The Lymphatic and Immune System

The Lymphatic and Immune System

• The lymphatic system consists of lymphatic vessels and organs, maintaining homeostasis and part of the immune system.
• Lymphatic capillaries absorb excess interstitial fluid and fats from the digestive tract, transporting them to the bloodstream.
• Lymphoid organs defend the body against disease.
• Lymphatic vessels form a one-way system moving interstitial fluid to the cardiovascular system.
• Interstitial fluid is mostly water, containing nutrients, electrolytes, oxygen, hormones, enzymes, and cellular waste.
• Lymphatic organs are primary and secondary.
• Primary lymphatic organs are red bone marrow and the thymus.
• Red bone marrow produces all blood cells; children have it in many bones, adults in specific bones (sternum, vertebrae, ribs, pelvic girdle, humerus, femur).
• Red bone marrow produces red blood cells and five white blood cell types: neutrophils, eosinophils, basophils, lymphocytes, monocytes.
• Lymphocytes are divided into B cells (maturing in bone marrow, reacting to body cells are destroyed) and T cells (maturing in thymus).
• The thymus is a soft, bilobed organ between the trachea and the sternum, decreasing in size with age.

Thymus Function

• Produces hormones (like thymosin) aiding T lymphocyte maturation.
• Only about 5% of T cells leave the thymus, proving they can attack pathogens without attacking body cells.
• Without mature T cells, the body can't respond to specific infections.

Secondary Lymphatic Organs

• Spleen filters blood, located in the upper left of the abdomen.
• Lymph nodes are along lymphatic vessels, containing lymph, lymphocytes, and macrophages that fight pathogens and cancer cells.

Innate (Non-Specific) Immunity

• Physical and chemical barriers (skin, mucous membranes, perspiration, saliva, tears (with lysozyme), stomach and vaginal acid, microbiome).
• Inflammatory response using neutrophils and macrophages to surround and kill pathogens (symptoms include redness, heat, swelling, pain).

Adaptive Immunity

• Immune system's ability to specifically kill or remove foreign substances, pathogens, and cancer cells.
• Primarily depends on B and T cells, each with a specific receptor for a particular antigen.
• Cell-mediated immunity (T cells) targeting cells with specific antigens.
• Antibody-mediated immunity (B cells) generating antibodies.
• Helper T cells activating cytotoxic T cells and plasma cells, which create antibodies.

Antibody Structure and Function

• Y-shaped with two antigen-binding sites.
• Antibodies bind to antigens, preventing harmful actions, or signaling other white blood cells.
• Antibody classes (IgG, IgM, IgA, IgD, IgE) have different roles and locations.

Complement System

• Blood plasma proteins enhancing immune response (can trigger mast cells releasing histamine, attract phagocytes, or directly bind to bacteria and cause them to burst).
• Interferons-proteins produced by infected cells preparing uninfected cells for viral infection.
• Antigen-foreign body, large protein structures recognized by the immune system.

Adaptive Immunity Pathways

• Cell-mediated pathway where T cells target and destroy cells with specific antigens.
• Antibody-mediated pathway (humoral) where B cells create antibodies.
• Helper T cells contact antigens and release cytokines, calling cytotoxic T cells to the area. Cytotoxic T cells may phagocytize cells or trigger apoptosis.

Active and Passive Immunity

• Active immunity- developing antibodies after infection or vaccination.
• Passive immunity- receiving pre-made antibodies (e.g., from mother to fetus, serum injection).

Immune System Disorders

• Organ rejection occurs when the immune system identifies transplanted organs as foreign.
• Severe combined immunodeficiency disease (SCID) is characterized by inadequate or lacking antibody and cell mediated immune responses.
• Autoimmune diseases result from the immune system attacking the body's own tissues (e.g., rheumatoid arthritis, systemic lupus erythematosus, myasthenia gravis).
• Anaphylactic shock is a life-threatening, immediate allergic response.
• Allergies are hypersensitivity responses to harmless substances (allergens).