Thyroid and Parathyroid Gland Function The thyroid and parathyroid glands are key regulators within the endocrine system. Located in the anterior neck, these glands play essential roles in metabolic control and calcium homeostasis. Their hormones exert widespread systemic effects, influencing energy balance, skeletal integrity, and neuromuscular function. Thyroid Hormones and Metabolic Regulation The thyroid gland produces triiodothyronine (T3) and thyroxine (T4), hormones that regulate basal metabolic rate and cellular energy utilisation. Thyroid hormones influence gluconeogenesis, glycogenolysis, lipogenesis, protein synthesis, and thermogenesis. Their secretion is tightly controlled by the hypothalamic–pituitary–thyroid axis, ensuring stable metabolic activity across tissues. Parathyroid Hormone and Calcium Balance The parathyroid glands regulate serum calcium through the secretion of parathyroid hormone (PTH). PTH acts on bone, kidneys, and indirectly on the gastrointestinal tract to maintain calcium and phosphate balance. Understanding thyroid and parathyroid physiology is fundamental for recognising disorders such as hyperthyroidism, hypothyroidism, and abnormalities of calcium regulation.