Chapter 14: The Lymphatic

System and Immunity

Functions of The Lymphatic System

• Produce, maintain, and distribute lymphocytes

• Return fluid and solutes to the blood• Distribute hormones, nutrients, and

wastes from tissues to circulatory system

• Helps to protects us against pathogens and disease

Organization of the Lymphatic System

•Lymphatic Vessels•Lymph•Thymus•Spleen•Lymphocytes

4 Parts of the Lymphatic System

1. Lymphatic vessels (lymphatics): – network that carries lymph from

peripheral tissues to the venous system

2. Lymph: – a fluid similar to plasma– does not have plasma proteins

4 Parts of the Lymphatic System

3. Lymphoid tissues and lymphoid organs:

– found throughout the body

4. Lymphocytes, phagocytes, and other immune system cells

Figure 22–3

Lymphatic Vessels and Valves

The Thoracic Duct

• Collects lymph from:• left

bronchiomediastinal trunk

• left subclavian trunk• left jugular trunk

• Empties into left subclavian vein

Collects lymph from:• right jugular trunk• right subclavian

trunk• right

bronchiomediastinal trunk

•Empties into right subclavian vein

The Right Lymphatic Duct

Figure 22–4

Lymphatic Ducts and the Venous System

Lymphoid Tissues

• Connective tissue

• dominated by lymphocytes

Distribution of Lymph Tissues and Nodes

• Lymph nodes• Respiratory tract (tonsils)

– left and right palatine tonsils– pharyngeal tonsil (adenoid)– 2 lingual tonsils

• Along digestive and urinary tracts

Lymph Nodes• A filter:

– purifies lymph before return to venous circulation

• Removes:– debris– pathogens– 99% of antigens

Lymphoid Organs

Thymus • Lymphocytes

divide in the thymus

• Mature T Cells leave the thymus

• Deteriorates after puberty:– diminishing

effectiveness of immune system

Lymphoid OrgansSpleen 1. Removes abnormal

blood cells and other components by phagocytosis

2. Stores iron recycled from RBC’s

3. Initiates activities by B cells and T cells in response to antigens in circulating blood

Lymphocytes• Make up 20–30% of circulating

leukocytes• Lymphocytes are produced:

– in lymphoid tissues (e.g., tonsils)– lymphoid organs (e.g., spleen,

thymus)– and in red bone marrow

• Lymphocytes: – detect problems– travel into site of injury or infection

3 Classes of Circulating

Lymphocytes1. T cells:– thymus-dependent

2. B cells:– bone–marrow derived

3. NK cells:– natural killer cells

T Cells • Make up 80% of circulating

lymphocytes• Produce cell-mediated immunity

3 Main TypesCytotoxic T Cells - Attack cells infected by viruses Helper T Cells - Stimulate function of T cells and B cells Suppressor T Cells - Inhibit function of T cells and B cells

B Cells • Produce antibody (humoral)-mediated

immunity • Make up 10–15% of circulating lymphocytes• Differentiate into plasma cells

Plasma Cells• Produce and secrete antibodies

(immunoglobin proteins) • The binding of a specific antibody to its

specific target antigen initiates antibody-mediated immunity

Natural Killer (NK) Cells

• Provides immunological surveillance• Also called large granular lymphocytes • Make up 5–10% of circulating lymphocytes• Attacks foreign cells, infected cells, and

cancerous cells

The Immune System• All body cells and tissues involved in defense

of the body against pathogens and the production of immunity:

IMMUNITY: the ability of the body to resist disease

• Two categories of Defense Mechanisms– Nonspecific Defenses– Specific Defenses

Pathogens• Microscopic organisms that cause

disease:– viruses– bacteria– fungi– parasites

• Each attacks in a specific way

Nonspecific Defenses • Block or attack any potential

infectious organism• Cannot distinguish one attack from

another

Types of Nonspecific Resistance

1. Physical barriers2. Phagocytic cells3. Immunological surveillance4. Interferons5. Complement6. Inflammation7. Fever

The 7 Nonspecific

Defense Mechanism

ss

Physical Barriers • Outer layer of skin• Hair• Epithelial layers of internal

passageways• Secretions that flush away

materials:– sweat glands, mucus, and urine

• Secretions that kill or inhibit microorganisms:– enzymes, antibodies, and stomach

acids

2 Classes of Phagocytic Cells

• Microphages:– neutrophils and eosinophils– Leave the bloodstream to fight

infections

• Macrophages:– large phagocytic cells derived from

monocytes– May be fixed or free moving

Immunological Surveillance

• Is carried out by natural killer (NK) cells

• Identifies, attaches, and kills (via lysis) abnormal cells (cancer cells, cells infected with viruses)

Interferons• Proteins (cytokines) released by

activated lymphocytes and macrophages

• Chemical messengers released by tissue cells:– to coordinate local activities– to act as hormones to affect whole body– stimulate NK cells– slow inflammation– stimulate macrophage activity

Complement• Plasma contains 11

special complement (C) proteins:– that complement

antibody action by:1. Stimulation of inflammation2. Attraction of phagocytes3. Enhancement of phagocytosis

by opsonization4. Destruction of target cell

membranes

Inflammation• Also called inflammatory response • A localized response• Triggered by any stimulus that kills

cells or injures tissue• Symptoms:

– Swelling (tumor)– Redness (rubor)– Heat (calor)– Pain (dolor)

3 Effects of Inflammation

1. Temporary repair and barrier against pathogens

2. Slows spread of pathogens into surrounding areas

3. Mobilization of local and systemic defenses:

– and facilitation of repairs (regeneration)

Fever• A maintained body temperature

above 37°C (99°F)• Pyrogen = a substance that causes

the hypothalamus to raise body temperature. (ie: circulating pathogens, toxins, pyrogens released by active macrophages, cytokines

• Increases metabolism and cellular activities to stimulate repair

• >104°can cause systemic damage

Specific and Nonspecific Defenses

Specific Defenses• Specific resistance (immunity):

– responds to specific antigens– with coordinated action of T cells

and B cells

• Antigens: unique targets found on cell membranes which identify any pathogen or foreign compound as “not self”

4 Properties of Immunity

• Specificity- Each T or B cell responds only to a specific antigen and ignores all others

• Versatility-The body produces many types of lymphocytes. Each fights a different

type of antigen. Active lymphocyte clones itself to fight specific antigen.

• Memory-Some active lymphocytes (memory cells) stay in circulation and provide immunity against new exposure

• Tolerance-Immune system ignores “normal” antigens

Figure 22–14

Forms of Immunity

Forms of Immunity• Innate:

– present at birth, genetically determined

• Acquired – after birth– produced after exposure to antigen

Acquired Immunity • Active:

– antibodies develop after exposure to antigen

• Passive:– antibodies are transferred from

another source

Active Immunity • Naturally acquired:

– through environmental exposure to pathogens

• Induced:– through vaccines containing

pathogens (antigens) or antibodies to combat infection

Passive Immunity • Naturally acquired:

– antibodies acquired from the mother

• Induced:– by an injection of antibodies

B Cell Sensitization and Activation

Immune Disorders• Autoimmune disorders• Immunodeficiency disease• Allergies

Autoimmune Disorders

• A malfunction of system that recognizes and ignores “normal” antigens

• Activated B cells make autoantibodies against body cells– Lupus– Rheumatoid arthritis– Insulin-dependent diabetes mellitus

Immunodeficiency Diseases

• Viral infections such as HIV:– can result in AIDS

• Immunosuppressive drugs or radiation treatments:

– can lead to complete immunological failure

Allergies

• Inappropriate or excessive immune responses to antigens

• Allergens:– antigens that trigger allergic

reactions

4 Categories of Allergic Reactions

• Type I:– immediate hypersensitivity (allergies)

• Type II:– cytotoxic reactions (blood type

incompatibility)

• Type III:– immune complex disorders (tissue damage)

• Type IV:– delayed hypersensitivity (poison oak)

Antihistamine Drugs

• Block histamines released by MAST cells

• Can relive mild symptoms of immediate hypersensitivity

Stress and the Immune Response

• Glucocorticoids:– secreted to limit immune response – long-term secretion (chronic stress):

•inhibits immune response•lowers resistance to disease

Aging and the Immune Response

• Immune system deteriorates with age, increasing vulnerability to infections and cancer.