Lymph Transport and Immunity Overview

Lymph Transport and Immunity

• Lymph transport system comprised of lymphatic vessels and lymphoid organs
• The lymphatic system maintains homeostasis by collecting excess fluid from tissues and returning it to the bloodstream.
• Lymphatic capillaries absorb fats from the digestive system through lacteals and transports them to the bloodstream.
• Lymph circulates one way from capillaries to vessels, eventually flowing into a lymphatic duct which drains into a subclavian vein,

Lymphoid Organs

• Lymph nodes have cortex and medulla regions. Lymphocytes congregate in the cortex when fighting pathogens. Macrophages cleanse lymph in the medulla. Lymph Nodes are named for their location.

• Tonsils are patches of lymphatic tissue positioned around the pharynx, initially encountering pathogens entering via the nose and mouth.

• The spleen is located in the upper left abdominal cavity, positioned beneath the diaphragm. It cleanses the blood.

• The thymus gland sits along the trachea behind the sternum in the upper thoracic cavity. It produces thymic hormones.

• Red bone marrow serves as the origin for all blood cells and is the maturation site for most white blood cells

Immune System (Non-Specific Defenses)

• Barriers like skin and mucous membranes (including ciliated cells in the respiratory tract) form a physical defense against pathogens.

• The inflammatory response is triggered when damaged cells and mast cells release histamine and kinins. Capillaries dilate, allowing neutrophils and monocytes to migrate to the injury site and engulf pathogens. Monocytes differentiate into macrophages.

Immune System (Specific Defenses)

• Antigens are foreign substances that trigger the immune response.

• Lymphocytes recognize antigens through specific receptors.

• B cells produce antibodies that bind to and inactivate antigens.

• T cells directly attack cells that display non-self proteins.

Antibody-Mediated Immunity (B lymphocytes)

• The clonal selection theory explains how an antigen selects a specific lymphocyte to undergo clonal expansion and produce more lymphocytes for the immune response.
• Memory B cells enable the body to respond faster and stronger to subsequent encounters with the same antigen.

Cell-Mediated Immunity (T cells)

• Cytotoxic T cells directly destroy antigen-carrying cells by releasing perforins which create pores in the target cell causing it to die.
• Helper T cells regulate the immune response by releasing cytokines.

Active versus Passive Immunity

• Active immunity develops through exposure to a pathogen or its components, developing memory lymphocytes for long-lasting protection.
• Passive immunity involves receiving pre-formed antibodies from another source, offering a temporary immune response.

Immunity Side Effects

• Allergies are hypersensitivities to substances that usually would not harm the body,. Immediate reactions are triggered by IgE antibodies, while delayed reactions involve memory T cells.
• Blood type reactions (ABO) can lead to agglutination if incompatible antigens and antibodies combine.
• Tissue rejection is the immune system's response to foreign tissue; cytotoxic T cells and antibodies target and destroy these tissues.
• Autoimmune diseases arise when the immune system mistakenly attacks the body's own cells.