessels
Main Channels of Lymphatics
Major Lymphatic Vessels of the
Trunk
Lymph Tissue
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3 types
Diffuse lymphatic tissue
Lymphatic nodules
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Some are found singly
Some are found in clusters in specific areas
Eg. Tonsils; appendix
Lymphatic organs
Lymph Nodules
Lymph Nodes
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Oval structures located along lymphatics
Enclosed by a fibrous capsule
Divided into compartments
Sinuses
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Produce lymphocytes
Lymph enters nodes through afferent
lymphatics, flows through sinuses, exits
through efferent lymphatic
Lymph Node
Tonsils
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Multiple groups of large lymphatic nodules
Location – mucous membrane of the oral and
pharyngeal cavities
Palatine tonsils
Posterior-lateral walls of the oropharynx
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Pharyngeal tonsil
Posterior wall of nasopharynx
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Lingual tonsils
Base of tongue
Tonsils
Spleen
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Largest lymphatic organ
Located between the stomach & diaphragm
Structure is similar to a node
Capsule present
But no afferent vessels or sinuses
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Contains
Lymphatic tissue
Red blood cells
Lymphocytes (plasma cells)
Other leucocytes
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Functions
Filters blood
Stores blood
Spleen
Thymus Gland
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Location – behind the sternum
The capsule divides it into 2 lobes
Development
Infant – conspicuous
Puberty – maximum size
Maturity – decreases in size
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Function
Differentiation and maturation of T cells
Thymus Gland
Function of the Lymphatic
System
Defense against harmful organisms
and chemicals
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Nonspecific resistance
Inherited
Wide variety of body reactions against a
wide range of pathogens
Specific resistance
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Resistance to a specific disease-causing
microorganism
Nonspecific Resistance
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Skin
1st line of defense
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Mechanical and chemical factors that fight disease
Tears
Saliva
Flow of urine
Gastric juice
Nonspecific Resistance
(cont’d)
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Interferon (IFN)
Produced by body cells infected with viruses
Then released by the infected cells
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Inhibits viral replication in neighboring cells
Decreases disease-producing power of many
viruses
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Phagocytosis
Inflammation
Fever
Specific Resistance = Immunity
Involves the production of a specific cell or
molecule (antibody) to destroy a specific
disease-causing organism or its toxin
(antigen).
Innate Immunity
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Inborn immunity
Acquired Immunity
Immunity acquired during organisms’ lifetime
Characteristics of the Immune
Response
Specificity
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Involves the production of a specific cell or antibody
to destroy a particular antigen
Memory
Acquired ability to detect and eliminate foreign
substances
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Self vs. non-self recognition
MHC
Involves antibody-mediated and cell-mediated
immunity
Lymphocytes Initiate the
Immune Response
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Types of lymphocytes
T cells
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80% of circulating lymphocytes
B cells
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10 – 15% of circulating lymphocytes
NK cells
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5 – 10% of circulating lymphocytes
Derivation and Distribution of
Lymphocytes
Distribution and Life Span of
Lymphocytes
Ratio of B cells to T cells varies
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Depends on the tissue or organ considered
Lymphocytes continually move throughout the
body (wanderers)
Lymphocytes have relatively long life
spans
Lymphocytes and the Immune
Response
2 components
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Cell-mediated immunity
Direct attack by T cells
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Virus & bacterial infected host cells, fungi, parasites,
transplanted tissues, tumors, etc.
Antibody-mediated immunity
Attack by circulating antibodies
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Released by plasma cells derived from activated B
lymphocytes
Lymphocytes and the
Immune Response
What is an antigen?
Antigen = “antibody generating” molecule

any chemical substance that, when introduced into
the body, causes the body to produce specific
antibodies that can react with the antigen
Properties of antigens:
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Foreign proteins or polysaccharides
Examples:
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Cell membranes, flagella, viruses, toxins, enzymes,
pollen, transplanted tissues & organs, markers on red
blood cells
Cell-mediated Immunity
Characteristics of the Cell
Mediated Immune System
Upon interaction with specific antigens, specific
T cells produce cytokines
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Proteins that activate both B & T cells
Do not secrete antibodies
Found in lymphoid tissue (nodes, blood, spleen)
Act primarily on intracellular parasites (viruses,
some bacteria), fungi & worms, cancer cells &
transplanted tissues
T Cells and Immunity
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1000s of different types of T cells
When an antigen enters the body, only the particular
T cell programmed to react with the antigen becomes
activated
Macrophages phagocytize the antigen
Macrophages present it to the T cell
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T cells increase in size, divide, differentiate
Cytotoxic T cells
Helper T cells
Memory T cells
Delayed hypersensitivity T cells
Suppressor T cells
Duality of the Immune System
Cytotoxic T Cells (TC)
Migrate to the site of invasion
Attach to the invading cell
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Secrete substances that lyse the infected cell.
Secrete interferon
A TC Cell Lyses an Infected Cell
Helper T Cells (TH Cells)
Assist in the regulation and coordination of he
immune response
Steps of regulation
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1. Processing
Macrophage phagocytizes antigen, presents it on its surface
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2. Recognition
Appropriate TH cell binds to the macrophage
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3. Stimulation
Macrophage stimulates TH cell to form a clone of TH cells
Cloned cells produce cytokines
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Stimulate B cells and TC cells
4. Response
TC cells kill infected cells, B cells produce antibodies
The Role of Helper T Cells as
Mediators of Immune Responses
Memory T Cells
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Recognize original invading
organism if the pathogen invades
later
Swifter reaction than during the 1st
invasion
Pathogen is usually destroyed before
any symptoms appear
Other T Cells
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Delayed hypersensitivity T cells (TD)
Key factor in allergy responses and transplant
tissue rejection
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Suppressor T cells (TS)
Turn off the immune response
Additional Cell Components
Macrophages
 Present antigen to TH cells, eliminate viral &
bacterial infected cells, attack cancer cells,
activated by antigen and cytokines from TH
cells
Natural Killer Cells
 Attack and lyse foreign cells, normal cells
infected with viruses, and cancer cells
 Non-specific in action
Antibody-Mediated
Immunity
B Cells
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1000s of different kinds of B cells
Each type responds to a specific antigen
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When an antigen enters the blood
B cells are activated
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Become plasma cells
Circulate in blood and lymph to reach site of
invasion
B cells become memory B cells
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Respond more rapidly and forcefully should a
2nd invasion occur
What does an antigen do?
Antigen with its antigenic determinant stimulates
the formation of specific antibodies
The antigenic determinant, a portion of the
antigen, reacts with an antibody to form an
antigen-antibody complex
The formation of the antigen-antibody complex
ultimately leads to inactivation and removal of
the antigen
Antigenic Determinants on an
Antigen
What is an antibody?
Large Proteins
Basic subunit has minimum of two binding sites
at which it combines with antigens
Also known as “immunoglobulins”
Antibody Configuration
2 Methods of Antibody
Production
T cell independent production
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B cells differentiate without the interaction of
TH cells
T cell dependent production
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B cells differentiate with the interaction of TH
cells
T cell Independent Antigens
T cell Dependent Antigens &
Antibody Production
Outcome of Antibody Production
by B cells
Disorders of the Immune
System
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Allergy
Person is overly reactive to an antigen
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Autoimmune diseases
Body has difficulty in discriminating between its own antigens
and foreign antigens
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Severe Combined Immunodeficiency (SCID)
Both T cells and B cells are absent or inactive
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Acquired Immune Deficiency Syndrome (AIDS)
Human immunodeficiency virus (HIV)
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Primarily attacks helper T cells