Tiroida

Tiroida, known in English as the thyroid gland, is a butterfly-shaped endocrine gland located in the anterior neck. It has two lobes separated by an isthmus and is enclosed by a capsule. Thyroid follicles contain colloid; follicular cells synthesize thyroid hormones while parafollicular cells secrete calcitonin.

The main hormones are thyroxine (T4) and triiodothyronine (T3). They regulate metabolism, growth, and development, and influence body temperature and heart rate. Calcitonin helps regulate calcium balance, though its role is less central than that of parathyroid hormone.

Iodine uptake is essential for hormone production; iodine is stored in colloid and incorporated into T3 and T4.

Regulation occurs via the hypothalamic-pituitary-thyroid axis. The hypothalamus releases TRH, prompting the pituitary to secrete TSH, which stimulates thyroid hormone synthesis and release. T3 and T4 provide negative feedback to both hypothalamus and pituitary.

Anatomy and blood supply: the thyroid receives blood from the superior and inferior thyroid arteries and drains to the internal jugular veins. Innervation comes from branches of the vagus nerve, including the recurrent laryngeal nerve.

Development: the gland originates from the floor of the pharynx during embryogenesis and matures in the perinatal period.

Clinical relevance: common disorders include hypothyroidism, hyperthyroidism, goiter, nodules, and thyroid cancer. Newborn screening can detect congenital hypothyroidism in many countries.

Diagnosis and treatment: evaluation typically includes serum TSH and free T4, with antibodies as needed; imaging by ultrasound; radioactive iodine uptake tests; and fine-needle aspiration for suspicious nodules. Treatment varies by condition: levothyroxine for hypothyroidism; antithyroid drugs or radioactive iodine for hyperthyroidism; and surgery for cancer or large goiters.