The Lymphatic System - PN Anatomy Module (PDF)

The Lymphatic System PN Structure and Function of the Human Body Week 8 Lymphatic System Overview: Network of vessels that collect lymph (fluid) from body tissues and return it to the bloodstream and brings in immune cells to tissues where needed. It also transports diet...

The Lymphatic System PN Structure and Function of the Human Body Week 8 Lymphatic System Overview: Network of vessels that collect lymph (fluid) from body tissues and return it to the bloodstream and brings in immune cells to tissues where needed. It also transports dietary fats and immune cells throughout the body.  Functions of the Lymphatic System Fluid Regulation: The lymphatic system drains excess fluids, preventing the accumulation of interstitial fluid between tissues. It returns this fluid to the bloodstream through a network of vessels, trunks, and ducts. Lymph Formation: Interstitial fluid is termed lymph once it enters the lymphatic system. Around 3 liters of the 20 liters of plasma that leak into tissue spaces daily are managed by the lymphatic system, preventing the buildup of interstitial fluid. Lymphatic System and Health: Damage to the lymphatic system, caused by factors like cancer cells or injury, can result in the accumulation of protein-rich interstitial fluid, a condition known as lymphedema, which can have serious health consequences.  https://www.youtube.com/watch?v=5YPM74FZDQQ Anatomy of the Lymphatic System Primary Lymphoid Organs Bone Marrow: Site of immune cell production and maturation of B-cells. Hematopoiesis is the process of blood cell formation. Thymus: site of T-cell maturation What organ of the lymphatic system is the site of T-cell Maturation? a. Lymph nodes b. Spleen c. Cisterna chyli d. Thymus What is Hematopoeisis? What are the roles of the Lymphatic system? Secondary Lymphoid Organs Lymph nodes Lymphatic vessels Spleen Tonsils Lymph Nodes Role of Lymph Nodes: Lymph nodes, small bean-shaped organs in the lymphatic system Act as crucial sites for immune cells to develop important immune responses. Serve as major staging areas for the maturation and coordination of these responses. Lymph Node Locations: Commonly found in various regions: near the groin, armpits, neck, chest, and abdomen. Approximately 500–600 lymph nodes are present throughout the human body. Lymph Nodes as a secondary lymphoid Organ Function: Act as filters for lymph, removing debris and pathogens. Pathogen Removal: Bacteria entering the lymph are captured in lymphatic capillaries and transported to regional lymph nodes. Pathogen Destruction: Dendritic cells and macrophages inside the nodes eliminate and kill many pathogens. Role in Immune Responses: Site for adaptive immune responses involving T cells, B cells, and related cells. Structure: Enclosed by tough connective tissue capsules, divided by trabeculae, with structural support provided by reticular fibers.  Lymph Nodes Lymph Node Pathways Afferent Lymphatic Vessels: Major entry routes into the lymph node. Efferent Lymphatic Vessels: Pathways for cells and lymph fluid leaving the node. Internal Structure of Lymph Node: Subcapsular Sinus: Entry point for lymph, occupied by dendritic cells, macrophages, and reticular fibers. Cortex: Contains lymphoid follicles with germinal centers of rapidly dividing B cells, surrounded by T cells and other accessory cells. Medulla: Consists of medullary cords filled with B cells and plasma cells, and medullary sinuses where lymph gathers before exiting via efferent vessels.  Lymphatic System vs. Cardiovascular System Pumping Mechanism: Lymph is not actively pumped by the heart, unlike blood in the cardiovascular system. Movement of Lymph: Lymph is propelled through the vessels by the body's movements, such as skeletal muscle contractions during physical activity and breathing. Valves in Lymphatic Vessels: One-way valves, known as semi- lunar valves, help maintain the flow of lymph towards the heart. Path of Lymph Flow: Starts from lymphatic capillaries. Progresses through lymphatic vessels. Drains into the circulatory system via the lymphatic ducts situated at the juncture of the jugular and subclavian veins in the neck.  https://www.youtube.com/watch?v=cCPyWFK0IKs Lymphatic vessels Lymphatic Vessel Structure: Begins as open-ended capillaries. Progresses into larger lymphatic vessels. Eventually connects to the bloodstream through a series of ducts.  Lymph Capillaries Lymphatic Capillaries (Terminal Lymphatics): Function: Serve as the entry points for interstitial fluid to enter the lymphatic system and transform into lymph fluid. Distribution: Found in nearly all body tissues, interwoven among the arterioles and venules of the circulatory system in the soft connective tissues. Exceptional Absence: Lymphatic capillaries are absent in specific areas of the body, including the central nervous system, bone marrow, bones, teeth, and the cornea of the eye. These areas lack lymphatic vessels.  Lymphatic Capillaries (continued) Structure of Lymphatic Capillaries Composed of a single layer of endothelial cells, forming an open- ended system. Fluid Entry Mechanism: These vessels allow interstitial fluid to flow into them through overlapping cells. Endothelial Flaps' Function: When interstitial pressure is low, these flaps close, preventing fluid backflow. As pressure increases, spaces between cells open to permit fluid entry. Role of Collagen Filaments: Collagen filaments, anchoring capillaries to surrounding structures, facilitate fluid entry by pulling on endothelial cell flaps as interstitial pressure rises. Role of Lymphatic Capillaries in the Small Intestine: Lacteals in the Small Intestine: Specialized lymphatic capillaries known as lacteals are crucial. Function of Lacteals: Responsible for transporting dietary lipids and lipid-soluble vitamins to the bloodstream. Formation of Chyle: In the small intestine, dietary triglycerides and other lipids combine with proteins, forming a milky fluid called chyle. This chyle is then carried through the lymphatic system, eventually entering the liver and bloodstream. Peyer’s Patches are found in the ileum. Peyer's patches keep the intestinal flora at appropriate levels and the pathogens at bay, thereby preventing a large number of infections.  What is the role of Peyer’s patches? A-keep the intestinal flora at appropriate levels and the pathogens at bay, thereby preventing a large number of infections. Where are Peyer’s patch present? A- Ileum B- Stomach C- Large Intestine D- Bone Lymphatic Vessels and Valves Lymphatic Vessels and Valves: Three-tunic structure similar to veins. One-way valves are closely spaced, causing bulges, giving vessels a beaded appearance. Formation of Lymphatic Trunks: Superficial and deep lymphatics merge into larger vessels called lymphatic trunks. Lymphatic Vessels and Valves Drainage Pathways: Right side (head, thorax, right upper limb) drains into the right subclavian vein via the right lymphatic duct. Remaining body areas drain into the larger thoracic duct on the left side, which empties into the left subclavian vein. Origin of Thoracic Duct: Begins beneath the diaphragm in the cisterna chyli, receiving lymph from lower abdomen, pelvis, and lower limbs via left and right lumbar trunks and the intestinal trunk.  The Spleen as a Secondary Lymphoid Organ Size and Position: Approximately 12 cm (5 in) long, attached to the stomach's lateral border via the gastrosplenic ligament. Fragile Structure: Lacks a strong capsule and has a dark red appearance due to extensive vascularization. Functions of the Spleen: "Filter of the Blood": Extensive vascularization and presence of macrophages and dendritic cells filter microbes and waste from the blood, including the removal of dying red blood cells. Immune Responses: Acts as a site for immune responses against pathogens present in the blood.  Tonsils Tonsils - Specific Lymphoid Nodules: Locations and Importance: Located along the inner surface of the throat; important for developing immunity to oral pathogens. Types of Tonsils: Pharyngeal tonsil and palatine tonsils. Histological Features: Lack a complete capsule, contain deep invaginations (tonsillar crypts) in the epithelial layer, allowing pathogens to penetrate deeper, where they're acted upon and eliminated by lymphoid structures. Function: Help in recognizing, fighting, and developing immunity against common environmental pathogens, particularly in children. Tonsil Removal: Indications for Removal: Recurring throat infections, especially when swelling of the  Lymphatic System VS. Immune System The immune system defends against harmful pathogens, while the lymphatic system is closely associated with the immune system, working together to filter pathogens and manage excess fluids in the body.  Antigens Antigens: Large, complex components on pathogens with multiple antigenic determinants. Determinants are small regions where receptors bind. Composition of Determinants: Protein antigens have ≤6 amino acid residues; carbohydrate antigens contain 1-2 sugar moieties. Carbohydrate antigens are less diverse than protein antigens. Locations and Importance: Carbohydrate antigens found on bacterial cell walls and ABO blood group antigens on red blood cells. Protein antigens crucial for immune responses to viruses and parasites. Specificity Basis: Specific immune response relies on the interaction between antigen shape and the complementary antigen-binding site formed by amino acids.  https://www.youtube.com/watch?v=UZTf3OXJDWA Immune Cell Origins: Cells of the immune system originate from the bone marrow within the hematopoietic system. Lymphocytes of the adaptive immune system mature in primary lymphoid organs like the bone marrow and thymus gland. Primary and Secondary Organs: Primary organs (bone marrow, thymus) are where lymphocytes mature and gain infection-fighting abilities. Secondary organs are sites where mature immune cells gather to respond to invading pathogens. Phases of Immune Function Phases of Immune Function: Barrier Defenses: Immediate protection by the skin and mucous membranes to prevent invasion by pathogens. Innate Immune Response: Rapid but non-specific defense involving specialized cells and soluble factors. Adaptive Immune Response: Slower but specific and powerful defense controlled primarily by lymphocytes, offering more targeted immune reactions. Blood Cell Origins: All immune-related blood cells originate in the bone marrow from hematopoietic stem cells. Hematopoietic stem cells continuously differentiate into various blood cells to replace aging or non-functioning cells. Barrier Defences (1rst line) Physical Barriers: First Line of Defense: Physical barriers are the first line of defense against pathogens. Continuous Protection: They work all the time, not just when there's an infection. External Surfaces: Found on the outside of the body where germs might try to enter. Skin: Main Barrier: The skin is the primary barrier to keep germs out. Protective Features: It has a dry, outer layer of dead cells that's not suitable for germ growth. As these cells shed, they take germs with them. Sweat and Secretions: Sweat and other skin secretions help by maintaining an unfavorable pH, containing substances harmful to germs, and physically washing away microbes. Barrier Defences (continued) Saliva in the Mouth: Lysozyme Power: Contains lysozyme enzyme that breaks down bacteria by eating their cell walls. Stomach Acids: Deadly to Pathogens: Strong acidic stomach environment is fatal to many germs. Mucus in Different Areas: Locations: Found in gastrointestinal, respiratory, reproductive tracts, as well as eyes, ears, and nose. Catches and Removes: Traps germs and dirt, helping to get rid of them. Respiratory Tract: Ciliated cells move mucus upwards to the mouth where it's swallowed and faces the stomach's strong acids. Reason for Multiple Barriers: Breathing vs. Other Activities: Breathing happens more often than eating or other activities that expose us to germs, so these extra barriers protect these important areas. Immune System – Two Mechanisms Innate Immune Response (2nd line of defense): Speed: Quick but not very specific. Effectiveness: Sometimes not fully effective. How it works: Acts rapidly against a range of pathogens without specific targeting. Slows pathogen growth, buying time for the adaptive immune system to strengthen. Provides initial defense against a wide range of pathogens. Cells of the Innate immune response: Neutrophils, Monocytes, Macrophages, dendritic cells, Natural Killer cells, basophils, eosinophils. https://www.youtube.com/watch?v=yjAZXlMpw3k Adaptive Immune Response (3rd line of defense): Speed: Slower to develop during the first encounter with a new pathogen. Effectiveness: Highly specific and effective against various pathogens. How it works: Tailors its response to target specific pathogens, learning and adapting over time. Cells of the adaptive immunity: B-lymphocytes and T- lymphocytes https://www.youtube.com/watch?v=jl4jo-zGmdI  Lymphocytes in Adaptive Immune Responses Essential cells in adaptive immune responses, mainly divided into B cells and T cells based on surface markers and functions. B Cells: Originate in red bone marrow, produce antibodies that bind to antigens on pathogens. Once activated by antigens, differentiate into plasma cells that secrete soluble antibodies. T Cells: Originate in bone marrow but mature in the thymus. Have varied functions, including releasing signaling molecules and eliminating cells infected with intracellular pathogens. Plasma Cells: Specialized B cells activated by antigens and capable of secreting antibodies. Differ in appearance from typical B and T cells due to high cytoplasm packed with protein- producing machinery. Natural Killer Cells (NK): Participants in the innate immune response. Circulating blood cells with cytotoxic granules, capable of destroying infected cells. Key players in defending against viruses and certain types of cancer. Antibodies Antibody Basics: Antibodies, also known as immunoglobulins (plasma proteins), are molecules crucial in the immune system's defense. They're secreted versions of B cell receptors and are integral to recognizing and neutralizing pathogens. Genetic Similarity: The same genes code for both secreted antibodies and surface immunoglobulins (B cell receptors). A minor difference in their production process distinguishes naive B cells (with antibodies on their surface) from plasma cells (secreting antibodies). Antibody Classes: Humans have five different classes of antibodies: IgM, IgD, IgG, IgA, and IgE. Each class has distinct roles in the immune response, contributing various critical functions to adaptive immunity https://www.youtube.com/watch?v=_N1xX49AqwQ Types of Lymphocytes  B and T Cell Development Critical for Adaptive Immune Response: Understanding how B and T cells develop is crucial to understanding how the body learns to fight pathogens without harming its own cells. Primary Lymphoid Organs: Include the bone marrow and thymus gland. Role in Lymphocyte Development: These organs are where lymphocytes grow, increase in number, and are trained to recognize and attack harmful invaders while leaving the body's own cells unharmed.  Secondary Lymphoid Organs and Active Immune Responses Role of Secondary Organs: Lymphocytes mature in primary organs but respond to antigens in secondary lymphoid organs. Lymph Nodes, Spleen and Others: lymphocytes gather Naïve Lymphocytes: Functional but haven't encountered antigens yet. Common Features of Secondary Organs: Lymphoid follicles, reticular fiber internal structure, germinal centers, high endothelial venules. Two processes happening in immunity Phagocytosis Cell lysis Phagocytes and Phagocytosis Phagocyte – Phago =“to eat” Cyte =“cell” The immune System Cleaner Job: Engulf and eat up particles or cells in a process called phagocytosis. What They Do: Clean up waste, old cells, or fight bad germs like bacteria. First Line of Defense: Quick and strong defenders against germs that sneak past our body's defenses into our vulnerable tissues. Phagocytosis https://en.wikipedia.org/wiki/Phagocytosis#/media/File:Process_of_Phagocytosis.svg  https://www.youtube.com/watch?v=TNK3WyEI3r8 Types of Phagocytes Macrophages – Versatile Defenders: Shape and Movement: Irregular-shaped, adaptable cells that move around and squeeze through capillary walls. Present in high numbers in lymph nodes and perform phagocytic functions. Roles: Not only part of the quick immune response but also cooperate with other cells for a stronger defense. Found in various tissues with different names. Neutrophils – Infection Reinforcements: Attracted to Infections: Spherical cells called granulocytes that rush from the blood to infected areas. Difference from Macrophages: Contains granules in the cytoplasm with substances like histamine, acts as a reinforcement in the battle against germs. Monocytes - Precursor Cells: Role: Circulating cells that can become macrophages or dendritic cells and are quickly drawn to areas of infection by inflammatory signals. Natural Killer Cells (NK Cells) Cell Actions: Induce apoptosis (programmed cell death) in infected cells harboring intracellular pathogens like certain bacteria and viruses. Recognition Mechanisms: Identify infected cells through unclear surface receptor mechanisms. Two Apoptosis Mechanisms: Fas Ligand Interaction: Express Fas ligand on their surface to bind with the Fas molecule on the infected cell's surface, signaling apoptosis for cell and pathogen destruction. Granule Release: NK cells release perforins (form membrane pores) and granzymes (enzymes that trigger apoptosis inside the cell). Effectiveness Against Viruses: Prevent release of infectious virus particles by inducing apoptosis before the completion of the virus replication cycle, halting further infection. Inflammation Inflammation is a complex cellular process involving various types of immune cells, clotting proteins and signaling molecules. Versus Infection refers to the invasion and multiplication of bacteria or viruses within the body, while inflammation is the body's protective response against infection. Inflammatory Response Inflammation is a key part of the body's response to tissue damage. Common signs include heat, redness, pain, and swelling (sometimes, a "loss of function" is also observed). It doesn’t only occur due to infections but can also happen with injuries. E.g. a cut or stubbing a toe triggers inflammation by releasing damaged cellular components. This response helps bring phagocytic cells to clean the area and begin the healing process. Inflammatory Response Tissue Injury: Injured cells release substances that trigger mast cells, leading to the release of inflammatory mediators causing swelling and increased blood flow. Inflammatory mediators attract immune cells like neutrophils and macrophages to the site. Vasodilation: Mediators cause blood vessels to widen, increasing blood flow and causing redness and warmth in the affected area. Increased Vascular Permeability: Inflammatory mediators make blood vessels more permeable, resulting in fluid leakage and swelling. Recruitment of Phagocytes: Mediators attract immune cells to remove debris and fight infection. Accumulated dead immune cells form pus in severe infections. Overall Role of Inflammation: Eliminates pathogens and debris. Aids in clotting and initiates wound repair. Facilitates immune response by transporting antigens to lymph nodes for adaptive immunity.  https://www.youtube.com/watch?v=XS30Rnpka8M Active vs Passive Immunity Active Immunity: Naturally Acquired Active Immunity: Developed as a response to a pathogen encountered by an individual. Artificially Acquired Active Immunity: Occurs through vaccination. Vaccines contain killed or weakened pathogens/components. Administered to induce immunological memory without severe symptoms. Prevents disease damage from first exposure to the pathogen. Significantly contributed to eradicating diseases like smallpox and controlling diseases such as polio, measles, and whooping cough. Passive Immunity: Natural Passive Immunity: Transfer of immune components from an immune individual to a non-immune individual. Artificial Passive Immunity: Involves the direct transfer of antibodies or immune components. Provides immediate but short-term protection. Examples include maternal transfer of antibodies to infants or injection of antibodies for rapid protection against specific diseases.