BY 312 Lecture (3/25)

Lymphatic System Overview

  • Functions of the Lymphatic System:

    • Formation of interstitial fluid

    • Transportation of dietary lipids

    • Facilitation of the immune response

Components of the Lymphatic System

  • Components discussed:

    • Lymphatic capillaries

    • Lymphatic vessels

    • Lymph nodes

    • Lymph trunks and ducts

    • Primary and secondary lymphatic organs

  • Overview of Lymph:

    • Definition and description of lymph as a clear, milky fluid in the extracellular fluid compartment.

    • Composition includes plasma, interstitial fluid, and absorbed dietary lipids in the GI tract.

Flow of Lymph

  • Direction of flow:

    • Always from periphery towards central vasculature.

    • Starts in interstitial fluid, moves to lymphatic capillaries, then to nodes, finally entering bloodstream at the subclavian veins.

  • Structure of Lymphatic Capillaries:

    • Larger than blood capillaries, one-way structure preventing fluid outflow, with overlapping cells.

    • Anchoring filaments help widen openings for fluid entry.

    • Specialized lacteals in the small intestine absorb dietary lipids, producing chyle, a white fluid.

Function of Lymphatic Vessels

  • Characteristics of lymphatic vessels:

    • Thinner walls than veins, multiple valves, and passing through lymph nodes.

    • Different types of vessels (afferent and efferent) for transport.

Factors Influencing Lymphatic Flow

  • Lymph is moved primarily by:

    • Pressure in the interstitial space

    • Skeletal muscle contractions

    • Respiratory movements create pressure variations, aiding flow.

Lymphatic Organs

  • Primary Lymphatic Organs:

    • Bone marrow and thymus where stem cells become immunocompetent.

Secondary Lymphatic Organs

  • Include spleen, lymph nodes, and tonsils, where immune responses are notably active.

  • Mention of the need for a capsule to qualify as a lymphatic organ.

Thymus Overview

  • Characteristics:

    • Location, capsule presence, cortex with immature T cells, and medulla with mature T cells.

    • Function in cell-mediated immunity.

  • Maturation process with dendritic cells; only about 25% of T cells survive.

  • Changes in the thymus size through life, including atrophy post-puberty.

Lymph Nodes' Role

  • Approximately 600 nodes serve to filter, trapping foreign objects in lymph:

    • Groups of regional lymph nodes include submandibular, cervical, axillary, mediastinal, anal, and iliac lymph nodes.

    • Flow of lymph through nodes includes afferent vessels into medullary sinuses and out through efferent vessels.

Lymph Node Diseases

  • Lymphadenopathy:

    • Defined as enlargement in size or texture, usually painless, could be a sign of cancer.

  • Lymphadenitis:

    • Inflammation of lymph nodes, usually painful, associated with infections.

  • Lymphangitis:

    • Inflammation of lymphatic vessels, possible causes encapsulated in the acronym "MIAMI" (malignancy, infection, autoimmune, miscellaneous, iatrogenic).

Breast Cancer Discussion

  • Definition: Development of a malignant tumor within breast tissue.

  • High risk of metastasis through axillary lymph nodes.

    • Lymphatic Drainage: About 75% occurs in the upper lateral quadrant, impacting metastasis patterns.

  • Cancerous lymph nodes tend to be enlarged, nontender, fixed in position, contrasting with lymphadenitis where nodes are tender and movable.

Spleen Overview

  • The largest mass of lymphatic tissue containing:

    • White pulp: Involved in immune function (contains lymphocytes, macrophages).

    • Red pulp: Contains blood-filled venous sinuses, stores platelets, and destroys old red blood cells.

  • Notable case of a surgeon mistakenly removing a liver instead of a spleen, which highlights the importance of differentiating between organs.

Clinical Procedures Involving the Spleen

  • Splenectomy: Removal of the spleen is necessary if it ruptures, often from trauma.

    • Function can potentially be compensated by red bone marrow but may result in reduced immune function.

Immune Response

  • Immune System Categories:

    • Innate immunity: Present at birth, nonspecific, includes skin and mucous membranes, produces antimicrobial substances, and utilizes natural killer cells.

    • Adaptive immunity: Takes time to develop, can be either cell-mediated or antibody-mediated.

  • Innate Immune Defenses:

    • First line includes physical barriers like skin and mucous membranes producing lysosomes.

    • Internal defenses include phagocytes (macrophages, neutrophils) and natural killer cells.

    • Discussed importance of microbiota in pathogen neutralization through various bodily systems.

Conclusion

  • The session concludes with a preview of further discussions on internal defense mechanisms of the immune system in the next lesson, focusing on various pathogen responses and definitions.