Lesson 1 Chapter 23 – The Lymphatic System

Lesson 1 Chapter 23 – The Lymphatic System 1 Unit 9 Study Guide The lymphatic system is an integral part of the immune system and it plays an important part in the body’s defense against disease. The active part of the system is lymph fluid, which starts life as the interstitial fluid that collects between cells throughout the body. It drains into networks of tiny capillaries in tissue spaces that unite to form larger vessels called lymph vessels. Lymph nodes (lymph glands) are the filtering and storage areas of the system, and they are scattered along the routes of the lymph vessels. Unlike blood, lymph is not pumped; instead it moves passively as lymph vessels are compressed by contraction of surrounding muscles during movement. Lymph fluid enters the blood circulation via the left and right subclavian veins. Lymphoid organs, including the thymus and spleen, and lymphoid tissue, such as the tonsils and Peyer’s patches, complete the system. They contain large numbers of specialized white blood cells, particularly lymphocytes, which protect the body against non-self material such as invading microorganisms. • • Lymph consists of: • Interstitial fluid • Lymphocytes • Macrophages Lymphoid organs • • Primary lymphoid structure (thymus gland) • Causes differentiation of lymphocytes resulting in: • T cells, B cells, and NK cells Secondary lymphoid structures (lymph nodes, spleen and (lymphatic nodules)tonsils) • Consist of lymphocytes and more B cells to battle infectious agents Lymphatic System I. Lymphatic capillaries are blind-ended but highly permeable. They drain excess tissue fluid into lymph ducts. II. Lymph passes through lymph nodes and is returned by way of the lymph ducts to the venous blood. Lesson 1 Chapter 23 – The Lymphatic System Cells of the Lymphatic  Immune system composed of two types of immunity: o Innate (generally non-specific)  Barriers (physical, mechanical, biochemical)  Inflammatory response (involves a number of different WBCs and chemical mediators) o Adaptive/Acquired (specific) this is the type of immunity we talk about when we talk about lymphocytes  Macrophages and lymphocytes (lymph cells) are immune cells affiliated with the lymphatic system  They respond to: microorganisms (eg, bacteria, viruses), abnormal cells (eg, cancer) and foreign proteins (eg, toxins produced by some microorganisms) 2 Lesson 1 Chapter 23 – The Lymphatic System 3 Red bone marrow is a highly vascular tissue found in the spaces between trabeculae of spongy bone. It is mostly found in the ends of long bones and in the flat bones of the body. Red bone marrow is a hematopoietic tissue containing many stem cells that produce blood cells. All of the leukocytes, or white blood cells, of the immune system are produced by red bone marrow. Leukocytes can be further broken down into 2 groups based upon the type of stem cells that produces them: myeloid stem cells and lymphoid stem cells. Myeloid stem cells produce monocytes and the granular leukocytes—eosinophils, basophils, and neutrophils.  Monocytes. Monocytes are agranular leukocytes that can form 2 types of cells: macrophages and dendritic cells. 1. Macrophages. Monocytes respond slowly to infection and once present at the site of infection, develop into macrophages. Macrophages are phagocytes able to consume pathogens, destroyed cells, and debris by phagocytosis. As such, they have a role in both preventing infection as well as cleaning up the aftermath of an infection. 2. Dendritic cells. Monocytes also develop into dendritic cells in healthy tissues of the skin and mucous membranes. Dendritic cells are responsible for the detection of pathogenic antigens which are used to activate T cells and B cells.  Granular Leukocytes 1. Eosinophils. Eosinophils are granular leukocytes that reduce allergic inflammation and help the body fight off parasites. 2. Basophils. Basophils are granular leukocytes that trigger inflammation by releasing the chemicals heparin and histamine. Basophils are active in producing inflammation during allergic reactions and parasitic infections. 3. Neutrophils. Neutrophils are granular leukocytes that act as the first responders to the site of an infection. Neutrophils use chemotaxis to detect chemicals produced by infectious agents and quickly move to the site of infection. Once there, neutrophils ingest the pathogens via phagocytosis and release chemicals to trap and kill the pathogens. Lymphoid stem cells produce T lymphocytes and B lymphocytes.  T lymphocytes. T lymphocytes, also commonly known as T cells, are cells involved in fighting specific pathogens in the body. T cells may act as helpers of other immune cells or attack pathogens directly. After an infection, memory T cells persist in the body to provide a faster reaction to subsequent infection by pathogens expressing the same antigen. Lesson 1 Chapter 23 – The Lymphatic System 4  B lymphocytes. B lymphocytes, also commonly known as B cells, are also cells involved in fighting specific pathogens in the body. Once B cells have been activated by contact with a pathogen, they form plasma cells that produce antibodies. Antibodies then neutralize the pathogens until other immune cells can destroy them. After an infection, memory B cells persist in the body to quickly produce antibodies to subsequent infection by pathogens expressing the same antigen.  Natural killer cells. Natural killer cells, also known as NK cells, are lymphocytes that are able to respond to a wide range of pathogens and cancerous cells. NK cells travel within the blood and are found in the lymph nodes, spleen, and red bone marrow where they fight most types of infection. THE ORIGIN OF LYMPH Lymph originates as plasma (the fluid portion of blood). The arterial blood, which flows out of the heart, slows as it moves through a capillary bed. This slowing allows some plasma to leave the arterioles (small arteries) and flow into the tissues where it becomes tissue fluid. o Also known as extracellular fluid, this is fluid that flows between the cells but is not into the cells. This fluid delivers nutrients, oxygen, and hormones to the cells. Lesson 1 Chapter 23 – The Lymphatic System 5 o As this fluid leaves the cells, it takes with it cellular waste products and protein cells. o Approximately 90% of this tissue fluid flows into the small veins. Here it enters the venous circulation as plasma and continues in the circulatory system. o The remaining 10% of the fluid that is left behind is known as lymph. LYMPHATIC CAPILLARIES In order to leave the tissues, the lymph must enter the lymphatic system through specialized lymphatic capillaries. Approximately 70% of these are superficial capillaries located near, or just under, the skin. The remaining 30%, which are known as deep lymphatic capillaries, surround most of the body’s organs. Lymphatic capillaries begin as blind-ended tubes that are only a single cell in thickness. These cells are arranged in a slightly overlapping pattern, much like the shingles on a roof. Each of these individual cells is fastened to nearby tissues by an anchoring filament. LYMPHATIC VESSELS The lymphatic capillaries gradually join together to form a mesh-like network of tubes that are located deeper in the body. o As they become larger, and deeper, these structures become lymphatic vessels. o Deeper within the body the lymphatic vessels become progressively larger and are located near major blood veins. o Like veins, the lymphatic vessels, which are known as lymphangions, have one-way valves to prevent any backward flow. o Smooth muscles in the walls of the lymphatic vessels cause the angions to contract sequentially to aid the flow of lymph upward toward the thoracic region. Because of their shape, these vessels are previously referred to as a string of pearls. Lymph Nodes There are between 600700 lymph nodes present in the average human body. It is the role of these nodes to filter the lymph before it can be returned to the circulatory system. Although these nodes can increase or Lesson 1 Chapter 23 – The Lymphatic System 6 decrease in size throughout life, any nodes that has been damaged or destroyed, does not regenerate. o Afferent lymphatic vessels carry unfiltered lymph into the node. Here waste products, and some of the fluid, are filtered out. o In another section of the node, lymphocytes, which are specialized white blood cells, kill any pathogens that may be present. This causes the swelling commonly known as swollen glands. o Lymph nodes also trap and destroy cancer cells to slow the spread of the cancer until they are overwhelmed by it. o Efferent lymphatic vessels carry the filtered lymph out of the node so that it can continue its return to the circulatory system. Lymphatic Ducts All of the lymphatic vessels of the body carry lymph toward the 2 lymphatic ducts: the thoracic Lesson 1 Chapter 23 – The Lymphatic System 7 duct and the right lymphatic ducts. These ducts serve to return lymph back to the venous blood supply so that it can be circulated as plasma. o Thoracic duct. The thoracic duct connects the lymphatic vessels of the legs, abdomen, left arm, and the left side of the head, neck, and thorax to the left brachiocephalic vein. (largest) o Right lymphatic duct. The right lymphatic duct connects the lymphatic vessels of the right arm and the right side of the head, neck, and thorax to the right brachiocephalic vein. (smaller) Lesson 1 Chapter 23 – The Lymphatic System 8 Lesson 1 Chapter 23 – The Lymphatic System 9 Distribution Lymph capillaries → lymph collecting vessels → lymph trunks → lymph ducts → subclavian vein In summary: 1. Capillaries One-way system flowing to heart, weaves between tissue cells and blood capillaries of almost all organs (except CNS, bone, and teeth) o Lymph capillaries have permeability due to unique structure:  Endothelial cells forming walls of lymphatic capillaries are not joined but yet overlap, forming mini valves  Bundles of filaments anchor endothelial cells to surrounding structures so that any increase in interstitial fluid volume separates the cell flaps, exposing gaps in the wall, rather than causing the lymphatic capillary to collapse; therefore is a one- way swinging door providing sufficient blood volume to operate CVS o Specialized lymph capillaries in intestinal mucosa (lacteals) 2. Lymphatic collecting vessels o Lymph flowing from capillaries enter lymph collecting vessels o Have the same three tunics as veins, but are thinner walled, have more internal valves, and anastomose more o Receive nutrient blood supply from a branching vasa vasorum 3. Lymphatic trunks o Formed by the union of the largest collecting vessels o Named mostly for the regions from which they collect lymph o Lumbar, bronchomediastinal, subclavian, jugular and intestinal 4. Lymphatic ducts Lymph is delivered to one of two large ducts o Right lymphatic duct drains lymph from the right upper arm and the right side of the head and thorax o Thoracic duct receives lymph from the rest of the body Lesson 1 Chapter 23 – The Lymphatic System 10 o Intestinal trunk and lumbar trunks merge to form the cisterna chyli of the thoracic trunk o Lymph empties into venous circulation at or near the junction of internal jugular vein and subclavian vein Lymphoid Organs • • • Primary lymphatic organs • provide environment for stem cells to divide & mature into B and T lymphocytes • Thymus and bone marrow Secondary lymphatic organs and tissues • site where most immune responses occur • lymph nodes, spleen & lymphatic nodules Spleen. The spleen is a flattened, oval-shaped organ located in the upper left quadrant of the abdomen lateral to the stomach. The spleen is made up of a dense fibrous connective tissue capsule filled with regions known as red and white pulp. Red pulp, which makes up most of the spleen’s mass, is so named because it contains many sinuses that filter the blood. Red pulp contains reticular tissues whose fibers filter worn out or damaged red blood cells from the blood. Macrophages in the red pulp digest and recycle the hemoglobin of the captured red blood cells. The red pulp also stores many platelets to be released in response to blood loss. White pulp is found within the red pulp surrounding the arterioles of the spleen. It is made of lymphatic tissue and contains many T cells, B cells, and macrophages to fight off infections. Red pulp = occupied by the dead RBC White pulp = consists of lymphocytes Lesson 1 Chapter 23 – The Lymphatic System 11 • Thymus. The thymus is a small, triangular organ found just posterior to the sternum and anterior to the heart. The thymus is mostly made of glandular epithelium and hematopoietic connective tissues. The thymus produces and trains T cells during fetal development and childhood. T cells formed in the thymus and red bone marrow mature, develop, and reproduce in the thymus throughout childhood. The vast majority of T cells do not survive their training in the thymus and are destroyed by macrophages. The surviving T cells spread throughout the body to the other lymphatic tissues to fight infections. By the time a person reaches puberty, the immune system is mature and the role of the thymus is diminished. After puberty, the inactive thymus is slowly replaced by adipose tissue. • Secrete “thymosin” for T cell maturation [Distribution of Lymph Nodes] Lesson 1 Chapter 23 – The Lymphatic System 12 Lesson 1 Chapter 23 – The Lymphatic System Tonsils. There are 5 tonsils in the body—2 lingual, 2 palatine, and 1 pharyngeal. The lingual tonsils are located at the posterior root of the tongue near the pharynx. The palatine tonsils are in the posterior region of the mouth near the pharynx. The pharyngeal pharynx, also known as the adenoid, is found in the nasopharynx at the posterior end of the nasal cavity. The tonsils contain many T and B cells to protect the body from inhaled or ingested substances. The tonsils often become inflamed in response to an infection. 13 Lesson 1 Chapter 23 – The Lymphatic System 14 Lymphoid Organs In Summary A. Spleen     Blood-rich, size of fist, left side of abdominal cavity beneath diaphragm Site of lymphocyte proliferation and immune response Three functions:  Stores some products of RBC degradation  Site of erythrocyte production in fetus  Stores thrombocytes Sturcture:  Fibrous capsule  Trabeculae  Red pulp (RBCs and macrophage)  White pulp (lymphocytes) B. Thymus     Located in the lower neck extending into mediastinum of thorax Secretes hormones (thymosins) that stimulate the development and cell differentiation of T lymphocytes T cells become immunocompetent in infants (increases immune responses) Atrophies after adolescence C. Tonsils    Ring of lymph tissue around entrance of pharynx Gather and remove many pathogens entering the pharynx Types: palatine, lingual, pharyngeal, and tubal tonsils D. Peyer's patches   Located in the wall of the distal portion (ileum) of small intestine Contains macrophages that capture and destroy bacteria thereby preventing microbes from breaching the intestinal wall