Slide DMS160, [Thyroid, monkey, PTS]. This slide of plastic-embedded tissue shows some cytological details better than the previous slide. Look for the same general features as described above. You may see a small part of an associated parathyoid gland in your section. Parafollicular ("C") cells may occur singly among the follicular epithelial cells, inside the follicular basal lamina but not making contact with the colloid, or in clusters outside the follicles, but their positive identification requires immunocytochemical techniques. What hormone do these cells secrete and what are its physiological effects?

Comparison of inactive and active thyroid follicles: 1. Colloid (e.g., thyroglobulin); 2. Squamous follicule cells; 3. Resorption lacunae; 4. Columnar follicle cells