Lecture Notes: Chapter 22, Lecture 2 - Lymphatic Organs and Tissues

Overview of Lymphatic System

• Lymphatic organs and tissues are distributed throughout the body.
• Primary Lymphatic Organs: Sites where stem cells divide and mature into B and T lymphocytes.
  • Red Bone Marrow: Produces mature B cells.
  • Thymus: Maturation site for pre-T cells from red marrow.
• Secondary Lymphatic Organs and Tissues: Sites of most immune responses.
  • Includes lymph nodes, spleen, and lymphatic nodules.

General Anatomy Terms

• Capsule: Outermost layer of most organs, made of connective tissue, provides protection.
• Cortex and Medulla:
  • Cortex: Outer part, deep to the capsule.
  • Medulla: Inner part.
• Stroma and Parenchyma:
  • Stroma: Structural part of an organ (analogous to a building).
  • Parenchyma: Functional part of an organ (analogous to people working in a building).
• Hilum (Hilus): Area where blood vessels, lymphatics, and nerves enter/exit an organ (e.g., lungs, kidneys).
• Afferent and Efferent:
  • Afferent: Going towards something (e.g., lymph entering lymph nodes).
  • Efferent: Going away from something (e.g., lymph exiting lymph nodes).

Thymus Gland

• Located in the mediastinum, has two lobes.
• Larger in infants; atrophies in adults.
• Structure:
  • Capsule: Protective outer covering.
  • Trabeculae: Extensions of the capsule dividing the thymus into lobules.
  • Lobules:
    • Cortex: Packed with lymphocytes and macrophages.
    • Medulla: Contains reticular epithelial cells, produces hormones and Hassall's corpuscles.
• Importance:
  • Site for T cell maturation, crucial during infancy for developing specific immunity.

Lymph Nodes

• Resemble kidney beans and are encapsulated.
• Located along lymphatic vessels.
• Contain T-cells, macrophages, dendritic cells, and B cells.
• Function:
  • Lymph enters via afferent vessels, filtered for pathogens.
  • Immune response mounted by macrophages (phagocytosis) and lymphocytes (immune response).
  • Lymph exits via efferent vessels.
  • Site of proliferation for plasma cells (mature B cells) and T cells.
• Clinical Significance:
  • Swelling of lymph nodes (e.g., during infection) is due to rapid cell proliferation.
  • Location and flow of lymph are key in diagnosing/prognosing cancer spread.
  • Examples: Axillary lymph nodes in breast cancer metastasis.

Cancer and Lymphatic System

• Malignant tumors can spread through lymphatic or cardiovascular systems.
• Diagnosis and Prognosis:
  • Biopsy of lymph nodes (e.g., axillary nodes) can indicate cancer spread.
  • Removal of lymph nodes can cause permanent swelling due to impaired lymph drainage.
• Differentiation:
  • Cancerous lymph nodes: Firm, enlarged, non-tender.
  • Infected lymph nodes: Squishy and sore.
  • Note: Not all firm lymph nodes indicate cancer; professional evaluation is necessary.

These notes provide an overview and key details about the lymphatic organs and tissues, their functions, and their clinical significance, particularly in relation to the immune system and cancer spread.