Spleen Histology: Key Concepts

Overview of the Lymphatic System

• Part of the immune system consisting of lymphatic vessels, tissues, and organs.
• Lymphatic vessels drain interstitial fluid or lymph from peripheral tissues into the blood.
• Lymphoid tissues and organs are rich in lymphocytes and other white blood cells.

Primary and Secondary Lymphoid Organs

• Primary Lymphoid Organs: Thymus and bone marrow.
• Secondary Lymphoid Organs: Tonsils, lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT).

The Spleen

• Largest lymphoid organ.
• Receives blood from the splenic artery.
• Primarily filters blood, unlike other lymphoid organs which filter lymph.
• Encapsulated organ, typically 12 cm in length, 7 cm wide, and 3 cm deep.

Spleen Structure

• Parenchyma: Comprises red pulp with white nodules of lymphatic tissue known as white pulp.
• Histology:
  • Red pulp stains pink and purple; white pulp stains dark purple due to numerous basophilic nuclei.
  • Capsule: Dense pink connective tissue surrounding the spleen.
  • Trabeculae: Extensions of connective tissue into the spleen, occasionally surrounding arteries.

White and Red Pulp

• White Pulp:

  • Consists mainly of T cells and B cells.
  • Contains spherical nodules known as splenic nodules.
  • Periarteriolar lymphoid sheath (PALS) surrounds central arterioles, mainly composed of T cells.

• Red Pulp:

  • Highly vascular tissue.
  • Plays a role in removing old and damaged red blood cells.

Immune Function

• The spleen filters blood and removes damaged or old red blood cells.
• White Pulp:
  • Arranged in nodules called splenic nodules, involved in immune functions.
  • Contains follicles (B-lymphocytes) and marginal zone (mix of B- and T-lymphocytes and macrophages).

Conclusion

• The spleen is crucial for immune responses and blood filtration.
• Important in understanding how the immune system functions and the role of lymphoid organs in health and disease.