The Thyroid Gland
The thyroid is a butterfly-shaped endocrine gland located anterior to the trachea, responsible for regulating metabolism via the production of thyroid hormones (T3/T4) and calcium homeostasis (calcitonin).
Microscopic Organization
| Cell Type | Function |
|---|---|
| Follicular Cells | Simple cuboidal/columnar cells that synthesize T3/T4 are stored in the colloid. |
| Parafollicular (C) Cells | Located within the follicular basement membrane; secrete calcitonin. |
Hormone Physiology
- Thyroid Follicles: The functional unit. Contain colloid (thyroglobulin), the precursor for T3 and T4.
- Regulation: TSH (from the anterior pituitary) binds to receptors on follicular cells to stimulate uptake of iodide and release of hormones.
- Calcitonin: Lowers serum calcium by inhibiting osteoclast activity in bone.
High-Yield Exam Pearl:
Medullary Thyroid Carcinoma originates from the neuroendocrine Parafollicular (C) cells. It is a hallmark of MEN 2A and 2B syndromes and is characterized by amyloid deposits on histology due to calcitonin production.