chapter 14: the lymphatic system and immunity. functions of the lymphatic system produce, maintain,...
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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
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
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
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
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 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
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
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