2/26/25

General Overview

  • The lymphatic system complements the circulatory system by returning excess fluid from interstitial spaces to venous circulation.

Class Structure

  • Lecture sheets are available in class and on Canvas.

  • PowerPoint presentation will be posted for students, especially due to requests from Kylie.

  • Group quiz instructions will be provided, allowing students to self-select their groups, aiming for 5 members per group.

  • Quiz will occur on the upcoming Monday after feedback is received on group selection process.

Lymphatic System Functions

Primary Roles

  1. Return Excess Fluid

    • Lymphatic vessels collect excess fluid (lymph) from interstitial spaces not returned to venous circulation via capillaries.

  2. Cleansing of Fluid

    • These vessels cleanse the lymph of waste products, toxins, and pathogens.

  3. Immune Function

    • Specific structures in the lymphatic system support immune function, aiding in the detection and response to foreign invaders.

Movement of Lymph

  • Lymph circulates in a one-directional flow toward the heart, similar to blood flow.

  • Lymphatic capillaries are more permeable than vascular capillaries, capable of taking up larger molecules, including proteins, cell debris, pathogens, and cancer cells.

  • They utilize overlapping cells to create mini valves that open in response to interstitial fluid pressure.

Anatomy of Lymphatic Vessels

  • Lymphatic vessels grow larger as they approach the heart.

  • Similar in structure to veins but with thinner walls, enhancing permeability.

  • Frequent anastomosis leads to variable locations of lymphatic vessels compared to the more fixed locations of arteries and veins.

Lymph Fluid

  • Lymph is the fluid found within lymphatic vessels, derived from interstitial fluid and cleansed of waste.

  • It exits the lymphatic system at the junction of the jugular and subclavian veins, merging with blood and becoming part of the vascular system again.

Immune Functions of the Lymphatic System

  • Lymphatic structures play a crucial role in immunological response, cleansing lymph potentially loaded with pathogens or cancer cells.

  • Lack of proper immune function can result in metastasis of cancer.

Types of Lymphoid Cells

  1. Lymphocytes

    • T Cells: Attack foreign invaders directly.

    • B Cells: Produce antibodies after becoming plasma cells.

  2. Macrophages

    • Phagocytic cells that eliminate foreign substances.

  3. Dendritic Cells

    • Capture foreign invaders and present them to the immune system.

  4. Reticular Cells

    • Create fibrous stroma to support immune cells in lymphoid tissues.

Lymphoid Tissues

  • Diffuse Lymphoid Tissue: Scattered throughout the body, often concentrated in mucous membranes (mouth, GI tract, urogenital tract).

  • Lymphoid Follicles/Nodules: Spherical aggregates that facilitate B cell maturation and proliferation.

Lymphoid Organs

  1. Primary Lymphoid Organs

    • Red bone marrow: Site of origin for lymphocytes.

    • Thymus: Site for T cell maturation.

  2. Secondary Lymphoid Organs

    • Lymph nodes, spleen, MALT (Mucosa-Associated Lymphoid Tissue).

    • Areas where lymphocytes become activated after initial contact with foreign invaders.

Conclusion

  • This session will continue covering details about the lymphatic system during the next class.