Stanley_Hall_7

Blood Cell Formation

• Blood cell formation, also known as hematopoiesis, occurs in specific locations within the body, primarily in the bone marrow.

• Blood cells are pushed through large fenestrations in the bone marrow, allowing them to enter the bloodstream.

• Sinusoids: These are specialized capillaries within the bone marrow with larger openings that facilitate the passage of blood cells into circulation.

Lifespan of Blood Cells

• The lifespan of white blood cells (leukocytes) can vary:

  • Shorter lifespan: Associated with active participation in the immune response during an infection.

  • Longer lifespan: Occurs when there is no active infection.

• If the leukocyte count drops, the red bone marrow is triggered to produce more through hormonal signaling, maintaining levels as needed.

  • Typical lifespan is around 20 days for leukocytes under normal conditions.

The Thymus Gland

• Structure:

  • Surrounded by a fibrous capsule that extends into the gland via invaginations called trabeculae, dividing it into lobes.

  • Contains cortex (outer layer) and medulla (inner layer); the cortex is where lymphocytes arrive and migrate for maturation.

• Degeneration and Dilution: The thymus decreases in size with age, but lymphocytes migrate to loading areas and continue maturing.

Lymph Nodes

• Location and Function: Lymph nodes are distributed throughout the body and serve as sites of T and B cell activation, responding to foreign antigens.

• Structure:

  • Contains reticular fibers and reticular cells forming a network for structural support within the lymph node.

  • The main structure is divided into cortex and medulla with follicles in the cortex, containing germinal centers for B cell maturation into plasma cells.

Lymphadenitis and Lymphadenopathy

• Lymphadenitis: Swelling of lymph nodes due to infection, often felt in the cervical region during throat infections.

• Lymphadenopathy: A general term for diseases affecting lymph nodes, indicating potential issues such as infections or malignancies.

Immunity Overview

• Innate Immunity: First line of defense with rapid response systems:

  • Includes dendritic cells in the skin, natural killer cells, macrophages, and neutrophils.

  • Serves to handle pathogens quickly before they spread deeper into the body.

• Adaptive Immunity: Activated once innate defenses are breached:

  • Specific response from B cells producing antibodies tailored to specific pathogens.

  • Works in conjunction with innate immunity to provide a comprehensive defense system against infections.

Conclusion

• Understanding the processes behind blood cell formation, the role of the thymus and lymph nodes, and the distinction between innate and adaptive immunity is critical in comprehending the immune system's response to pathogens.