Chapter 14 Lecture Outline See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education. 14.1: Introduction to the Lymphatic System & Immunity Lymphatic System: • Group of cells and chemicals that travel in lymphatic vessels, and organs & glands that synthesize them • The lymphatic system contains a network of vessels that assists in the circulation of body fluids • Lymphatic vessels collect and carry away excess fluid from interstitial spaces, eventually returning it to the blood • Special vessels called lacteals transport absorbed fats to the circulation • The organs, cells, and biochemicals of the lymphatic system help defend body against disease ©McGraw-Hill Education. 14.2: Lymphatic Pathways • Lymphatic pathways start as lymphatic capillaries, that merge to form larger vessels, that empty into veins in the thoracic cavity • Lymphatic Capillaries: • Lymphatic capillaries are tiny, closed-ended tubes that extend into interstitial spaces, paralleling the blood capillaries • Found all over body, except in central nervous system • They receive tissue (interstitial) fluid through their thin walls and slits between cells • Once inside a lymphatic capillary, tissue fluid is called lymph ©McGraw-Hill Education. Lymphocyte Lymphocyte Nucleus of lymphocyte Erythrocytes Lymphatic Capillaries ©McGraw-Hill Education. Lymphatic Vessels • The walls of lymphatic vessels are thinner than those of veins, but are constructed with the same 3 layers • They also have flaplike valves on the inside, like veins • Larger lymphatic vessels pass through organs called lymph nodes, and then merge to form larger lymphatic trunks ©McGraw-Hill Education. Lymphatic Capillaries Transport Excess Fluid Back to the Blood ©McGraw-Hill Education. Valve in a Lymphatic Vessel Insert Figure 14.3 here ©McGraw-Hill Education. Lymphatic Trunks and Collecting Ducts • The lymphatic trunks drain lymph from the lymphatic vessels • The trunks are named for the regions they drain • These trunks empty into 1 of 2 collecting ducts, either the thoracic duct or right lymphatic duct • The right lymphatic duct drains the right side of the head and neck, the right arm, and right thorax, and empties into the right subclavian vein • The thoracic duct, the larger of the collecting ducts, drains the rest (majority) of the body, and empties into the left subclavian vein ©McGraw-Hill Education. Cysterna Chyli Thoracic Duct Lymphatic Pathways ©McGraw-Hill Education. Lymphatic Drainage of Mammary and Axillary Regions Axillary lymph nodes Pectoralis major muscle 21-13 14.3: Tissue Fluid and Lymph • Lymph is tissue fluid that has entered a lymphatic capillary; lymph formation depends on tissue fluid formation • Tissue Fluid Formation: • Tissue fluid is made up of water and dissolved substances that leave blood capillaries by filtration and diffusion • Tissue fluid is almost the same as blood plasma, except that it does not contain large plasma proteins; they are too large to pass through capillary walls • Plasma proteins create plasma colloid osmotic pressure, that draws most of the fluid back into the capillaries • Fluid that does not return to the capillaries becomes tissue fluid ©McGraw-Hill Education. Lymph Formation and Function • Filtration from the plasma usually occurs to a greater extent than reabsorption; this leads to tissue fluid formation • Rising osmotic pressure in the tissues interferes with the return of fluids to the bloodstream • Increasing tissue fluid hydrostatic pressure forces some of the fluid into lymphatic capillaries, where it is now called lymph • Most substances, including small proteins, are returned to blood via the lymph • Lymph also transports foreign particles, including bacteria and viruses, to the lymph nodes for recognition and destruction ©McGraw-Hill Education. 14.4: Lymph Movement • The hydrostatic pressure of tissue fluid drives the entry of fluid into lymphatic capillaries, where it is now called lymph • Forces that move blood in veins, such as skeletal muscle contraction, breathing movements, contraction of smooth muscle in the walls of the vessels (lymphatic trunks, in this case), and the presence of valves, are also the forces that propel lymph through lymphatic vessels • A condition that interferes with the flow in lymph will result in an accumulation of lymph in the interstitial spaces, called edema • During surgery, lymphatic vessels or tissues may be removed or disturbed, resulting in edema ©McGraw-Hill Education. Lymphatic Drainage of the Breast ©McGraw-Hill Education. 14.5: Lymphatic Tissues and Organs • Lymphatic tissue contains lymphocytes, macrophages, and other cells • Diffuse, unencapsulated lymphatic tissue associated with the digestive, respiratory, urinary, and reproductive systems is called mucosa-associated lymphoid tissue (MALT) • Tonsils, appendix, and Peyer’s patches are compact masses of lymphatic nodules • Encapsulated lymphatic organs include lymph nodes, the thymus, and spleen ©McGraw-Hill Education. Lymph Nodes • Lymph nodes, which contain lymphocytes and macrophages, are located in groups or chains along lymphatic vessels • Structure of a Lymph node: • Lymph nodes are bean-shaped • Blood vessels, nerves, and efferent lymphatic vessels enter or exit at the indented hilum • Afferent lymphatic vessels enter on the convex surface • Lymph nodes are covered with a connective tissue capsule, that extends inside the node and divides it into nodules and spaces called sinuses • Lymph nodes contain both lymphocytes and macrophages; they filter the lymph as it flows through them, removing many pathogens ©McGraw-Hill Education. Lymph Node Histology Cortex Medulla Lymphadenopathy Lymphadenitis Germinal centers Lymph Node: LM Low MagnificationSecondary Lymph node Cortex Germinal center Primary nodules nodules Capsule Subcapsular sinus Medulla Medullary cords Medullary sinus Lymph Node: LM Medium Magnification Subcapsular Primary Capsule sinus Cortex Medulla nodules Trabecula Cortical Secondary Medullary Medullary Germinal sinus nodule cords sinus centers Lymph Node (Lymphoid Nodule) LM: Medium Magnification Capsule Subcapsular sinus Reticular fibers Germinal center of Mantle zone of lymphatic nodule lymphatic nodule Lymph Node (Lymphoid Nodule) LM: High Magnification Lymphoid nodule in lymph B lymphocytes in lymphoid node nodule Germinal center of lymphoid Mantle zone of lymphoid nodule nodule Lymph Node (Medullary Sinus) SEM: Medium Magnification Reticular fibers of lymph Lymphocytes node Tonsils Palatine Pharyngeal Lingual 21-26 Palatine Tonsil Histology Epithelium Germinal centers Tonsil Lymphatic nodules Tonsillar crypts Peyer Patches 21-28 A Section Through a Lymph Node ©McGraw-Hill Education. A Lymph Node with Lymphatic Vessels ©McGraw-Hill Education. Locations of Lymph Nodes • The lymph nodes generally occur in chains along the parts of the larger lymphatic vessels • Lymph nodes are not found in the central nervous system • Major areas of concentrations of lymph nodes: cervical, thoracic, axillary, supratrochlear, abdominal, pelvic, and inguinal regions ©McGraw-Hill Education. Mediastinal nodes Lymph Nodes Axillary nodes Inguinal nodes Iliac nodes Pelvis Lymphangiogram: A – P View Iliac lymph nodes Pelvic inlet Inguinal lymph nodes Pubic symphysis Locations of Major Lymph Nodes ©McGraw-Hill Education. Functions of Lymph Nodes Main functions of lymph nodes: • Filter lymph and remove bacteria and cellular debris before lymph is returned to the blood • Immune surveillance: Monitor body fluids; performed by lymphocytes and macrophages • Lymph nodes are also centers of lymphocyte production • Lymphocytes attack viruses, bacteria and parasitic cells that enter a lymph node • Macrophages engulf and destroy foreign particles, debris, and damaged cells ©McGraw-Hill Education. Thymus • The thymus is a soft, bi-lobed organ located behind the sternum, above the heart • It shrinks in size during the lifetime; large in children, small in adults, replaced by adipose & connective tissue in the elderly • The thymus is surrounded by a connective tissue capsule that extends inside it and divides it into lobules • Lobules contain lymphocytes, some of which mature into T cells or T lymphocytes, that leave the thymus to provide immunity • The thymus secretes hormones called thymosins, which influence the maturation of T lymphocytes ©McGraw-Hill Education. The Location of the Thymus ©McGraw-Hill Education. Thymus Thymus Gland Thymus (adult) Thymus (infant) Fetal Thymus Lobule of thymus LM: Low Magnification Cortex of thymus Lobe of thymus Medulla of thymus Septa of thymus Thymus (Hassell’s Corpuscles) LM: High Magnification Hassall’s corpuscle Blood vessels in medulla of thymus A Section Through the Thymus ©McGraw-Hill Education. Spleen • The spleen lies in the upper left abdominal cavity • Spleen is the body’s largest lymphatic organ • The spleen resembles a large lymph node except that it contains blood instead of lymph • Composed of white pulp, which contains many lymphocytes, and red pulp, which contains red blood cells, macrophages, and lymphocytes • The spleen filters the blood and removes damaged blood cells and bacteria ©McGraw-Hill Education. Spleen 21-44 Histology of the Spleen Red pulp White pulp Capsule Spleen LM: Medium Magnification Central white pulp arteries Red pulp Germinal center