The Thyroid Gland
The thyroid gland
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anatomic considerations
Formation and secretion of thyroid hormones
Transport and metabolism of thyroid hormones
Effects of thyroid hormones
Regulation of thyroid secretion
introduction: the thyroid gland
• The thyroid gland maintains the level of metabolism in the tissues that is optimal for their normal function.
• Thyroid hormones stimulate the O2 consumption of most of the cells in the body
• Thyroid hormones help regulate lipid and carbohydrate metabolism • Thyroid hormones are necessary for normal growth and maturation. introduction: the thyroid gland
• The absence of thyroid hormone causes mental and physical slowing, poor resistance to cold, and, in children, mental retardation and dwarfism.
• Excess thyroid secretion leads to body wasting, nervousness, tachycardia, tremor, and excess heat production.
• Thyroid function is controlled by the thyroid-stimulating hormone (TSH) of the anterior pituitary.
introduction: the thyroid gland
• The secretion of this tropic hormone is in turn regulated in part by thyrotropinreleasing hormone (TRH) from the hypothalamus and is subject to negative feedback control by high circulating levels of thyroid hormones acting on the anterior pituitary and the hypothalamus. Anatomic considerations
• The two lobes of the human thyroid are connected by a bridge of tissue, the thyroid isthmus, and there is sometimes a pyramidal lobe arising from the isthmus in front of the larynx
• The gland is well vascularized, and the thyroid has one of the highest rates of blood flow per gram of tissue of any organ in the body.
Anatomic considerations
• The thyroid is made up of multiple acini (follicles).
• Each spherical follicle is surrounded by a single layer of cells and filled with pink-staining proteinaceous material called colloid.
Anatomic considerations
• When the gland is inactive, the colloid is abundant, the follicles are large, and the cells lining them are flat. • When the gland is active,
•
•
•
•
•
anatomic considerations
Formation and secretion of thyroid hormones
Transport and metabolism of thyroid hormones
Effects of thyroid hormones
Regulation of thyroid secretion
introduction: the thyroid gland
• The thyroid gland maintains the level of metabolism in the tissues that is optimal for their normal function.
• Thyroid hormones stimulate the O2 consumption of most of the cells in the body
• Thyroid hormones help regulate lipid and carbohydrate metabolism • Thyroid hormones are necessary for normal growth and maturation. introduction: the thyroid gland
• The absence of thyroid hormone causes mental and physical slowing, poor resistance to cold, and, in children, mental retardation and dwarfism.
• Excess thyroid secretion leads to body wasting, nervousness, tachycardia, tremor, and excess heat production.
• Thyroid function is controlled by the thyroid-stimulating hormone (TSH) of the anterior pituitary.
introduction: the thyroid gland
• The secretion of this tropic hormone is in turn regulated in part by thyrotropinreleasing hormone (TRH) from the hypothalamus and is subject to negative feedback control by high circulating levels of thyroid hormones acting on the anterior pituitary and the hypothalamus. Anatomic considerations
• The two lobes of the human thyroid are connected by a bridge of tissue, the thyroid isthmus, and there is sometimes a pyramidal lobe arising from the isthmus in front of the larynx
• The gland is well vascularized, and the thyroid has one of the highest rates of blood flow per gram of tissue of any organ in the body.
Anatomic considerations
• The thyroid is made up of multiple acini (follicles).
• Each spherical follicle is surrounded by a single layer of cells and filled with pink-staining proteinaceous material called colloid.
Anatomic considerations
• When the gland is inactive, the colloid is abundant, the follicles are large, and the cells lining them are flat. • When the gland is active,