Chapter 14 – The Lymphatic System and Immunity The other circulatory system

Summary Lymphatic system Immune system Fluid Vessels Nodes and Nodules Organs Immune system Nonspecific Specific Cells Mechanisms

Lymphatic System Function – responsible for returning tissue fluid to the blood and for protecting the body against foreign material. Lymph is a specialized fluid which is formed in the tissue spaces = interstitial fluid. Contains excess fluid and protein molecules that cannot enter or return through the capillary walls.

Lymphatic System Lymphatic vessels Lymph capillaries – blind ended vessels that are very permeable; collect tissue fluids and proteins in the tissues.

Lymphatic System Vessels cont’d Lymph venules then veins collect fluid from the capillaries. Ducts – large vessels that drain the lymph into the blood in veins (subclavian) in the neck area. Right lymphatic duct Thoracic duct

Lymphatic System Vessels Cisterna chyli – enlarged pouch-like structure formed by the union of the lower body lymphatic vessels. Lower portion of the thoracic duct in the abdomen; serves as a storage area for lymph that is moving toward its point of entry into the venous system.

Lymphatic System Fluid is moving under low pressure and against gravity – How? Smooth muscle in the walls of the larger vessels contracts and moves fluid upward. Skeletal muscle pump Pressures in thoracic cavity

Lymphatic System Lymph Nodes Clusters of small encapsulated masses of lymphatic tissue located at strategic spots in the lymph system. They may be the size of a pin head or a lima bean. Lymph enters the node through afferent vessels (usually more than one) and leaves through a single efferent vessel.

Lymphatic System Lymph Nodes Serve to filter and trap bacteria, cancer cells and other foreign material picked up by the lymphatic vessels. Fixed macrophages in the nodes phagocytize (eat) these particles. Fixed plasma cells produce antibodies in response to foreign material and these antibodies then circulate in the blood stream. **Also produce lymphocytes and monocytes.

Lymphatic System Lymph Nodes Significant groups: cervical, axillary and inguinal. Clinical significance:

Lymphatic System Lymph Nodules Smaller masses of lymphatic tissue (not encapsulated) found just beneath the epithelium of all mucous membranes. Mucous membranes are located at openings to the environment – respiratory, digestive, urinary and reproductive systems. Why is this a good spot for lymph tissue?

Lymphatic System Special Lymph Nodules Peyer’s patches located in the small intestine. Tonsils – located in the pharynx form a protective ring under the mucous membranes in the mouth and back of throat. Palatine – Pharyngeal – Lingual –

Lymphatic System Organs Thymus – located inferiorly to the thyroid gland in the mediastinum. Produces T-lymphocytes (T-cells) and secretes thymosin and other hormones that stimulate their development. The thymus is critical to immunity in the fetus and infant. The thymus shrinks with age but is still active.

Lymphatic System Spleen Largest lymphoid organ in the body located in the upper left quadrant of the abdomen, lateral to the stomach, just below the diaphragm. Functions:

Lymphatic System Spleen Functions: Splenectomy? Fixed macrophages, reticuloendothelial cells, phagocytize pathogens in the blood. Also phagocytize and destroy old RBCs producing bilirubin. Stores about 1 pint of blood – hemorrhage Splenectomy? Liver and red bone marrow will compensate to remove old RBC’s and lymph nodes and nodules will produce lymphocytes and monocytes, etc.

Immune System Immunity – the body’s ability to destroy pathogens or other foreign material and prevent further cases of certain infectious diseases. Types of Immunity:

Immunity Non-specific (innate) immunity - maintained by mechanisms that attack any abnormal substance that threatens the body; general protection. Barriers: Skin, mucous membranes (and mucus), cilia. Lysozymes in tears and saliva. SQ and areolar connective tissue WBC phagocytize bacteria.

Immune System Specific immunity Includes protective mechanisms that confer very specific protection against certain types of invading materials. Involves “memory” – when the body is attacked the first time a disease develops; the next time no disease signs/symptoms develop; i.e. the body is immune.

Immune System Specific Immunity - Inherited Genetic, inborn immunity is the result of our genetic make-up, i.e. we do not get distemper and dogs don’t get measles (species immunity). This type does not involve antibodies and the efficiency does not increase with subsequent exposures.

Immune System Specific Immunity - Acquired Natural – exposure to the causative agent is not deliberate. Active – Passive –

Immune System Specific Immunity – Acquired Artificial – exposure to the causative agent is deliberate. Active - injection of the agent (vaccine) results in production of your own antibodies and memory cells. Passive – injection of protective material (antibodies) that was developed by another individual’s immune system (gamma globulins or immune globulins).

Immune System - Cells Phagocytes – neutrophils, monocytes and macrophages, derived from bone marrow, carry out ingestion and digestion of foreign cells or particles. Monocytes develop into macrophages. Macrophages – some wander and some are fixed; example Kupffer’s cells in the spaces between liver cells.

Immune System - Cells Lymphocytes – most numerous cells of the immune system; responsible for antibody production T-cells – produced in the bone marrow and thymus of the embryo. They mature in the thymus and migrate to the spleen, lymph nodes and nodules.

Immune System - Cells Lymphocytes B-cells – produced in the bone marrow When activated by an antigen, they become plasma cells that produce antibodies. They also can become memory cells that remain in reserve until a stimulus by the same antigen is repeated and then produce antibodies.

Immune System Cells Lymphocytes Natural Killer Cells (Killer T-cells) – smaller in number but can attack many types of pathogens and tumor cells. Formed from activated T-cells. Mechanism : disrupt cell membranes of foreign cells.

Immune System - Cells Review Definitions: Antigen – chemical markers that identify cells. Each cells has its own set of markers. Antibodies (immune or gamma globulins) Proteins produced by plasma cells in response to foreign antigens; each one is specific for a certain antigen. Mechanism: When bound to an antigen they cause agglutination (clumping) of the material. Also the mechanism for allergic responses.

Mechanisms of Immunity Recognition of an antigen as foreign – accomplished by macrophages and helper T-cells. Foreign antigen is phagocytized by a macrophage. Macrophage presents antigen material on its cell membrane. Helper T-cell is exposed to this part of the macrophage membrane and becomes sensitized.

Mechanisms of Immunity Once an antigen has been recognized, the activated helper T cells initiate one or both immune mechanisms. Cell Mediated Immunity Humoral Immunity

Mechanisms of Immunity Cell- mediated Immunity – no antibody produced T-cells activated by foreign material form memory T-cells and killer (cytotoxic) T-cells. Memory cells will remember the specific antigen and become active if it enters body again. Killer T-cells chemically destroy foreign antigens (disrupt cell membranes).

Mechanisms of Immunity Cell-mediated immunity T-cells cont’d Killer T-cells also produce cytokines – chemicals that attract macrophages to an area to promote phagocytosis. Suppressor T-cells stop the immune response once the antigen has been destroyed.

Mechanisms of Immunity Humoral Immunity – involves production of antibodies. Recognition of foreign antigen by macrophages and activation of helper T-cells. Sensitized helper T-cell presents antigen to B-cells B-cells activate the memory B cells and plasma cells. The plasma cells then produce antibodies.

Mechanisms of Immunity Humoral Immunity Antibodies bind to antigens forming an antigen-antibody complex. Complex is labeled for phagocytosis by macrophages = opsonization. Complement fixation – complement binds to complex and is destroyed by lysis.

Immune System OYO Read: Aids, p 332 Interferon, p 328 (Chemical defenses) Vaccines, pp 335 and 337