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    Related Topics

    From Lymphatic System

    Tubal Tonsils
    Near openings of the auditory tubes.
    Lateral Axillary Nodes
    Located along the humerus in the axilla.
    Axillary Lymph Nodes
    Drain the upper limbs and chest wall.
    Mastoid Lymph Nodes
    Drain the posterior scalp and ear.
    Peyer’s Patches
    Lymphoid nodules in the small intestine.
    Parotid Lymph Nodes
    Drain the lateral face and scalp.
    Para-aortic Lymph Nodes
    Drain abdominal viscera and lower limbs.
    MALT
    Mucosa-associated lymphoid tissue.
    Mesenteric Lymph Nodes
    Drain the intestines and abdominal structures.
    GALT
    Gut-associated lymphoid tissue.
    Submental Lymph Nodes
    Drain the floor of the mouth and central lower lip.
    Intestinal Trunk
    Drains lymph from the intestines.
    Pharyngeal Tonsil
    Located in the nasopharynx (adenoids).
    Lymphatic Collecting Vessels
    Carry lymph through lymph nodes.
    Palatine Tonsils
    Located on each side of the oropharynx.
    Thoracic Duct
    Main lymphatic duct draining most of the body.
    Red Bone Marrow
    Produces lymphocytes; site of B-cell maturation.
    Pectoral Axillary Nodes
    Located along the anterior chest wall.
    Anterior Mediastinal Nodes
    Drain anterior thoracic structures.
    Supraclavicular Lymph Nodes
    Located above the clavicle; key in thoracic drainage.
    Pretracheal Nodes
    Located anterior to the trachea.
    Inguinal Lymph Nodes
    Drain the lower limbs and external genitalia.
    Apical Axillary Nodes
    Located at the apex of the axilla.
    Appendix
    Lymphoid-rich structure of the large intestine.
    Subscapular Axillary Nodes
    Located along the posterior chest wall.

    Lymphatic Capillaries

    Reviewed by our medical team

    Initial lymphatic vessels that collect interstitial fluid.

    1. Overview

    Lymphatic capillaries are the smallest and most distal vessels of the lymphatic system. They serve as entry points for interstitial fluid, macromolecules, pathogens, and immune cells into the lymphatic circulation. Unlike blood capillaries, lymphatic capillaries are highly permeable and designed to collect excess fluid and large molecules that cannot reenter venous capillaries. They play a critical role in maintaining tissue fluid balance, initiating immune responses, and facilitating the transport of dietary lipids from the intestines.

    2. Location

    Lymphatic capillaries are found throughout most tissues of the body, closely associated with blood capillary networks. Specific locations include:

    • Dermis of the skin

    • Mucosal membranes (e.g., respiratory, digestive, and urogenital tracts)

    • Villi of the small intestine (where they form lacteals)

    • Connective tissues surrounding blood vessels and organs

    They are absent in some specialized tissues, such as the central nervous system (CNS parenchyma), bone marrow, and avascular tissues like cartilage and the cornea. In the brain, lymphatic-like functions are performed by the glymphatic system and meningeal lymphatics.

    3. Structure

    Lymphatic capillaries have a distinct structure adapted for absorbing fluid and large molecules:

    • Endothelium: Composed of a single layer of thin, overlapping endothelial cells that function like one-way valves.

    • No basement membrane: Unlike blood capillaries, they lack a continuous basement membrane, allowing high permeability.

    • Anchoring filaments: Attach endothelial cells to surrounding connective tissue; these filaments prevent collapse under high interstitial pressure and open the capillary when pressure rises.

    • Valveless structure: Lymphatic capillaries lack smooth muscle and valves at this level, relying on tissue pressure gradients for fluid movement.

    These features make lymphatic capillaries highly efficient at absorbing not only fluid, but also proteins, cell debris, microbes, and even cancer cells.

    4. Function

    Lymphatic capillaries perform several essential functions as the initial segment of the lymphatic system:

    • Fluid uptake: Absorb excess interstitial fluid that leaks out of blood capillaries.

    • Macromolecule transport: Remove proteins, lipids, and other large molecules from interstitial spaces.

    • Immune surveillance: Capture antigens and allow dendritic cells to enter the lymphatics and travel to lymph nodes for immune processing.

    • Fat absorption: In the intestines, specialized lymphatic capillaries called lacteals absorb dietary lipids and chylomicrons for delivery to the bloodstream.

    5. Physiological Role(s)

    Lymphatic capillaries are critical to multiple homeostatic and immune functions:

    • Tissue fluid balance: Prevent tissue swelling (edema) by returning filtered plasma to circulation via lymphatic vessels.

    • Immune cell trafficking: Serve as a route for antigen-presenting cells and lymphocytes to reach lymph nodes.

    • Resolution of inflammation: Help clear inflammatory mediators and immune cells from injured tissues.

    • Lipid transport: Enable the absorption of fats and fat-soluble vitamins (A, D, E, K) from the gut through lacteals.

    6. Clinical Significance

    Lymphedema

    Dysfunction or blockage of lymphatic capillaries impairs lymph drainage, leading to lymphedema—a condition characterized by chronic swelling due to fluid accumulation. Causes include:

    • Congenital malformations (primary lymphedema)

    • Infection (e.g., filariasis)

    • Post-surgical or radiation damage (common in cancer treatment)

    Inflammatory and Autoimmune Conditions

    In diseases like rheumatoid arthritis and psoriasis, lymphatic capillary dysfunction may contribute to unresolved inflammation and impaired immune regulation.

    Cancer Metastasis

    Cancer cells can enter lymphatic capillaries and spread to regional lymph nodes. The permeability and lack of basal lamina in these vessels make them susceptible to invasion by tumor cells, particularly in breast, melanoma, and gastrointestinal cancers.

    Infections

    Pathogens like bacteria and viruses can access the lymphatic system via capillaries, leading to lymphangitis or systemic infections. Some viruses (e.g., HIV) use lymphatics to reach lymph nodes and disseminate.

    Therapeutic Targeting

    Because of their role in immune cell trafficking and drainage, lymphatic capillaries are being explored as delivery routes or targets for:

    • Vaccines

    • Anti-inflammatory drugs

    • Cancer immunotherapies

    Did you know? Lymphatic capillaries, the smallest of the lymphatic vessels, are extremely thin-walled and allow for the uptake of interstitial fluid.