HIstology of Thyroid & Parathyroid glands Flashcards
Where is the thyroid gland located?
Located in the neck, anterior to the trachea, below the larynx.
What are the gross structures of the thyroid gland?
Consists of two lobes (right and left) connected by an isthmus.
What is the primary function of the thyroid gland?
Produces hormones (T3, T4) that regulate metabolism, growth, and development.
What are the key components of thyroid histology?
Capsule, septa, lobules, thyroid follicles, follicular cells, and parafollicular (C) cells.
What is unique about thyroid hormone storage?
It stores hormones extracellularly in large quantities as colloid within follicles.
What do follicular cells produce?
They produce thyroglobulin and thyroid hormones (T3, T4).
What is the function of parafollicular (C) cells?
Secrete calcitonin, which lowers blood calcium levels.
What is the structure of a thyroid follicle?
Spherical structure lined by cuboidal follicular cells, filled with colloid (thyroglobulin).
VWhat is stored in the colloid of thyroid follicles?
Thyroglobulin, a precursor for thyroid hormones.
How do inactive and active follicles differ?
Active follicles have reabsorption lacunae in the colloid due to hormone secretion.
What is the role of the Na+/I- symporter (NIS) in thyroid cells?
Transports iodide into follicular cells for hormone synthesis.
How are T3 and T4 formed?
Iodination of tyrosine residues in thyroglobulin (forming MIT, DIT), followed by coupling to create T3/T4.
What is the calorigenic effect of thyroid hormones?
Increases basal metabolic rate (BMR) and heat production.
Where are the parathyroid glands located?
Embedded on the posterior surface of the thyroid gland.
What are the two main cell types in the parathyroid?
Principal (chief) cells (secrete PTH) and oxyphil cells (function unclear).
What is the function of parathyroid hormone (PTH)?
Raises blood calcium levels by stimulating osteoclasts, increasing Ca2+ reabsorption, and activating vitamin D.
What causes a goiter?
Enlargement of the thyroid due to iodine deficiency or hyper/hypothyroidism.
What is the effect of defective parafollicular (C) cells?
Reduced calcitonin secretion, leading to impaired calcium homeostasis.
What diseases are associated with thyroid dysfunction?
Myxedema (hypothyroidism), Graves’ disease (hyperthyroidism), cretinism (developmental delay).
How do thyroid and parathyroid glands differ in function?
Thyroid regulates metabolism (T3/T4) and calcium (calcitonin); parathyroid regulates calcium (PTH).
What histological feature distinguishes thyroid follicles?
Colloid-filled lumen surrounded by follicular cells.
