1. Chapter 20 – Lymphatic System Dr. Kim Wilson

2. Overview of the Lymphatic System Component of the circulatory system Functions: Maintains fluid balance in the internal environment and immunity Collects absorbed fat from the intestines and transport it to the systemic veins

3. Components of the Lymphatic System Lymph (lymphatic fluid) Clear, watery, moving fluid derived from blood and tissue fluid Closely resembles blood plasma in composition but has a lower percentage of protein; isotonic Lymphatic vessels (lymphatics) Return lymph to the blood Contain lymphocytes and other defensive cells Isolated structures containing lymphoid tissue: lymph nodes, aggregated lymphoid nodules, tonsils, thymus, spleen, and bone marrow (Figure 20-2) 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 Along with blood plasma, constitutes the extracellular fluid

4. The Lymphatic System and Fluid Balance Lymph transports tissue fluid, proteins, fats, and other substances to the general circulation Fluid from plasma moves into interstitial spaces (some fluid accumulates) As fluid builds up it is drained by the lymphatic vessels Lymphatic vessels begin blindly in the intercellular spaces of the soft tissues; do not form a closed circuit Lymph vessels act as drains to collect excess tissue fluid and return it to the venous blood just before it returns to the heart

5. LYMPHATIC VESSELS (LYMPHATICS) DISTRIBUTION and DRAINAGE Start as microscopic lymphatic capillaries, consisting of a single layer of flattened endothelial cells Lymphatic capillaries merge to form larger lymphatics and eventually form the main lymphatic trunks, the right lymphatic ducts, and the thoracic duct Lymph from upper right quadrant  empties into right lymphatic duct  right subclavian vein Lymph from rest of the body empties into the thoracic duct  drains into left subclavian vein Thoracic duct originates from a dilated structure known as the cisterna chyli (chyle cistern) in lumbar region of intestinal tract

6. Lymphatic Drainage in the Head and Neck

7. Structure of Lymphatic Vessels Don’t form a closed ring like blood vessels Similar to veins except for these exceptions: Have thinner walls Have more valves Contain lymph nodes Functions of the lymphatic vessels Remove high-molecular-weight substances and particulate matter from interstitial spaces Lacteals (lymphocytes in the villi of the small intestines) absorb fats and other nutrients from the small intestine

8. 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 (Figure 20-5) The lymphatic pump Lymphokinesis: the movement (flow) of lymph; can be visualized in a lymphangiogram (Figure 20-6) Lymphokinetic actions: activities that result in a central flow of lymph

11. LYMPH NODES STRUCTURE Oval, bean ‑ shaped Part of lymphatic vessels (lymph filters through each node) House lymphocytes and monocytes Trabeculae extend from the covering capsule toward the center of the node

12. LYMPH NODES (cont.) FUNCTION Nodes are a type of biological filter Once lymph enters a node, it moves slowly through sinuses to drain into the efferent exit vessel (Figure 20-10) LOCATION Most lymph nodes occur in groups Groups with greatest clinical importance are preauricular lymph nodes submental and submaxillary groups superficial cervical superficial cubital, axillary, iliac inguinal lymph nodes

13. Functions of Lymph Nodes 1.Defense How? Two mechanisms: Filtration Mechanical filtration: physically stopping particles from progressing further in the body Biological filtration: biologic activity of cells destroys and removes particles Phagocytosis Reticuloendothelial cells remove microorganisms and other injurious particles from lymph and phagocytose them (biological filtration) If overwhelmed, lymph nodes can become infected or damaged 2.Hematopoiesis Final site for maturation of some lymphocytes and monocytes

14. TONSILS Form a broken ring under the mucous membranes in the mouth and back of the throat—the pharyngeal lymphoid ring (Figure 20-17) 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 FUNCTION: 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

15. THYMUS STRUCTURE Pyramid-shaped lobes are subdivided into small lobules Each lobule is composed of a dense cellular cortex and an inner, less-dense medulla LOCATION/APPEARANCE (Figure 20-18) Primary central organ of lymphatic system Single, unpaired organ located in the mediastinum, extending upward to the lower edge of the thyroid and inferiorly as far as the fourth costal cartilage Thymus is pinkish gray in childhood; with advancing age, becomes yellowish as lymphoid tissue is replaced by fat

16. THYMUS (cont.) FUNCTIONS Plays 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 (Figure 20-19)

17. SPLEEN LOCATION Left hypochondrium, directly below the diaphragm, above the left kidney and descending colon and behind the fundus of the stomach STRUCTURE Ovoid in shape Surrounded by fibrous capsule with inward extensions that divide the organ into compartments White pulp: dense masses of developing lymphocytes Red pulp: near outer regions, composed of a network of fine reticular fibers submerged in blood that comes from nearby arterioles; composed of cords of white blood cells and related cells surrounded by sinusoids

18. Functions of the Spleen DEFENSE Filtration and phagocytosis: monocytes live in the lining of blood vessels in the spleen  carry out phagocytosis as blood passes through HEMATOPOIESIS Formation of blood cells (lymphocytes, monocytes, and platelets) RBC AND PLATELET DESTRUCTION By monocytes in blood vessels BLOOD RESERVOIR Stores large amounts of blood (350 ml) In emergency, can squeeze blood into general circulation

19. The Lymphatic Cycle Through Life 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: develops early, remains intact Overall function maintained until late adulthood Later adulthood Deficiency permits risk of infection and cancer Hypersensitivity: likelihood of autoimmune conditions

20. Summary of Main Points 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