Fig. 2

Photomicrograph of sections in the thyroid gland of an albino rat from: a Control group demonstrating several thyroid follicles (F) of variable diameters, lined with simple cubical epithelial cells, follicular cells (arrows), exhibiting central rounded vesicular nuclei and basophilic cytoplasm. Follicles are filled with homogenous eosinophilic colloid (C) revealing peripheral endocytic vacuoles (E). Interfollicular tissue is formed of thin connective tissue with blood capillaries (B). Parafollicular cells (dashed arrow) are larger and paler than the lining follicular cells and do not reach the lumina of the follicles. b, c Both hypothyroidism (b) and recovery (c) groups are showing enlarged follicles (F) either partially or entirely devoid of colloid (asterisk) or exhibiting large endocytic vacuoles (E). Follicles are lined mainly with flat follicular cells with flattened nuclei (curved arrows). Some cells were cubical and ballooned with vacuolated cytoplasm and rounded dark nuclei (wavy arrow). Distorted follicles (D) with sequestration of some follicular cells from the basement membrane are also noted. d Thyroxin-treated group. Most of the thyroid follicles (F) are apparently normal, lined with simple cubical epithelial cells having central rounded vesicular nuclei (arrows) and parafollicular cells (dashed  arrows). Follicles have an eosinophilic colloid (C) exhibiting several endocytic vacuoles (E). Few follicular cells with dark nuclei and vacuolated cytoplasm are noted (wavy  arrows). [H&E, × 400]