Anatomy & Physiology

Anatomy & Physiology Study Guide The smallest lymphatic capillaries • Lymph flows along a network of lymphatic vessels, lymphatic capillaries (terminal lymphatics) being the smallest, and empties into the thoracic duct and the right lymphatic duct. • The three classes of lymphocytes are T (thymus-dependent) cells, B (bone marrow-derived) cells, and NK (natural killer) cells. Virus-infected or foreign cells get attacked by the Cytocix T cells which provide cell-mediated (cellular) immunity. The regulation and coordination of the immune response are performed by the T cells (helper and suppressor). • B cells can differentiate into plasma cells, which produce and secrete antibodies that react with specific chemical targets called antigens. Antibodies in body fluids are called immunoglobulins. B cells are responsible for antibody-mediated (humoral) immunity. • NK cells (also called large granular lymphocytes) attack foreign cells, normal cells infected with viruses, and cancer cells. NK cells provide immunological surveillance. • Lymphocytes continuously roam in and out of the blood through the lymphoid tissues and organs. Lymphopoiesis (lymphocyte production) involves the bone marrow, thymus, and peripheral lymphoid tissues. • Lymphoid tissues are connective tissues dominated by lymphocytes. In a lymphoid nodule, the lymphocytes are densely packed in an area of loose connective tissue. • The lymphoid tissue embedded within the organs of the digestive system is called mucosa- associated lymphoid tissue (MALT). • Important lymphoid organs include the lymph nodes, the thymus, and the spleen. Lymphoid tissues and organs get distributed into areas most vulnerable to injury or invasions. • Lymph nodes are encapsulated masses of lymphoid tissue. The deep cortex is dominated by T cells; the outer cortex and medulla contain B cells. • Located behind the sternum is the thymus, located in the anterior mediastinum. Reticular epithelial cells scattered among the lymphocytes maintain the blood-thymus barrier and secrete thymic hormones. • The largest mass of lymphoid tissue is located in the adult spleen. The cellular components form the pulp of the spleen. Red pulp contains large numbers of red blood cells, and white pulp resembles lymphoid nodules. • The lymphatic system is a major component of the body’s defenses, which are classified as either nonspecific defenses, which protect without distinguishing one threat from another, or (2) specific defenses, which protect against particular threats only. Nonspecific defenses do not discriminate between potential threats and respond the same regardless of the invader: • Nonspecific defenses prevent the approach, deny the entry, or limit the spread of living or nonliving hazards. Achieve Page 291 of 368 ©2018