Chapter 21- Immune system

not an organ system, but a cell population that inhabits all organs and defends the body from agents of disease

-fluid recover -immunity -lipid absorption

• Fluid continually filters from the blood capillaries into the tissue spaces • Blood capillaries reabsorb 85% • 15% (2 to 4 L/day) of the water and about half of the plasma proteins enter the lymphatic system and then are returned to the bloo

• Excess filtered fluid (lymph) picks up foreign cells and chemicals from the tissues • Passes through lymph nodes where immune cells stand guard against foreign matter • Activates a protective immune response

• Lacteals in small intestine absorb dietary lipids that are not absorbed by the blood capillaries

-Lymphatic capillaries penetrate almost all body tissues, except cartilage, cornea, bone, and bone marrow. -They have a closed-end structure with endothelial cells overlapping like roof shingles. -Anchoring filaments attach the cells to surrounding tissue. -Large gaps between cells allow bacteria and cells to enter. -Valve-like flaps in the endothelium open with high interstitial fluid pressure and close when it’s low

receives lymph from right arm, right side of head and thorax; empties into right subclavian vein

larger and longer, begins as a sac in abdomen called the cisterna chyli

receives lymph from below diaphragm, left arm, left side of head, neck, and thorax; empties into left subclavian vein

collect from thoracic duct

Lymph flows at low pressure and slow speed, driven by rhythmic contractions of lymphatic vessels (stimulated by vessel stretching), skeletal muscle and thoracic pumps, arterial pulsations, and the suction effect of rapidly flowing blood in subclavian veins, with valves preventing backflow. Exercise greatly enhances lymphatic return

-neutrophils -natural killer cells -T lymphocytes -B lymphocytes -dendritic cells -reticular cells

antibacterial

large lymphocytes that attack and destroy bacteria, transplanted tissue, host cells infected with viruses or that have turned cancerous

mature in thymus, helper, cytotoxic, and regulator

activation causes proliferation and differentiation into plasma cells that produce antibodies

branched, mobile antigen-presenting cells (APCs) found in epidermis, mucous membranes, and lymphatic organs; alert immune system to pathogens that have breached the body surface

branched stationary APCs that contribute to the stroma (connective tissue framework) of a lymphatic organ

• Large, avidly phagocytic cells of connective tissue • Develop from monocytes or other macrophages • Phagocytize tissue debris, dead neutrophils, bacteria, and other foreign matter • Process foreign matter and display antigenic fragments to certain T cells alerting immune system to the presence of the enemy • Become antigen-presenting cells (APCs) when they do this

• Dense masses of lymphocytes and macrophages that congregate in response to pathogens • Constant feature of the lymph nodes, tonsils, and appendix • Aggregated lymphoid nodules: dense clusters in the ileum, the distal portion of the small intestine

-Lymphatic organs are anatomically well-defined -Have connective tissue capsule or partial capsule that separates lymphatic tissue from neighboring tissues

• Red bone marrow and thymus • Site where T and B cells become immunocompetent (become mature): able to recognize and respond to antigens

• Lymph nodes, tonsils (patches of lymphatic tissue but distinct), and spleen • Immunocompetent cells populate these tissues

• Soft, loosely organized, highly vascular material • Separated from osseous tissue by endosteum of bone • As blood cells mature, they push their way through the reticular and endothelial cells to enter the sinus and flow away in the bloodstream