The Lymphatic System PDF

The Lymphatic System Dr. Elita Partosoedarso You can resize the slide images, delete the ones that you don’t need and generally reorganize them to suit your needs. Remember that all GoogleSlides and GoogleDocs in this course have been set as “View Only” so you have...

The Lymphatic System Dr. Elita Partosoedarso You can resize the slide images, delete the ones that you don’t need and generally reorganize them to suit your needs. Remember that all GoogleSlides and GoogleDocs in this course have been set as “View Only” so you have to sign in with any Google account, go to “File” at the top left corner, and select “Download” or “Make a copy” to make your own notes. ○ Do NOT select “Request Edit Access” as you will not get a response. Treat the recording similar to an in-person lecture, ie watch the recording without pausing and rewinding to capture every single word: a 40 minute recording should take you 40 minutes to go through, not 4 hours.  Lymphatic system overview Connection between immune system and lymphatic system How connected are they? Can one function without the other? Functions of the lymphatic system Return of excess interstitial fluid Flow of lymphatic fluid Lymphokinesis Lymphoid Organs and Lymphocyte Development Primary lymphoid organs: Red bone marrow and thymus gland Secondary lymphoid organs: lymph nodes, spleen, tonsils  The lymphatic and immune systems are interconnected to each Anatomy of the Lymphatic other such that the two systems are virtually indistinguishable. Overview and Immune Systems 1. Immune system: complex group of cells & organs that destroys/neutralizes pathogens that may cause disease or death 2. Lymphatic system: system of vessels (lymphatics), cells & organs that delivers lymph to the general circulation excess fluids to blood, filters pathogens from blood. ○ Lymph: moving fluid derived from the blood and tissue fluid 3 Functions of the Lymphatic System 1. return body fluids to the bloodstream. ○ Out of the 20 L/day of plasma filtered into interstitial space, 17L is reabsorbed back into capillaries and 3L returns as lymph via lymphatic system. 2. transports dietary lipids, large proteins and fat-soluble vitamins absorbed from the gut. 3. Transports cells of the immune system 4. Contains lymph nodes which function as major staging areas for the development of critical immune responses 4 Flow of the Lymphatic System Excess interstitial fluid enters lymphatic capillaries Fluid is collected into increasingly larger lymphatic vessels Travels through 500-600 lymph nodes (groin, armpits, neck, chest, abdomen) Fluid empties into bloodstream by a series of lymphatic ducts at the jugular and subclavian veins Interstitial fluid becomes become lymph fluid when it enters the lymphatic system Similarities between lymph and interstitial fluid (IF): both are clear watery extracellular fluid (ECF) which resemble blood plasma in composition Differences: Lymph is found in lymphatic vessels and contains higher protein level from protein-rich lymph from gut while interstitial fluid (IF) fills spaces between cells with lower protein levels than lymph 5  Lymphatic Capillaries (terminal lymphatics) Location: interlaced among blood capillaries, arterioles and venules Characteristics blind ending (closed at one end) with overlapping cells to allow interstitial fluid to flow into them one cell-thick layer of endothelial cells with spaces between endothelial flaps and collagen fibers Collagen anchor cells to surrounding structures and help keep flaps open during high interstitial pressure flaps close to prevent “backflow” during low interstitial pressure and open during high interstitial pressure to allow fluid to enter. contains one-way valves (backflow prevention valves) keep lymph moving toward heart Fluid is forced into the lymphatic capillaries by body movements, skeletal muscle contraction, and breathing, similar to movement of venous blood In the small intestine, lacteals transport dietary lipids and lipid-soluble vitamins as a milky fluid (chyle) to the bloodstream. 6  Lymphatic Drainage Lymphatic and blood capillary networks ○ lie side by side but are always independent of each other ○ act as “drains” to collect and return excess tissue fluid to the venous blood ○ Increased interstitial fluid would cause massive edema (swelling) of tissue Lymphatic networks ○ located in interstitial spaces and are widely distributed throughout ○ main lymphatic trunks: right lymphatic duct and thoracic duct. ○ lymphatic fluid is returned to systemic blood just before entering the heart Overall drainage system of the body is asymmetrical ○ Lymph from the upper right quadrant (purple) empties into the right lymphatic duct and then the right subclavian vein ○ Lymph from the rest of the body (yellow) drains into the thoracic duct which empties into the left subclavian vein. 7  Lymphokinesis 1. Lymphokinesis: movement of lymph towards the heart with the help of valves and two pumps Pressure in the lymphatic system is very low: lymph moves quite slowly compared to circulation of blood. Fluid continually enters the blood and lymphatic circulation systems from the interstitial fluid. System of valves (similar to valves in veins) support movement of lymph towards the heart 2. Lymph entrance and return rates vary, depending on generalized physical activity changes in interstitial fluid pressure rate and depth of respiration arterial pulsations and postural changes passive compression (massage) of the body’s soft tissues 8  The lymphatic pumps LMC lymphatic muscle cells contraction The same two pumps that help with the movement of venous blood towards the heart also help to propel lymph towards the heart (lymphokinesis) Respiratory Pump 1. During inspiration, diaphragm contracts and moves downward, increasing volume of thorax and decreasing thoracic pressure, pulling lymph towards the heart 2. During expiration, diaphragm relaxes and moves upward, decreasing volume of thorax and increasing thoracic pressure, pushing lymph into the heart Skeletal Muscle Pump Skeletal muscle contraction causes a local area of high blood pressure and opening the valve to allow lymph flow to the next compartment (towards the heart) When pressure below the valve drops, lymph begins to flow backward but fills the “pockets” formed by the valve flaps, pushing the flaps together and thus blocking further backward flow. 9 Lymphocyte Development Lymphoid Organs and Lymphocytes include B cells, T cells, plasma cells, and natural killer cells Lymphoid organs : location of maturation, proliferation and selection of lymphocytes 1. Primary lymphoid organs ○ Red bone marrow and thymus gland: B cells develop mainly in bone marrow while immature T cells (thymocytes) will mature in thymus gland ○ location where lymphocytes develop and mature 2. Secondary lymphoid organs: ○ Includes lymph nodes, spleen, tonsils 10 ○ Location where lymphocytes mount their immune responses from  Thymus 1. Primary lymphoid organ located between sternum and aorta Connective tissue holds lobes closely together while divides thymus into lobules via trabeculae which separates lobes and forms a capsule Divided into inner and outer regions - Outer cortex is densely packed with mostly thymocytes and phagocytes (macrophages, dendritic cells) - Inner medulla is not as densely packed and is point of departure for thymocytes to leave thymus 11 Tonsils: Secondary lymphoid organs 1. Structure: Lymphoid nodules containing dense cluster of lymphocytes with no fibrous capsule 2. Location: along pharynx to encounter environmental pathogens from respiratory and digestive tracts 3. Function: develop immunity to common environmental pathogens that are eaten or inhaled so that they will be protected in their later lives 4. Pharyngeal tonsil (adenoid) swells in response to an infection 5. Location is important because pathogens that enter via the respiratory and digestive tracts can penetrate tonsillar tissues to be eliminated by lymphoid follicles 6. Children with recurring throat infections, involving palatine tonsils, may result in swelling that interfere with breathing and/or swallowing. 12 Lymph Nodes: Secondary lymphoid organ Function: mechanical and biological filtration of debris and pathogens from the lymph. Lymph nodes can swell if the phagocytes are overwhelmed by the number of microorganisms entering the nodes Location: along the paths of collecting lymphatic vessels. Structure: outer cortex composed of packed lymphocytes that surround a less dense area (germinal center). Enclosed by a fibrous capsule Structure 1. Lymphoid follicles: contain germinal centers, with specific B cell-rich and T cell-rich areas 2. Germinal centers: sites of rapidly dividing and differentiating B lymphocytes 3. Dendritic cells and fixed macrophages: line the sinuses between afferent and efferent vessels: internalize and kill most pathogens that enter interstitial fluid 4. Afferent lymphatic vessels: major routes into the lymph node 13 5. Efferent lymphatic vessels: major routes out of the lymph node  Spleen: Secondary lymphoid organ Structure: fragile organ without a strong capsule. Dark red due to its extensive vascularization Function: “filter of blood” as well as a reservoir of blood 1. White pulp: surrounds a central arteriole ○ Site where adaptive T and B cell responses are mounted ○ Contains germinal centers of dividing B cells surrounded by T cells and accessory cells 2. Red pulp: network of fine reticular fibers ○ filtration system of the blood ○ contains fixed macrophages and dendritic cells that remove microbes and other materials from the blood, including dying red blood cells and platelets 14  The Mucosal Immune Response Mucosal tissues are major barriers to pathogens entering the body Mucosa-associated lymphoid tissue (MALT) found in mucosa of gastrointestinal tract, breast tissue, lungs, and eyes, with Peyer’s patches found in small intestine Bronchus-associated lymphoid tissue (BALT) found along bifurcations of the bronchi, and between bronchi and arteries. Together with tonsils, are effective against inhaled pathogens. Neutralizing antibodies: basis for vaccines, eg flu vaccine enhances IgA production. IgA antibodies in mucus secretions bind to the pathogen Pathogen is coated with antibodies (neutralization) Pathogen cannot bind to receptors on cells Pathogen cannot enter cells 15 Body is protected