Lymphatic System Quiz

Lymphatic System Overview

• The lymphatic system is a network of vessels, tissues, and organs that helps maintain fluid balance, absorb fats, and defend against pathogens.

Functions of the Lymphatic System

• Fluid Balance: Approximately 30 liters of fluid pass from blood capillaries into interstitial spaces daily; 27 liters return to the blood capillaries. The remaining 3 liters enter lymphatic capillaries, becoming lymph, and are returned to the circulatory system.
• Fat/Lipid Absorption: The lymphatic system absorbs lipids and other substances (e.g., fats, fat-soluble vitamins) from the digestive tract via lacteals in the small intestine. Lymph containing lipids is called chyle and appears white.
• Defense: The lymphatic system filters lymph (via lymph nodes) and blood (via the spleen) to remove pathogens (e.g., microorganisms) and foreign substances. Lymphocytes and other cells destroy pathogens. The system combats infections.

Components of the Lymphatic System

• Lymph: Fluid that enters lymphatic capillaries, composed of water and solutes.
• Lymphocytes: Cells crucial for adaptive immunity.
• Lymphatic Vessels: Carry lymph; resemble veins with one-way valves.
• Lymph Nodes: Rounded structures found near lymphatic vessels in the groin, armpits, and neck. Lymph passes through nodes before entering the blood; they filter lymph and activate the immune system when necessary.
• Tonsils: Lymphatic tissue in the oral and nasal cavities, forming a protective ring.
• Spleen: Filters blood and is a site where lymphocytes respond to infections. It is clenched fist-sized and located in the abdomen.
• Thymus Gland: A bilobed gland in the mediastinum; site for maturation of T cells. The thymus produces and matures lymphocytes (T cells).

Lymphatic Capillaries and Vessels

• Lymphatic capillaries are tiny, closed-ended vessels where fluid moves easily into tissues.
• Lymphatic capillaries join to form lymphatic vessels, which resemble small veins with one-way valves to prevent backflow.

Lymphatic Ducts

• Right Lymphatic Duct: Receives lymph from the right upper limb and right side of the head, neck, and chest, emptying into the right subclavian vein.
• Thoracic Duct: Receives lymph from the rest of the body, emptying into the left subclavian vein.

Lymph Node Structure

• Lymph nodes are rounded structures, varying in size, located near lymphatic vessels (groin, armpit, and neck).
• Lymph flows through sinuses in the lymph node.
• Phagocytic cells remove foreign substances. Germinal centers are sites of lymphocyte production.

Spleen Structure and Function

• The spleen is roughly the size of a clenched fist, located in the abdomen.
• It filters blood and contains white pulp (lymphatic tissue around arteries) and red pulp (macrophages and red blood cells that connect to veins). It detects, responds to, and destroys foreign substances and old red blood cells. It acts as a blood reservoir.

Thymus Gland Structure and Function

• The thymus gland is a bilobed gland located in the mediastinum behind the sternum.
• It's the site where T cells mature.

Lymphatic Organs (Tonsils)

• Palatine tonsils are on each side of the oral cavity.
• Pharyngeal tonsils are near the internal opening of the nasal cavity (adenoids).
• Lingual tonsils are on the posterior surface of the tongue.
• They form a protective ring of lymphatic tissue around the nasal and oral cavities.

Immunity

• Immunity is the ability to resist damage from foreign substances, like microbes, toxins, and cancer cells. It has innate and adaptive components.

Innate Immunity

• Present at birth.
• Provides defense against any pathogen.
• Achieved via physical barriers, chemical mediators (e.g., lysozyme), cells (e.g., phagocytes), and inflammatory response.

Physical Barriers (Innate)

• Skin and mucous membranes act as barriers.
• Tears, saliva, and urine wash away pathogens.

Chemical Mediators (Innate)

• Chemicals that kill microbes and prevent their entry into cells. Examples include lysozyme (tears, saliva) that kill bacteria, mucous membranes that prevent microbe entry, histamine, and interferons.

Cells (Innate)

• White blood cells produced in red bone marrow and lymphatic tissue.
• Phagocytic cells (e.g., neutrophils, macrophages) ingest and destroy foreign substances.
• Basophils release histamine; mast cells release leukotrienes.
• Eosinophils release chemicals to reduce inflammation.
• Natural killer cells recognize and destroy tumor or virus-infected cells.

Inflammatory Response (Innate)

• Involves chemicals and cells due to injury or foreign substance.
• Stimulates the release of chemical mediators, leading to local inflammation.
• Symptoms include redness, heat, swelling, and pain.
• Can be systemic, affecting multiple body areas. The effects include large neutrophil release, fever promotion, decreased blood volume.

Adaptive Immunity

• Acquired after birth.
• Reacts when innate defenses don't work.
• Slower than innate immunity, but has memory.
• Relies on lymphocytes (B and T cells).
• Two main types: antibody-mediated and cell-mediated immunity.

Adaptive Immunity Components

• Antigen: A substance that stimulates an immune response (e.g., bacteria, viruses).
• Self-antigen: Molecules produced by the body that stimulate immune responses.
• Antibody: Proteins produced by the body in response to an antigen.
• MHC (Major Histocompatibility Complex): Molecules that hold and present processed antigens on cell membranes.

Lymphocytes: Origin and Development

• Originate from stem cells in red bone marrow.
• Different stem cells develop into B cells and T cells, which travel through circulation and mature in specific environments.

B-cells

• Involved in antibody-mediated immunity.
• Mature in the red bone marrow.
• Move to lymphatic tissue to produce antibodies after maturation.

T-cells

• Involved in cell-mediated immunity.
• Mature in the thymus.
• Move to lymphatic tissue after maturation.

Antigen Recognition

• Lymphocytes have specific antigen receptors on their surfaces.
• B-cell receptors and T-cell receptors bind to specific antigens.
• Antigen receptor binding activates lymphocytes, initiating adaptive immunity.

Cytokines

• Signaling proteins secreted by cells that regulate neighboring cells impacting the immune response and cell growth. Examples include interleukin 1 released by macrophages to stimulate helper T cells.

Antibody Production

• Primary Response: The first exposure of a B cell to an antigen results in the division of the B cell into plasma cells and memory cells. Plasma cells produce antibodies targeting the antigen to fight pathogens. This process takes 3-14 days from initial contact until the body effectively combats the antigen.
• Secondary Response: The response when the immune system encounters the same antigen again. The memory cells quickly divide to form plasma cells, which produce antibodies that are more concentrated and faster in action than the primary response.

Cell-Mediated Immunity

• Effective against antigens within cells and tissues, particularly against bacteria, viruses, fungi, and protozoa.
• Relies on different types of T cells to directly combat these pathogens. Types of T-cells include helper T cells (T_H), cytotoxic T cells (T_C) and regulatory T cells (T_reg).

Different Types of T Cells

• Helper T cells (TH): These cells activate macrophages and help B cells form. They also help T-cell proliferation. They aid in antibody production.
• Cytotoxic T cells (TC): These cells directly kill cells infected with antigens.
• Regulatory T cells (Treg): These cells turn off the immune system response once the antigen is gone, preventing excessive or prolonged immune responses.

Types of Adaptive Immunity

• Naturally Acquired Active Immunity: Exposure to antigens through natural infection produces antibodies (and memory).
• Naturally Acquired Passive Immunity: Transfer of antibodies from mother to child (breast milk, placenta).
• Artificially Acquired Active Immunity: Exposure to antigens (e.g., vaccines) to stimulate antibody production.
• Artificially Acquired Passive Immunity: Injection of antibodies from an animal to passively provide protection against a specific disease.