Thyroid Histology: Simple Cuboidal Epithelium Lining the Follicles

Structure

The thyroid gland consists of numerous spherical follicles filled with colloid (thyroglobulin). Each follicle is lined by a single layer of simple cuboidal epithelium (thyrocytes/follicular cells).

Cellular Features

• Shape: Cube-shaped (height ≈ width) when inactive; become columnar when stimulated (TSH).
• Nucleus: Large, round, centrally located.
• Apical Surface: Microvilli project into colloid for endocytosis/exocytosis.
• Basal Surface: Rest on basal lamina; rich capillary network for hormone secretion.

Function

• Synthesis: Iodide uptake (NIS), oxidation (TPO), organification (coupling) on thyroglobulin.
• Storage: Colloid = thyroglobulin + iodinated tyrosines.
• Secretion: TSH → endocytosis of colloid → lysosomal proteolysis → T3/T4 release into capillaries.

Other Locations of Simple Cuboidal Epithelium

• Kidney: Proximal/distal convoluted tubules, collecting ducts (absorption/secretion).
• Pancreas: Ductal epithelium.
• Salivary glands: Ducts (intercalated, striated).
• Ovary: Surface epithelium (germinal epithelium).
• Choroid plexus: CSF production.
• Lens epithelium (anterior).