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 Organs Spleen 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 Lymphocytes 1.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 Types Cytotoxic 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 barriers 2.Phagocytic cells 3.Immunological surveillance 4.Interferons 5.Complement 6.Inflammation 7.Fever

The 7 Nonspecific Defense Mechanismss

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 inflammation 2.Attraction of phagocytes 3.Enhancement of phagocytosis by opsonization 4.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

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.