Lymphatic System

Components Lymph : clear, colorless fluid ( there is not red blood cell) The fluid within the lymph capillaries and vessels is known as lymph, The composition of lymph like blood plasma but in different concentration ( water, Na, K ….etc )

– lymphatics Vessels Lymphatic tissue Lymphatic organ –Functions Return tissue fluid to the bloodstream Transport fats from the digestive tract to the bloodstream defense

Lymphatic Vessels Lymphatic capillaries – diffuse, highly permeable due to presence of: –Minivalves loosely overlapping endothelial cells –Collagen fiber attachment to surrounding structures prevents collapse of capillary Lymphatic collecting vessels like veins but thinner walled w/ more valves and anastomoses Lymphatic trunks – lumbar, bronchomediastinal, subclavian, jugular and intestinal Lymphatic ducts – Right Lymphatic Duct & Thoracic Duct

Lymphatic Capillaries During inflammation, lymph capillaries can absorb: –Cell debris –Pathogens –Cancer cells Cells in the lymph nodes cleanse and “examine” this debris Lacteals – specialized lymph capillaries present in intestinal mucosa –Absorb digested fat and deliver chyle to the blood

Lymph Capillaries

Lymphatic Vessels

Lymph Tissue –3 types Diffuse lymphatic tissue –No capsule present –Found in connective tissue of almost all organs Lymphatic nodules –No capsule present –Oval-shaped masses –Found singly or in clusters Lymphatic organs –Capsule present –Lymph nodes, spleen, thymus gland

Lymphoid Cells Lymphocytes are the main cells involved in the immune response Two main varieties: –T cells –B cells

Lymphocytes T cells –Manage the immune response –Attack and destroy foreign cells B cells –Produce plasma cells, which secrete antibodies –Antibodies immobilize antigens

Other Lymphoid Cells Macrophages – phagocytize foreign substances and help activate T cells Dendritic cells – spiny-looking cells with functions similar to macrophages Reticular cells – fibroblast–like cells that produce a stroma, or network, that supports other cell types in lymphoid organs

Lymph Nodes –Oval structures located along lymphatics –Enclosed by a fibrous capsule –Cortex = outer portion Germinal centers produce lymphocytes –Medulla = inner portion Medullary cords –Lymph enters nodes through afferent lymphatics, flows through sinuses, exits through efferent lymhpatic

Lymph Nodes Two basic functions: –Filtration – macrophages destroy microorganisms and debris –Immune system activation – monitor for antigens and mount an attack against them

Structure of a Lymph Node Figure 20.4a, b

Other Lymphoid Organs The spleen, thymus gland, and tonsils Peyer’s patches and bits of lymphatic tissue scattered in connective tissue All are composed of reticular connective tissue All help protect the body Only lymph nodes filter lymph

Tonsils Simplest lymphoid organs; form a ring of lymphatic tissue around the pharynx Location: –Palatine tonsils – either side of the posterior end of the oral cavity –Lingual tonsils – lie at the base of the tongue –Pharyngeal tonsil – posterior wall of the nasopharynx –Tubal tonsils – surround the openings of the auditory tubes into the pharynx

Tonsils Lymphoid tissue of tonsils contains follicles with germinal centers Tonsil masses are not fully encapsulated Epithelial tissue overlying tonsil masses invaginates, forming blind-ended crypts Crypts trap and destroy bacteria and particulate matter

Tonsils

Spleen –Largest lymphatic organ –Located on the left side of the abdominal,between the stomach & diaphragm –Histology Red pulp contains all the components of circulating blood White pulp is similar to lymphatic nodules –Functions Filters blood –Stores blood –Site of lymphocyte proliferation –Immune surveillance and response

Spleen

Thymus Gland –Location – behind the sternum in the mediastinum –The capsule divides it into 2 lobes –Development Infant – conspicuous Puberty – maximum size Maturity – decreases in size –Function Differentiation and maturation of T cells

Thymus Gland

Function of the Lymphatic System –Defense against harmful organisms and chemicals –2 types of defense Nonspecific Specific –Specific defense = immunity Humoral immunity involves B cells that become plasma cells which produce antibodies that bind with specific antigens. Cell-mediated immunity involves T cells that directly destroy foreign cells

Derivation and Distribution of Lymphocytes