The Lymphatic System and Immunity

• The immune system protects the body from foreign invaders and diseases.

Distinguishing Features of the Lymphatic System

• Lymphatic vessels resemble veins and carry lymph throughout the body while maintaining fluid balance, transporting fats from the digestive tract, and contributing to immune defense.
• Lymphatic nodules are small, unencapsulated clusters of lymphoid tissue found in connective tissue like tonsils and Peyer's patches, and are rich in lymphocytes and macrophages.
• Lymphatic organs include lymph nodes that filter lymph, the spleen that filters blood, and the thymus for T-cell maturation, all of which are encapsulated and serve immune roles.

Nonspecific (Innate) Resistance to Disease

• Inflammation is a protective tissue response to injury or infection, characterized by redness, heat, swelling, and pain, which isolates and removes harmful agents and initiates repair.
• Fever is an increase in body temperature due to pyrogens, enhancing immune responses and inhibiting pathogen growth.
• Phagocytes, such as white blood cells like neutrophils and macrophages, engulf pathogens, debris, and foreign particles, and are essential components of innate immunity.

Specific (Adaptive) Immunity

• An antigen is a foreign molecule, typically a protein or polysaccharide on a pathogen's surface, that elicits an immune response.
• Antibodies, also called immunoglobulins, are Y-shaped proteins produced by B-cells that bind specific antigens for neutralization or destruction.
• Lymphocytes are key immune cells, including B-cells that produce antibodies, and T-cells that kill infected cells or help regulate immune responses.
• Humoral (antibody-mediated) immunity involves B-cells and circulating antibodies that neutralize extracellular pathogens.
• Cellular (cell-mediated) immunity involves T-cells that directly destroy infected or abnormal cells, and is especially effective against intracellular pathogens.