Chapter 20 Lymphatic System OVERVIEW Two most important

Chapter 20: Lymphatic System

OVERVIEW Two most important functions: maintain fluid balance in the internal environment and immunity � Third function is to collect absorbed fat from the intestines and transport it to the systemic veins � Lymphatic system: component of the circulatory system; composed of lymph, lymphatic vessels, and isolated structures containing lymphoid tissue: lymph nodes, aggregated lymphoid nodules, tonsils, thymus, spleen, and bone marrow �

LYMPH AND INTERSTITIAL FLUID � Lymph (lymphatic fluid) Clear, watery fluid found in the lymphatic vessels � Closely resembles blood plasma in composition but has a lower percentage of protein � � Interstitial fluid Complex, organized fluid that fills the spaces between the cells and is part of the extracellular matrix � Resembles blood plasma in composition with a lower percentage of protein �

LYMPHATIC VESSELS (cont. ) � Structure � of lymphatic vessels Similar to veins except lymphatic vessels have thinner walls, have more valves, and contain lymph nodes � Functions of the lymphatic vessels � Remove high-molecular-weight substances and particulate matter from interstitial spaces

CIRCULATION OF LYMPH � From lymphatic capillaries, lymph flows through progressively larger lymphatic vessels to reenter blood at the junction of the internal jugular and subclavian veins

LYMPH NODES � Structure � Lymph of lymph nodes are oval-shaped structures enclosed by a fibrous capsule (Figure 20 -9) � Nodes are a type of biological filter � Once lymph enters a node, it moves slowly through sinuses to drain into the efferent exit vessel

LYMPH NODES (cont. ) � Locations of lymph nodes � Most lymph nodes occur in groups � Groups with greatest clinical importance are preauricular lymph nodes; � submental and submaxillary groups; � and superficial cervical, superficial cubital, axillary, iliac, and inguinal lymph nodes

LYMPH NODES (cont. ) � Lymph 1. Defense � Filtration 2. nodes perform two distinct functions Mechanical filtration: physically stopping particles from progressing further in the body Biological filtration: biologic activity of cells destroys and removes particles Hematopoiesis: lymphoid tissue is the site for the final stages of maturation of some lymphocytes and monocytes

LYMPHATIC DRAINAGE OF THE BREAST � Clinically important because cancer cells and infections can spread along lymphatic pathways to lymph nodes and other organs of the body � Distribution of lymphatics in the breast � Drained by two sets of lymphatic vessels � Lymphatics that drain the skin over the breast with the exception of the areola and nipple � Lymphatics that drain the underlying substance of the breast, as well as the skin of the areola and nipple

LYMPHATIC DRAINAGE OF THE BREAST (cont. ) � Lymph nodes associated with the breast � More than 85% of the lymph from the breast enters the lymph nodes of the axillary region � Remainder of lymph enters lymph nodes along the lateral edges of the sternum

TONSILS � Form a broken ring under the mucous membranes in the mouth and back of the throat—the pharyngeal lymphoid ring Palatine tonsils: located on each side of the throat � Pharyngeal tonsils: located near the posterior opening of the nasal cavity � Lingual tonsils: located near the base of the tongue � Tubal tonsils: located near the openings of the auditory (eustachian) tubes � � Protect against bacteria that may invade tissues around the openings between the nasal and oral cavities; � bacteria are trapped in tonsillar crypts and put in close contact with immune system cells

THYMUS � Location and appearance of the thymus � Primary central organ of lymphatic system � Thymus is pinkish gray in childhood; with advancing age, becomes yellowish as lymphoid tissue is replaced by fat � Structure of the thymus Pyramid-shaped lobes are subdivided into small lobules � Each lobule is composed of a dense cellular cortex and an inner, less -dense medulla � � Function � Plays of the thymus vital role in immunity mechanism � Source of lymphocytes before birth � Shortly after birth, secretes thymosin and other regulators, which enables lymphocytes to develop into T cells

SPLEEN � Location: in the left hypochondrium, directly below the diaphragm, above the left kidney and descending colon and behind the fundus of the stomach � Structure of the spleen Ovoid in shape � White pulp: dense masses of developing lymphocytes � Red pulp: near outer regions, composed of cords of white blood cells and related cells surrounded by sinusoids �

SPLEEN (cont. ) � Functions of the spleen Defense: remove microorganisms from the blood and phagocytose them � Hematopoiesis: monocytes and lymphocytes complete their development in the spleen � Red blood cell and platelet destruction: macrophages remove worn-out red blood cells and imperfect platelets and destroy them by phagocytosis; also salvage iron and globin from destroyed red blood cells � Blood reservoir: pulp of spleen and its sinuses store blood �

CYCLE OF LIFE: LYMPHATIC SYSTEM � Dramatic changes throughout life � Organs with lymphocytes appear before birth and grow until puberty � Postpuberty � Organs atrophy through late adulthood � Shrink in size � Become fatty or fibrous � Spleen: � Overall � Later develops early, remains intact function maintained until late adulthood � Deficiency permits risk of infection and cancer � Hypersensitivity: likelihood of autoimmune conditions

THE BIG PICTURE: THE LYMPHATIC SYSTEM AND THE WHOLE BODY � Lymphatic system drains away excess water from large areas � Lymph is conducted through lymphatic vessels to nodes, where contaminants are removed � Lymphatic system benefits the whole body by maintaining fluid balance and freedom from disease