Expansion
Thyroid follicles filled with colloid; parathyroid chief and oxyphil cells
Expansion
Thyroid
- Follicles lined by cuboidal epithelium and filled with colloid (thyroglobulin)
- The only endocrine gland storing hormone extracellularly, with reserves for 2 to 3 months
- Parafollicular (C) cells between follicles secrete calcitonin; of neural crest origin, and the cell of origin of medullary thyroid carcinoma
- Activity is reflected in appearance: active glands have tall columnar cells and scalloped colloid; inactive glands have flat cells and abundant dense colloid
Parathyroid
- Chief cells: small, pale, secrete parathyroid hormone
- Oxyphil cells: larger, eosinophilic, packed with mitochondria; function unclear, increase with age
- Embedded in fat, which increases with age
Diagnostic appearances worth knowing: Orphan Annie nuclei with clearing, nuclear grooves and psammoma bodies in papillary carcinoma; amyloid stroma in medullary carcinoma, derived from calcitonin; and lymphocytic infiltration with Hurthle cells in Hashimoto thyroiditis.