Lymphatic System

Lymphatic System Structures

  • Lymphatic Catheters
      - Embedded within connective tissue.
      - Most likely in areolar tissue.

  • Fluid Collection and Edema
      - Importance of collecting weak fluid:
        - Prevent loss of blood volume.
        - Loose connective tissue absorbs fluid, which can lead to edema (swelling).

Lymphatic Capillaries

  • Definition
      - Also known as hemocytes.

  • Function
      - Collect fluid from the connective tissue and return it to the heart.

  • Structure
      - Feature flap-like mini valves (slits).
      - Fluid concentration gradient:
        - High concentration in connective tissue, low in lymphatic vessels.
        - Fluid moves through mini valves due to pressure gradients.

  • Fluid Flow Mechanism
      - High pressure in the vessel shuts mini valves, aiding in fluid movement back to the heart.
      - Movement facilitated by skeletal muscle contraction and breathing (pressure changes).
      - Connection to yoga: Promotes lymphatic function.

Lymphatic Drainage Ducts

  • Right Lymphatic Duct
      - Drains fluid from the right side of:
        - Head.
        - Cervical region.
        - Thoracic region.
        - Right arm.

  • Thoracic Duct
      - Drains fluid from:
        - Left head.
        - Left cervical region.
        - Left thoracic region.
        - Both legs.
        - Pelvic and abdominal cavities.

  • Destination of Lymph
      - Both ducts return lymph to the right atrium of the heart.

Lymph Nodes

  • Definition
      - Tiny structures through which lymph fluid passes before returning to the heart.

  • Location
      - Scattered throughout the body:
        - Neck.
        - Axillary region.
        - Groin.
        - Small intestine (Peyer's patches).

  • Vessels
      - Afferent vessels: Carry lymph to the lymph node.
      - Efferent vessels: Carry lymph away from the lymph node.

  • Why More Afferent Than Efferent?
      - To allow for thorough cleaning of lymph fluid as it passes through.

  • Analogy
      - Similar to sand flowing through an hourglass, slowing down for processing.

Immune System Overview

  • Innate Immune Responses
      - Two types: Nonspecific defenses.
      - First Line of Defense:
        - Mechanical barriers: Intact skin, mucous membranes, acidity levels of sweat and sebum.
        - Cells: Neutrophils, macrophages, phagocytes, known as nonspecific cells.
        - Role of phagocytes: Ingest pathogens, break them down, can serve as antigen-presenting cells.

  • Natural Killer Cells
      - Function: Circulate in lymph, identify and destroy foreign entities by puncturing their membrane.

  • Antimicrobial Proteins
      - Function: Fixation of complements leading to inflammation and cell lysis.

  • Inflammatory Response
      - Symptoms: Pain, heat, swelling, redness.
      - Causes: Increased blood flow and capillary permeability, recruitment of immune cells to the infection site.

  • Fever
      - Mechanism: Hypothalamus increases body temperature to limit bacteria access to nutrients like zinc.

  • Third Line of Defense
      - Subdivided into two arms:
        - Humoral (B cells).
        - Cell-mediated (T cells).

Specific Immune Responses

  • B Cells
      - Produced in bone marrow; capable of binding to free antigens.
      - Upon activation, proliferate to form plasma cells (secrete antibodies) and memory B cells (for future responses).

  • T Cells
      - Developed in the thymus; require antigen presentation.
      - Helper T Cells: Activate cytotoxic T cells and B cells.
      - Cytotoxic T Cells: Directly kill infected cells by releasing perforin and granzymes, causing cell death.

  • Immunocompetency
      - Definition: Ability of lymphocytes to bind to specific antigens.

Types of Immunity

  • Active Immunity
      - Occurs when the individual produces their own antibodies through natural exposure or vaccines.

  • Passive Immunity
      - Temporary immunity gained from receiving antibodies, either naturally (e.g., breastfeeding) or artificially (e.g., serum injection).

Antibody Classification

  • Classes of Antibodies (MADGE)
      - IgM: Effective in complement fixation and cell lysis.
      - IgA: Found in mucosal areas (e.g., tears, saliva).
      - IgD: Activates T cells.
      - IgG: Most abundant; crosses the placental barrier.
      - IgE: Involved in allergic responses.

Function of Antibodies

  • Mechanisms of Action
      - Neutralization: Marks toxins for destruction.
      - Agglutination: Clumping of pathogens for phagocytosis; important in blood typing.
      - Precipitation: Similar to agglutination, leading to phagocytosis.
      - Complement Fixation: Triggers inflammatory responses, phagocytosis, and cell lysis.

Antigen Presentation

  • Process
      - Antigen presenting cells (APC) present antigen fragments to helper T cells.
      - Activated helper T cells stimulate cytotoxic T cells and B cells, enhancing both humoral and cell-mediated immunity.

Conclusion of Immune Response

  • Regulatory T Cells
      - Function: Regulate and stop the immune response to prevent autoimmune disorders.

Grafts

  • Types of Grafts
      - Autografts: Tissue from oneself.
      - Isografts: Tissue from an identical twin.
      - Allografts: Tissue from a genetically similar donor.
      - Xenografts: Tissue from a different species, often unsuccessful.