Cells in Lymph and the thymus

Examine the blood smear slide (10) again, focusing attention only on the structure of the lymphocytes of different sizes.

What technique could you use to distinguish T and B lymphocytes on a slide?

What are the respective functions of T lymphocytes and B lymphocytes?

Thymus

Examine a section of thymus (slide 126), noting

• The capsule,
• Septa, and
• The organization of lobes into a basophilic cortex and eosinophilic medulla (Fig. 14-10).

Identify the epithelial-reticular cells or epitheliocytes (Fig. 14-11) which make up the framework of the thymus.

• These are larger and paler than the lymphocytes. In the medulla, identify the masses of epithelial cells, thymic or Hassal's corpuscles (Fig. 14-10 and 14-12 ).

Examine also a section of involuted thymus (slide 123) and note the fatty infiltration and lymphocyte depletion.

What are three functions of thymic epithelial cells?

Identify macrophages in the thymic cortex (they are typically larger and more pale than lymphocytes and less numerous than the epithelial-reticular cells) and look for mitotic figures among the lymphocytes of this region.

What are some functional differences between lymphocytes in the thymic medulla and cortex?

Next let's look at a lymph node.