Biology 202: Lab 6 - The Lymphatic System and Immune Response

Introduction

• Focus on Lab Exercise 35 (Page 519-526 in lab manual).
• Emphasis on key points already covered in lectures.
• Newly added lab; shorter than others.

The Lymphatic System

• Components:

  • Network of lymphatic vessels (lymphatics), lymphoid tissue, lymph nodes, lymphoid organs (tonsils, thymus, spleen).

• Function in Circulatory System:

  • Fluid leaves capillaries at arterial end, returns at venous end.
  • Excess fluid collected by lymphatic capillaries, transported via larger vessels and trunks.
  • Lymph returns to bloodstream through two main ducts:
    • Right Lymph Duct: Drains right upper extremity, head, and thorax.
    • Thoracic Duct: Drains the rest of the body, located at the cisterna chyli.

• Lymph Nodes:

  • Bean-shaped structures filtering lymph.
  • Embedded in connective tissue, widespread throughout the body.
  • Large collections in inguinal (upper thigh/hip), axillary (armpit), and cervical (neck) regions.

• Lymphoid Organs:

  • Primary: Thymus, red bone marrow.
  • Secondary: Tonsils, spleen, Peyer's patches, appendix.

The Immune Response

• Defense Mechanisms:

  • Innate (Non-specific):

    • Surface barriers (skin, mucous membranes).
    • Fast-acting internal defenses (phagocytes, inflammation, fever).
    • No memory of pathogens.

  • Adaptive (Specific):

    • Develops over time; immunological memory.
    • Specific to pathogens (B and T cells).
    • Builds antibodies for specific pathogens.

• Adaptive Immune Response Characteristics:

  1. Memory: Remembers past infections for faster response.
  2. Specificity: Responds to specific antigens.
  3. Self-tolerance: Differentiates self from foreign invaders.

B Cells and T Cells

• B Cells (B Lymphocytes):

  • Attack invaders outside cells.
  • Originate and mature in red bone marrow.
  • Part of humoral (antibody-mediated) immunity.

• T Cells (T Lymphocytes):

  • Attack infected cells.
  • Originate in red bone marrow, mature in thymus.
  • Part of cell-mediated immunity.

• Comparison:

  • B Lymphocytes:

    • Produce antibodies that circulate in blood.
    • Plasma cells secrete specific antibodies.

  • T Lymphocytes:

    • Cytotoxic T cells, helper T cells, regulatory T cells.
    • Direct attack without antibodies.

Antibody Production

• B cells differentiate into plasma cells upon encountering matching antigens.
• Antibody Types (Mnemonic: GAMED):
  • IgG: Most abundant, crosses placenta.
  • IgA: Found in mucous membranes, breast milk, saliva, tears.
  • IgM: First antibody made, largest.
  • IgE: Involved in allergies.
  • IgD: Function largely unknown.

Conclusion

• Complete all questions in Exercise 35 (1-22).
• Watch additional lab videos and complete review sheets.
• Prepare for module/unit exam.