Lymphatic System, Immunity, and Microbiology Practice Flashcards
The Lymphatic System: Organization and Function
System Overview: The lymphatic system is a comprehensive network comprising organs, tissues, nodes, vessels, and a specific fluid known as lymph. This system is intimately associated with the Cardiovascular (CV) system.
Primary Functions: * Drainage of Interstitial Fluid: It drains excess fluid that leaks from the bloodstream into tissue spaces. This volume is approximately on a daily basis. * Transport of Dietary Lipids: It is responsible for the transportation of most lipids and lipid-soluble vitamins absorbed by the gastrointestinal tract. * Facilitation of Immune Response: It initiates highly specific responses against particular microbes or abnormal cells.
Relationship to Blood Vessels: * Lymphatic Capillaries: These are present between cells, positioned around blood capillaries to drain the surrounding fluid. They are unique for being "blind-ended" tubes. * Mini-valves: The endothelial cells of lymphatic capillaries overlap, acting as one-way mini-valves. These allow fluid, proteins, and larger particles such as bacteria and viruses to enter the lymphatic system but prevent them from leaking back out. * Circulation Pathway: Lymphatic capillaries join to form larger lymphatic vessels and ducts, which eventually return the collected fluid to the bloodstream.
Lymph Nodes: * Physical Characteristics: These are kidney-shaped organs measuring up to in diameter. * Distribution: Large collections of nodes are located in the neck (cervical), underarm (axillary), and upper thigh (inguinal) regions. * Quantity: There are approximately lymph nodes distributed throughout the human body. * Flow Dynamics: Lymph flows through these nodes in a strictly one-way direction to facilitate filtering.
Lymphatic Organs and Tissues: * Primary Lymphatic Organs: These include the red bone marrow and thymus. They serve as the sites where stem cells divide and develop into immunocompetent cells (cells capable of mounting an immune response). * Secondary Lymphatic Organs and Tissues: These include lymph nodes, the spleen, and lymphatic nodules (follicles). These are the specific sites where the majority of actual immune responses occur.
Innate Immunity: The First and Second Lines of Defense
Definition of Innate Immunity: A general, non-specific form of defense that is present at birth. It acts immediately or very quickly against any potential pathogen.
First Line of Defense (Physical and Chemical Barriers): * Intact Skin: Provides a physical barrier to prevent entry. * Mucous Membranes: Line body cavities open to the exterior; they produce mucus to trap particles. * Conjunctiva of the Eye: Protected by the flushing action of tears. * Lysozyme: An enzyme found in tears and saliva that destroys bacterial cell walls. * Cilia: Found in the trachea to move trapped particles upward for removal via coughing or sneezing. * Stomach Acid: Highly acidic environment that destroys many ingested bacteria. * Urinary Tract: The flushing action of urine helps clear the tract of pathogens. * Commensal Organisms: "Good bacteria" in the gut, vagina, and on the skin that outcompete pathogens.
Second Line of Defense: * Phagocytes: Primarily neutrophils and macrophages. * Monocytes: Circulate in the blood and migrate to tissues to become macrophages. * Chemotaxis: The process by which phagocytes are attracted to an area of damage or infection. * Fixed Phagocytes: Located permanently in the skin, liver, lungs, brain, spleen, lymph nodes, and red bone marrow. * Phagocytosis Process: 1. Attraction: Phagocyte is drawn to the infected area. 2. Adherence: The phagocyte attaches to the microbe. 3. Ingestion: The phagocyte engulfs the microbe, encasing it in a vesicle called a phagosome. 4. Digestion: The phagosome merges with a lysosome, where enzymes destroy the pathogen. * Natural Killer (NK) Cells: * Account for of lymphocytes in the blood. They are also found in the spleen, nodes, and red bone marrow. * Function: They recognize abnormal proteins on plasma membranes (such as cancer cells or virus-infected cells). * Mechanism: Release Perforins (to create perforations/pores in the cell membrane) and Granzymes (protein-digesting enzymes that induce cell death/apoptosis). * Inflammation: * Signs: Characterized by pain, redness, heat, and swelling (edema). * Initial Stage: Damage occurs; mast cells and damaged cells release inflammatory mediators like histamine. This causes vasodilation (widening of arterioles) and increased capillary permeability. * Later Stage: Local macrophages are activated. Neutrophils undergo margination (sticking to capillary walls) and diapedesis (squeezing through walls) to reach the tissue. * Leukocytosis: The bone marrow increases production of white blood cells to meet the demand. * Fever: * Defined as an abnormally high body temperature triggered by pyrogens. * The hypothalamus resets the body's thermostat to a higher level. * Benefits: Inhibits bacterial/viral growth, enhances interferon effects, and speeds up metabolic rates for tissue repair. * Antimicrobial Substances: * Interferons (IFNs): Proteins released by virus-infected cells that warn neighboring cells to synthesize proteins that "interfere" with viral replication. * Complement System: A group of over inactive plasma proteins. When activated, they enhance inflammation (releasing histamine), cause opsonization (coating a microbe to make it easier for phagocytes to bind), and create a Membrane Attack Complex (MAC) that causes cell lysis.
Adaptive Immunity: The Third Line of Defense
Key Characteristics: Also known as specific immunity. It recognizes specific antigens, is systemic (not limited to the infection site), and possesses memory, allowing for a faster and stronger response upon second exposure.
Antigens: Any substance that causes the immune system to produce antibodies (derived from "Antibody Generator"). * Foreign Antigens: Found on bacteria, viruses, toxins, and foreign tissues (transplants). * Self-Antigens: Markers on our own cells that the immune system ignores, such as A, B, and Rh antigens on red blood cells, and Major Histocompatibility Complex (MHC) antigens.
Antigen-Presenting Cells (APCs): These include dendritic cells, macrophages, and B cells. They engulf pathogens, package the foreign antigen with MHC molecules, and display the complex on their surface to "present" it to T cells.
Lymphocytes: Humans carry approximately () lymphocytes, weighing about . * T cells: Thymus-derived. * B cells: Bone marrow-derived. * NK cells: Natural Killer cells.
B Cell Activation and Humoral Immunity: * Includes a three-step process: Antigen binding, Activation (typically via Helper T Cells), and Division/Differentiation. * Plasma Cells: Differentiated B cells that secrete antibodies into the blood/lymph. * Memory B Cells: Long-lived cells that provide lasting protection.
Antibody Structure and Classes: * Structure: T- or Y-shaped monomer consisting of four polypeptide chains (two heavy, two light). Includes a Variable region (antigen-binding site) and a Constant region (determines antibody class). * Classes: * IgG: Most abundant in serum; the only type that crosses the placenta. * IgA: Found in secretions (milk, saliva); prevents attachment to epithelia. * IgM: The first class secreted upon primary exposure; a potent agglutinating agent. * IgE: Binds to mast cells and basophils; involved in allergic reactions. * IgD: Found on the surface of B cells; involved in B cell activation.
Antibody Mechanisms of Action: * Agglutination/Precipitation: Clumping antigens together. * Opsonization: Coating antigens to enhance phagocytosis. * Neutralization: Blocking the toxic effects of pathogens or toxins. * Complement Activation: Leading to cell lysis. * Stimulation of Inflammation: Specifically via IgE and mast cells.
Cell-Mediated Immunity: * Helper T Cells (CD4+): Recognize antigens on APCs; release cytokines to activate B cells and Cytotoxic T cells. * Cytotoxic T Cells (CD8+): Directly attack and kill virus-infected, cancerous, or foreign graft cells using perforins and granzymes. * Regulatory T Cells (CD4+, CD25+): Suppress T and B cell activity once the antigen is cleared to prevent autoimmune damage.
Infectious Microbiological Agents
Major Groups: Fungi, Algae, Protozoa, Bacteria, and Viruses.
Classification by Lifestyle: * Detritivores/Saprophages: Live on dead/decaying matter. * Symbionts: Include Commensals (one benefits, no harm to other), Mutuals (both benefit), and Parasites (one benefits, other is harmed).
Fungi: Eukaryotes with a rigid cell wall made of chitin-glucan polymers. * Yeasts: Unicellular (e.g., Candida, Saccharomyces). * Moulds: Multicellular (e.g., Penicillium, used to create the antibiotic Penicillin which inhibits bacterial cell wall synthesis). * Mycoses: Types include Superficial, Cutaneous (e.g., Tinea pedis or Athlete's Foot), Subcutaneous, and Systemic.
Protozoa: Unicellular eukaryotes () often found in water/soil. * Example: Malaria is caused by Plasmodium parasites injected by mosquitoes. They develop in the liver and eventually rupture red blood cells.
Bacteria: Prokaryotic organisms (no nucleus/organelles). * Example 1: Escherichia coli (E. coli) replicates extremely fast (from to in ). * Example 2: Periodontitis is caused primarily by Porphyromonas gingivalis, where the immune system's release of Reactive Oxygen Species (ROS) damages both the bacteria and host tissue.
Viruses: Non-cellular, obligate intracellular parasites containing DNA or RNA surrounded by a capsid (protein shell). * Influenza Virus: Uses Haemagglutinins (H) (18 identified types) to bind to cells and Neuraminidase (N) (9 identified types) to release new viral particles. * Replication Cycle: Attachment → Endocytosis → Release of viral contents → RNA replication in nucleus → Viral protein synthesis → New particle assembly and release. * Mutations: Viruses lack DNA stability mechanisms, causing frequent mutations and different strains, making them difficult for the adaptive immune system to track.
NSQHS Standards 2021: The "Preventing and Controlling Infections Standard" outlines four criteria: 1. Clinical governance and quality improvement. 2. Infection prevention and control systems (precautions, hand washing, aseptic technique). 3. Reprocessing reusable equipment. 4. Antimicrobial stewardship (appropriate prescribing).