Lymphatic System Overview for Medical Students

Prayer Before Class

• A prayer is used before class to invoke guidance and wisdom.
• The prayer requests enlightenment, understanding and a clear mind
• The speaker requests help in successfully completing work.
• The speaker seeks help from the Holy Spirit, the Divine Creator.
• The prayer includes a request for protection from sin and ignorance.
• Guidance and success in expressing one's thoughts are requested.

Lymphatic System

• Topics included as part of the course curriculum.
• Lymphatic system physiology is part of the content.
• The sections of the course also include Innate and Adaptive Immunity, Diseases of the Lymphatic System relevant to the Philippines, and Diagnostic Tests for Lymphatic System Disorders relevant to Medical Technologists.
• Learning objectives include describing general lymphatic system functions and relating physiology to common diseases.

Lymphatic System Components

• Lymph
• Lymphatic vessels
• Lymphatic tissue
• Lymph nodules
• Lymph nodes
• Tonsils
• Spleen
• Thymus
• Right lymphatic duct
• Thymus
• Axillary lymph node
• Mammary plexus
• Lymphatic vessel
• Bone marrow

Overview of Lymphatic System

• Lymphatic capillaries and vessels remove excess fluid and absorb lipids from the small intestine.
• Lymph nodes filter and the spleen filters this fluid.

Functions of the Lymphatic System

• Fluid Balance: Approximately 30 Liters of fluid leave blood capillaries and enter tissues, with 27 returning to the bloodstream. The lymphatic system collects the remaining 3 Liters of excess fluid as lymph.
• Lipid Absorption: The lymphatic system absorbs lipids and other substances from the digestive tract via lacteals within the digestive lining. Lipids then enter lymphatic vessels and ultimately reach the venous circulatory system.
• Defense: Microorganisms and foreign substances are filtered from lymph by lymph nodes, and from blood by the spleen; lymphocytes and other cells destroy pathogens.

Anatomy of the Lymphatic System

• Lymphatic vessels start as small, closed tubes called capillaries.
• Excess fluid from tissues becomes lymph
• Lymphatic capillaries are present in most body tissues with exceptions.
• Lymphatic Capillaries lack a basement membrane and their endothelial cells overlap.
• The overlapping cells of the lymphatic capillary endothelium function as one-way valves, allowing fluid to enter the capillary but preventing backflow into the interstitial spaces.
• The lymph moves through lymphatic vessels via smooth muscle contractions, surrounding skeletal muscles, and the thoracic cavity's pressure changes.
• Lymph Nodes are round, oval, or bean-shaped bodies distributed along lymphatic vessels, filtering lymph, removing bacteria and other materials, and allowing lymphocytes to congregate and proliferate.
• Lymphatic trunks collect lymph from the lymph vessels, either connecting to larger veins in the thorax, or joining larger lymphatic ducts. These ducts empty into large veins, returning lymph to the circulatory system.
• The thoracic duct is the largest lymphatic vessel, approximately 38-45 cm long, draining lymph from the right side below the thorax, and the entire left side of the body.

Lymphatic Tissue and Organs

• Lymphatic nodules are denser arrangements of lymphatic tissue organized into compact, somewhat spherical structures. Peyer patches are aggregations of lymphatic nodules found in the distal half of the small intestine.

Lymph Nodes

• Lymph Nodes are small, round, or bean-shaped structures, ranging from 1 mm to 25 mm long.
• They're located along the course of lymphatic vessels, filtering lymph, removing bacteria, and other materials.
• Lymphocytes congregate and proliferate within lymph nodes.

Overview of Immunity

• Innate and Adaptive immunity are covered as part of the lymphatic system topic.

Immunity Concepts

• The ability to resist damage from foreign substances, harmful chemicals, and internal threats.
• The body has non-specific and specific immunity mechanisms.
• Specific immunity is acquired throughout life, recognizes substances, and respond even faster the second time it encounters them.
• Non-specific immunity exists from birth, and the body response is the same every exposure.
• Adaptive immunity can recognize specific substances; whereas innate immunity generally acts against a broad range of bacteria.
• Antibody-mediated immunity and cell-mediated immunity are aspects of adaptive immunity.
• Lymphocytes have the ability to recognize, respond to, and "remember" a particular substance (antigen).
• Foreign antigens: not produced by the body, introduced outside it
• Components of bacteria, viruses, others microorganisms, pollen, animal dander, food, drugs, and transplanted tissues and organs.
• Self-antigens: produced by the body to stimulate adaptive immune response
• Tumor and autoimmune diseases are examples of self-antigens.

Innate Immunity

• Physical barriers, white blood cells, and the inflammatory reaction are innate immunity mechanisms.

Innate Immunity: White Blood Cells

• Movement towards the source of chemotactic factors (Chemical signals.)
• Phagocytosis by phagocytes (Neutrophils and macrophages.)
• Destruction of microbes, parts of microbes, foreign substances and dead cells.

Innate Immunity: White Blood Cells

• Leukocytes (WBCs) (Monocytes, Macrophages, Basophils) are critical immunity components, produced in bone marrow, released into the bloodstream, and transported throughout the body for defense and tissue repair. WBCs are attracted to and migrate to infected/damaged tissues via chemical signals (chemotaxis.)
• Monocytes, once in tissues, mature into macrophages, becoming highly effective phagocytes (cells that engulf and destroy pathogens.)
• Basophils, mobile cells, release chemicals leading to inflammation (e.g., histamine).
• Mast cells remain within tissues and facilitate inflammation similarly to basophils.

Innate Immunity: Physical Barriers

• Prevent microbes from entering or physically remove them from surfaces; such as skin, mucous membranes, tears, saliva, urine, and Ciliated mucus membranes in the respiratory tract that move microbes to the back of the throat to be swallowed.

Innate Immunity: Chemical Mediators

• Include molecules such as lysozymes, histamine, interferons, complement proteins, and pyrogens.
• Lysozymes in tears and mucus break down microbial structures.
• Histamine and other mediators cause inflammation, vasodilation, increased permeability.
• Interferons interfere with viral replication.
• Complement proteins enhance inflammation, chemotaxis, and cell lysis.
• Pyrogens stimulate fever production..

Innate Immunity: Chemical Mediators

• Complement is a group of proteins destroying abnormal cells and boosting other immunity factors.
• Activated in a cascade, initially inactive but activated in the complement cascade for its function.

Innate: Alternative Pathway

• Complement activation initiated when C3 protein spontaneously activates;
• Activated C3 does not interact with microorganisms;
• Quickly inactivated;
• Combining activated C3 with foreign substances;
• Stabilizing activated C3 for complement cascade activation;
• Activated C3 and C5-9 destroying targeted cells (MAC.)

Adaptive Immunity

• The adaptive immune system involves B cells and T cells.

Adaptive Immunity: Antigens

• Foreign antigens (not produced by the body, introduced outside it)-- components of bacteria, viruses, other microorganisms, pollen, animal dander, food, drugs, transplanted tissues and organs.
• Self-antigens: produced by the body (tumor antigens, autoimmune diseases.)

Adaptive Immunity: Antibodies-mediated

• Involves proteins (antibodies) produced by B cells located in plasma, interstitial fluid, and lymph.
• Acts by directly inactivating or binding antigens together.
• Involved in Antibody-mediated immunity (involves proteins called antibodies--produced by B cells) and Cell-mediated immunity (involves cytotoxic T cells (CD8) and helper T cells (CD4)).

Adaptive Immunity: Lymphocyte Activation

• Lymphocytes recognize antigens.
• After recognition, lymphocytes increase in number to destroy antigens. -Cells become plasma cells/memory B cells.
• They form antibodies that work directly or indirectly to destroy antigens.
• Also, a quick effective response to previously reacted antigens; responsible for adaptive immunity.
• Naive T cells (CD4+ or CD8+) are activated via antigen recognition
• Cytokines (such as IL-2) facilitate proliferation, differentiation, and effector function.
• CD4+ T cells activate macrophages and other cells, CD8+ T cells kill infected cells.

Adaptive Immunity: Lymphocytes

• After activation, B cells become plasma cells or memory B cells, making antibodies.
• Memory B cells provide quick and effective response to previously reacted antigens (adaptive immunity).

Adaptive Immunity: Lymphocytes

• Cytotoxic T cells are responsible for destroying cells by lysis or producing cytokines.
• Helper T cells activate B cells and cytotoxic T cells
• Regulatory T cells inhibit B cells, helper T cells, and cytotoxic T cells.

Adaptive Immunity: Direct Effects of Antibodies

• Antibodies directly inactivate antigens by binding to them.
• Antibodies also bind multiple antigens together, making them easier to remove.

Adaptive Immunity: Indirect Effects of Antibodies

• Antibodies activate the complement cascade, producing inflammation, chemotaxis, and lysis.
• Antibodies also initiate the release of inflammatory chemicals by binding to mast cells or basophils.
• Antibodies facilitate phagocytosis when they bind to antigens, making them easier for macrophages to engulf and destroy.

Adaptive Immunity: Stimulation and Effects of T Cells

• Antigens activate T cells, which then divide and differentiate into cytotoxic and memory T cells.
• Cytotoxic T cells kill cells by directly contacting them.
• Memory T cells provide a rapid response to future exposures to the same antigen.

Acquired Adaptive Immunity

• Active immunity is built by an individual’s own immune system in response to antigens, whether encountered naturally or through artificial intervention via vaccines.
• Passive immunity is when immunity is transferred to another person, either from mother to child (natural) or via injection from another person/animal (artificial).

Disorders & Diagnostic Tests relevant to the Lymphatic System

• The course covers effects of aging on the lymphatic system and immunity (infections and hypersensitivities).
• Diagnostic tests included for disorders (e.g., complete blood count, ultrasound, fine needle aspiration, Gram stain, culture of aspirated tissue, allergy testing).
• Diseases like lymphadenitis, lymphangitis and bubonic plague are part of the infections of the lymphatic system.

Effects of Aging on the Lymphatic System & Immunity

• Aging can have little effect on the lymphatic system and removal related functions.
• However, aging significantly impacts the adaptive immune system, reducing thymus function, decreasing helper T-cell proliferation, and altering antibody responses.

Infections of the Lymphatic System

• Lymphadenitis is inflammation of the lymph nodes.
• Lymph nodes enlarge and become tender because microorganisms become trapped and destroyed.
• Lymphangitis is an inflammation of the lymphatic vessels, producing visible red streaks extending from the infection site.
• Bubonic plague (caused by Yersinia pestis): transmitted by flea bites from rats, causing infection, potentially leading to septicemia and death.

Infections of the Lymphatic System

• Bubonic plague is a bacteria infection spread to humans via flea bites from rats
• Black Death is a famous historical bubonic plague outbreak, historically significant

Diagnostic Tests

• Diagnostic tests for the lymphatic system and immunity are part of the study materials.

Immediate Hypersensitivities

• Symptoms develop within minutes of antigen exposure due to preexisting antibodies.
• Urticaria (hives): localized or widespread skin rash, often caused by ingested antigens.
• Allergic asthma: antigen combines with antibodies on mast cells in the lungs, releasing inflammatory chemicals leading to airway constriction and breathing difficulty.
• Anaphylaxis: a systemic allergic reaction that can lead to vasodilation, increased permeability, decreased blood pressure, and potentially death.
• Diagnostic tests for identifying the causes included elevated eosinophils and basophils; Allergy testing.

Review

• A review of the lymphatic system and immunity is included as part of the student material.

Formative Assessment

• Includes various formative assessment with questions related to the topics, assessing student understanding of the material previously discussed.