Lymphatic System (NNNB1234, NNPD1032) PDF

LYMPHATIC SYSTEM NNNB1234 Anatomy & Physiology I NNPD1032 Human Anatomy DR NOR MALIA ABD WARIF Learning Objectives : To understand/identify and describe: o the components of the lymphatic system o the major trunks and ducts of the lymphatic system o the structure of the lympha...

LYMPHATIC SYSTEM NNNB1234 Anatomy & Physiology I NNPD1032 Human Anatomy DR NOR MALIA ABD WARIF Learning Objectives : To understand/identify and describe: o the components of the lymphatic system o the major trunks and ducts of the lymphatic system o the structure of the lymphatic vessels o the detailed structure of lymphoid tissues and lymph nodes  Introduction What happened during microcirculation? Blood circulates → Hydrostatic and colloid osmotic pressures at capillary beds → Force fluid out of the blood Leak out Reabsorb Fluid that remains behind in the tissue spaces, as much as 3 L daily, becomes part of the interstitial fluid These fluids will fill up the interstitial space – between cells in the surrounding tissues *glucose, amino acids, electrolytes, white blood cells  The leaked fluid and other plasma proteins escaped from the Bloodstream → MUST RETURN TO THE BLOOD → WHY? Ensures sufficient blood volume for the CVS to operate properly How do we solve this problem of circulatory The LYMPHATIC SYSTEM dynamics ?? Elaborate networks of drainage vessels that collect the excess protein- containing interstitial fluid and return it to the bloodstream The lymphatic vessels are closely associated with capillary beds →all interstitial fluid enters the lymphatic vessels → return to blood circulatory system The Lymphatic System A network of vessels, tissues and organs Functions : o Return fluids that have leaked out of blood vascular system o Site for immune surveillance (activation/proliferation of immune cells) o Production of immune cells (generative lymphoid organs) o Transporting fat to the circulatory system (mucosal associated lymphoid tissues) Component of Lymphatic System Lymphatic vessels lymph, lymph capillaries, lymphatic duct, lymphatic trunk Lymphoid organs lymph nodes, spleen thymus, bone marrow Lymphoid tissues MALT, Tonsil, NALT, BALT, GALT, Appendix, SALT  Lymph Flow Pathway Lymphatic capillaries Collecting lymphatic vessel Lymph node Lymph trunk Unidirectional Lymph duct flow Venous circulation Heart weaved between  Lymphatic Vessels Lymphatic system is not a closed system → There is no pump analogous to the heart → rely on its vessels (active skeletal muscle movement) to ensure the interstitial fluid return to circulation Larger lymphatic vessels are structurally similar to veins: Thin walled Low pressure Has valves to prevent backflow Lymphatic capillaries: Blind-ended vessels (closely associated with capillary bed) Widespread (not included bones and CNS) Remarkably permeable (like sponge) Distribution and Structure of Lymphatic Vessels A ONE-WAY system in which Capillaries weave between tissue lymph flows only toward the heart cells and blood capillaries ‘milking action’ of fluid movement valve in the vessels prevent backflow changes pressure during breathing pulsating action of arteries smooth muscle contraction of lymphatic trunk/duct skeletal muscle good physical activity for lymph flow contraction & movement  Lymphatic Capillaries Uniqueness Two unique structural modifications: Overlapping of endothelial cells forming minivalves Anchoring of endothelial cells by collagen filaments (prevent cells from collapse during pressure changes) Endothelial cells forming the capillary walls are not tightly joined→edges of adjacent cells overlap each other loosely → forming easily opened, flap-like minivalves minivalve Collagen filaments anchor the endothelial cells to surrounding structures so that any increase in interstitial fluid volume opens the minivalves, rather than causing the lymphatic capillaries to collapse Increased pressure in the interstitial space → Increased pressure within lymphatic minivalve flaps open → fluid enters capillary → minivalve flaps shut → prevent lymphatic capillary leaking out of lymph and backflow Special set of lymphatic capillary : Lacteal Transport fat from small intestine to bloodstream → large molecule cannot cross directly to blood vessels : fat absorbed by lacteal will be delivered to the blood circulation. Lymph is milky white called chyle Drains from fingerlike villi of the intestinal mucosa  Larger Lymphatic Vessels Lymphatic capillaries → First collecting vessels → Trunks → Ducts Smaller capillaries → → → → → → → → → → → larger vessels Collecting lymphatic vessels : Same three tunics as veins Thinner walls More internal valves Major trunks → Named mostly for the regions from which they drain lymph paired : lumbar (drain from lower limb) bronchomediastinal (from thorax/mediastinal) subclavian (from upper limb) jugular (head region) single : intestinal trunk (intestinal area) Lymph is eventually delivered to one of two large ducts in the thoracic region. The RIGHT LYMPHATIC DUCT → The much larger THORACIC DUCT → drains lymph from the right upper limb From the rest of the body, left side of thorax, and the right side of the head and left upper limb and left side of the thorax head. Arises anterior to the first two lumbar vertebrae as an enlarged sac, the cisterna chyli* Each terminal duct empties its lymph into the venous circulation at the junction of the internal jugular vein and subclavian vein on its own side of the body  Lymphoid Organs & Tissues Primary Bone marrow Thymus Secondary Lymph nodes Spleen Mucosa/skin -associated lymphoid tissues → Composed of reticular connective tissues  Bone Marrow Flat bones and epiphysis of long bones (adults) Hematopoiesis : birth place of all immune cells → B cells and pre-T cells Consist of : Pluripotent stem cells, lymphocytes, plasma cells, monocytes, megakaryocytes, connective tissues, stromal cells, adypocytes  Thymus Gland Bilobed Found in the inferior neck and extends into the superior thorax, where it partially overlies the heart deep to the sternum Important functions primarily during the early years of life. T lymphocyte precursors mature to become immunocompetent lymphocytes The thymus differs from other lymphoid organs in three important ways: Has no follicles because it lacks B cells Stroma of the thymus consists of epithelial cells rather than reticular fibers Only lymphoid organ that does not directly fight antigens  Lymph nodes Principal lymphoid organs in the body Nodes are clustered along the lymphatic vessels Large clusters of lymph nodes occur near the body surface where collecting vessels converge to form trunk Cervical Inguinal Axillary Basic function → protection by: Filtration Immune system activation When bacteria are recognized in the lymph fluid → more infection-fighting white blood cells are produced → lymph node swells → swelling can be felt in the neck, under the arms, and groin  Structure of Lymph node Trabeculae Most are bean shaped and less than 2.5 cm in length. Surrounded by a dense fibrous capsule Connective tissue strands called trabeculae extend inward to divide the node into a number of compartments Stroma – the internal supportive connective tissue network of reticular fibers Capsule  Structure of Lymph node Two histologically distinct regions, the cortex and the medulla. Cortex Outer cortex packed with follicles with Cortex inner germinal center -site of B-cell proliferation Medulla Deeper cortex – houses T cells in transit Medulla - medullary cords of lymphocytes, macrophages, plasma cells (activated B cells) Structure of Lymph node  Circulation in the lymph node Lymph → afferent lymphatic vessels → lymph node → subcapsular sinus → smaller sinuses in cortex → medulla → medullary sinuses → exits at hilum via efferent lymphatic vessels. Subcapsular sinus Afferent lymphatic vessels Efferent lymphatic vessels Hilum Medullary sinus  Spleen Largest lymphoid organ Left side of the abdominal Cavity just beneath the diaphragm Function of the spleen: Provides a site for lymphocyte proliferation and immune surveillance and response Blood cleansing : - Breakdown aged blood cells & platelets → stores breakdown products - Site of erythrocyte production in fetus Structure of the spleen  Lymphoid tissue – Functions include; – houses and provides a proliferation site for lymphocytes – Provides a check point for lymphocytes and macrophages. – Largely composed of a type of loose connective tissue called reticular connective tissue (except the thymus) – Macrophages live on the fibers of the reticular connective tissue network – Lymphoid tissue comes in various “packages,” such as diffuse lymphoid tissue and lymphoid follicles – Diffuse lymphoid tissue – loose arrangement of lymphoid cells and some reticular fibers – found in virtually every body organ. – Larger collections appear in the lamina propria of mucous membranes – Lymphoid follicles (lymphoid nodules) – Solid, spherical bodies → tightly packed lymphoid cells and reticular fibers – Lighter-staining germinal centers (proliferating B cells predominate) – Form part of larger lymphoid organs (e.g lymph nodes.)  Tonsils – Ring of lymphoid tissue around the entrance to the pharynx (throat) – Appear as swellings of the mucosa – Gather and remove many of the pathogens entering the pharynx in food or in inhaled air. – Named according to location. 1. Paired palatine tonsils posterior end of the oral cavity. largest tonsils and the ones most often infected. 2. Lingual tonsil base of the tongue. 3. Pharyngeal tonsil /adenoid posterior wall of the nasopharynx. 4. Tubal tonsils surround the openings of the auditory tubes into the pharynx https://images.app.goo.gl/pumpxJgT1YKP2ftE9  Peyer’s Patches – Aggregated lymphoid nodules – Large clusters of lymphoid follicles, structurally similar to the tonsils – Located in the wall of the distal portion of the small intestine https://images.app.goo.gl/7b3G1Wfg76feDxhx8  Appendix – Blind-ended tube offshoot of the first part of the large intestine – Located in the right lower quadrant of the abdomen, near the right hip bone s and – Takes up antigens from the contents of the intestine reacts to these contents https://images.app.goo.gl/osT8Uax2zUoiqwJp6