LYMPHATIC SYSTEM
Chapter 20 Overview
Focus on the lymphatic system and its role in immunity.
Key cells involved:
Cytotoxic T cells: attack cancer and infected cells.
B lymphocytes (B cells): involved in antibody-mediated immunity.
T lymphocytes (T cells): engage in cell-mediated immunity.
Functions of the Lymphatic System
Three Major Functions:
Return excess tissue fluid to blood.
Absorb fats from the digestive system.
Defend the body against disease (immunity).
Tissue Fluid Dynamics:
Importance of capillary beds in fluid exchange:
Arterial End: Hydrostatic pressure > osmotic pressure (net filtration pressure of 13 mmHg pushing fluids out).
Venule End: Osmotic pressure > hydrostatic pressure (net filtration pressure of -7 mmHg pulling fluids back in).
Results in excess fluid being picked up by lymphatic capillaries.
Lymphatic Capillaries and Vessels
Lymph: clear fluid similar to blood, but lacks red blood cells.
Movement of lymph is facilitated by:
Skeletal muscle action (milking effect).
Pressure changes during breathing.
One-way valves prevent backflow.
Lymphatic vessels drain into larger structures (trunks & ducts), ultimately returning lymph to venous circulation via
Right lymphatic duct (right side of body)
Thoracic duct (left side and rest of the body).
Major Components of the Lymphatic System
Lymphatic Trunks include:
Right & left jugular trunks (near jugular vein).
Right & left subclavian trunks (near the clavicle).
Right & left bronchomediastinal trunks (in the thorax).
Left lumbar trunk & intestinal trunk (related to the digestive system).
Cisterna chyli: collects lymph from lumbar and intestinal trunks.
Lymphoid Cells, Tissues, and Organs
Key Cells:
Lymphocytes:
T cells (cell-mediated immunity).
B cells (antibody-mediated immunity).
Macrophages: derived from monocytes, function in phagocytosis.
Major Tissues: Reticular connective tissue (similar to areolar connective tissue).
Major Organs:
Lymph Nodes: filter lymph, activating immune response.
Spleen: largest organ, involved in blood filtration and immune activation.
Thymus: site of T cell maturation, atrophies with age.
Tonsils and MALT: trap pathogens, helping to develop immune response.
Leukopoiesis Process
Stem cells in bone marrow give rise to myeloid and lymphoid lines.
Lymphoid Line: develops into lymphoblasts, prolymphocytes, to B and T lymphocytes.
Myeloid Line: develops into monocytes and granulocytes (eosinophils, basophils, neutrophils).
Lymph Nodes Structure and Function
Located throughout the body but clustered in key areas (cervical, axillary, inguinal).
Biological filters that trap pathogens, aiding in immune activation.
The Spleen
Largest lymphoid organ, behind the stomach.
Functions in:
Immune defense (filtering blood).
Hematopoiesis in the fetus.
Blood reservoir, and destruction of old RBCs.
Thymus Overview
Key organ for T cell maturation; atrophy occurs after puberty.
Releases thymosin, essential for T cell function.
Antigen Definition and Response
Antigens: substances provoking an immune response.
Antigen presenting cells (APCs): show antigen fragments to T cells, initiating adaptive immunity.
T Cell Activation
Interaction between MHC and T cell leads to activation and proliferation.
Helper T cells stimulate B cells and leukocytes, cytotoxic T cells directly kill infected cells.
B Cell Activation and Antibody Production
B cells process antigens and are activated by helper T cells.
Differentiate into plasma cells (produce antibodies) and memory B cells (long-term immunity).
Types of Antibodies (Immunoglobulins)
IgG: Most abundant; crosses placenta; involved in opsonization.
IgA: Found in secretions (saliva, tears).
IgM: First antibody produced; good agglutination agent.
IgE: Triggers allergic reactions.
IgD: Functions in B cell sensitization.
Primary vs Secondary Immune Responses
Primary Response: slower, initial exposure to antigen.
Secondary Response: faster, stronger reaction upon re-exposure due to memory cells.
Active vs Passive Immunity
Active Immunity: body produces its own antibodies (natural exposure or vaccination).
Passive Immunity: antibodies received from external sources (e.g., mother to infant, or antibody therapies).
Key Difference: Active produces memory cells; Passive does not.
The lymphatic system plays a crucial role in immunity, featuring key cells such as cytotoxic T cells that attack cancer and infected cells, B lymphocytes (B cells) that are involved in antibody-mediated immunity, and T lymphocytes (T cells) that engage in cell-mediated immunity.
The lymphatic system has three major functions: it returns excess tissue fluid to the bloodstream, absorbs fats from the digestive system, and defends the body against disease. The dynamics of tissue fluid are vital, as capillary beds allow for fluid exchange. At the arterial end, hydrostatic pressure exceeds osmotic pressure, resulting in a net filtration pressure of 13 mmHg that pushes fluids out. Conversely, at the venule end, osmotic pressure exceeds hydrostatic pressure, creating a net filtration pressure of -7 mmHg that pulls fluids back in, leading to excess fluid being picked up by lymphatic capillaries.
Lymph is a clear fluid similar to blood, but it lacks red blood cells. The movement of lymph is facilitated by several factors, including skeletal muscle action (referred to as the milking effect), pressure changes during breathing, and one-way valves that prevent backflow. Lymphatic vessels drain into larger structures like trunks and ducts, ultimately returning lymph to venous circulation via the right lymphatic duct (for the right side of the body) and the thoracic duct (for the left side and the rest of the body).
The major components of the lymphatic system include lymphatic trunks, such as right and left jugular trunks (near the jugular vein), right and left subclavian trunks (near the clavicle), right and left bronchomediastinal trunks (in the thorax), as well as the left lumbar trunk and intestinal trunk, which are related to the digestive system. The cisterna chyli serves as a collection point for lymph from the lumbar and intestinal trunks.
Key cells in lymphoid tissues include lymphocytes such as T cells (involved in cell-mediated immunity) and B cells (involved in antibody-mediated immunity), as well as macrophages, which are derived from monocytes and function in phagocytosis. The major tissues consist of reticular connective tissue, while the major organs of the lymphatic system include lymph nodes, the spleen, the thymus, tonsils, and mucosa-associated lymphoid tissue (MALT), all of which play significant roles in trapping pathogens and activating the immune response.
The process of leukopoiesis begins with stem cells in the bone marrow that give rise to myeloid and lymphoid lines. The lymphoid line develops into lymphoblasts and prolymphocytes, which further differentiate into B and T lymphocytes, while the myeloid line develops into monocytes and granulocytes (eosinophils, basophils, and neutrophils).
Lymph nodes are located throughout the body and are clustered in key areas such as cervical, axillary, and inguinal regions. They act as biological filters that trap pathogens, aiding in immune activation. The spleen, the largest lymphoid organ located behind the stomach, functions in immune defense by filtering blood, plays a role in hematopoiesis during fetal development, serves as a blood reservoir, and is involved in the destruction of old red blood cells.
The thymus is a vital organ for T cell maturation and undergoes atrophy after puberty. It releases thymosin, which is essential for T cell function. Antigens, which are substances provoking an immune response, are presented to T cells by antigen-presenting cells (APCs), initiating adaptive immunity.
T cell activation occurs through the interaction between major histocompatibility complex (MHC) molecules and T cells, leading to their activation and proliferation. Helper T cells stimulate B cells and leukocytes, while cytotoxic T cells directly kill infected cells. B cell activation involves processing antigens with the help of helper T cells, after which they differentiate into plasma cells that produce antibodies and memory B cells that provide long-term immunity.
There are several types of antibodies (immunoglobulins) in the immune response. IgG is the most abundant antibody, crosses the placenta, and is involved in opsonization. IgA is found in secretions like saliva and tears, while IgM is the first antibody produced and is effective as an agglutination agent. IgE triggers allergic reactions, and IgD functions in B cell sensitization.
The primary immune response is slower and occurs during the initial exposure to an antigen, while the secondary response is faster and stronger upon re-exposure due to the presence of memory cells. Active immunity occurs when the body produces its own antibodies through natural exposure or vaccination, whereas passive immunity involves receiving antibodies from external sources, such as from mother to infant or through antibody therapies. The key difference is that active immunity results in the production of memory cells, while passive immunity does not.