Các tuyến giáp của con người bao gồm hai thùy thuộc hai bên của khí quản bằng mô liên kết. Hai thùy được kết nối bởi một ban nhạc của mô tuyến giáp hoặc eo đất, nằm ngay bên dưới sụn cricoid. Một tuyến giáp bình thường trong một người lớn khỏe mạnh nặng khoảng 20 g. | CHAPTER 33 The Thyroid Gland 597 carry out their physiological functions. The thyroid hormones exert their regulatory functions by influencing gene expression affecting the developmental program and the amount of cellular constituents needed for the normal rate of metabolism. FUNCTIONAL ANATOMY OF THE THYROID GLAND The human thyroid gland consists of two lobes attached to either side of the trachea by connective tissue. The two lobes are connected by a band of thyroid tissue or isthmus which lies just below the cricoid cartilage. A normal thyroid gland in a healthy adult weighs about 20 g. Each lobe of the thyroid receives its arterial blood supply from a superior and an inferior thyroid artery which arise from the external carotid and subclavian artery respectively. Blood leaves the lobes of the thyroid by a series of thyroid veins that drain into the external jugular and innominate veins. This circulation provides a rich blood supply to the thyroid gland giving it a higher rate of blood flow per gram than even that of the kidneys. The thyroid gland receives adrenergic innervation from the cervical ganglia and cholinergic innervation from the vagus nerves. This innervation regulates vasomotor function to increase the delivery of TSH iodide and metabolic substrates to the thyroid gland. The adrenergic system can also affect thyroid function by direct effects on the cells. Thyroxine and Triiodothyronine Are Synthesized and Secreted by the Thyroid Follicle The lobes of the thyroid gland consist of aggregates of many spherical follicles lined by a single layer of epithelial cells Fig. . The apical membranes of the follicular Follicular cell Colloid Capillary Parafollicular cell FIGURE .A cross-sectional view through a portion of the human thyroid gland. cells which face the lumen are covered with microvilli. Pseudopods formed from the apical membrane extend into the lumen. The lateral membranes of the follicular cells are connected by tight junctions which .
