Question

Thyroid regulation of Cellular Metabolism Describe the microscopic organization and function of the thyroid Compare and contrast the endocrine activity of thyroid hormone The thyroid and parathyroid maintain blood calcium homeostasis Describe the endocrine function of each hormone on bone synthesis and blood calcium levels Parathyroid glands are embedded within the posterior thyroid gland Secretes Parathyroid hormone (Parathormone, PTH). PTH action also induces calcitriol secretion

Answer 1

microscopic organisation and function of thyroid gland:

1. Thyroid follicle: responsible for production and secretion of thyroxine or T4 and triodothyronine T3.

Function: regulates body's temperature, metabolism and heart rate.

2.colloid; Thyroid nodules can be solid if they are comprised of thyroid or other cells or an accumulation of stored thyroid hormone called colloid . When nodules contain fluid, they are called cystic nodules. and can be completly filled with fluid or partly filled and parly solid also. they may be smll or larger may be benign or malignant.

3. follicular cells: tThese are small globular sacs lining the lobes ,isthmus and contain enzymes needed to synthesize thyroglobulin, as well as the enzymes needed to release thyroid hormone from thyroglobulin  When thyroid hormones are needed, thyroglobulin is reabsorbed from the colloid in the follicular lumen into the cells, where it is split into its component parts, including the two thyroid hormones T₄ and T₃. The hormones are then released, passing from the cells into the circulation.

4 para follicular cells: Also called C cells and are neurendocrine cells in the thyroid gland whose primary function is to secrete calcitonin .They are located adjacent to the thyroid follicles and reside in the connective tissue.

ENDOCRINE activity of thyroid hormones comparison:

INACTIVE hormone secreted by Thyroid:Thyroxine is the main hormone secreted into the bloodstream by the thyroid gland.

The production of this hormone system is regulated by a negative feedback loop so that when the levels of the thyroid hormones, thyroxine and triiodothyronine increase, they prevent the release of both thyrotropin-releasing hormone and thyroid stimulating hormone orTSH. This system allows the body to maintain a constant level of thyroid hormones in the body.

The release of too much thyroxine in the bloodstream is known as thyrotoxicosis.

T₃ and T4 : It is important that T3 and T4 levels are neither too high nor too low. Two glands in the brain—the hypothalamus and the pituitary communicate to maintain T3 and T4 balance.The hormones regulate the speed with which the metabolism work. any increase or decrease may lead to hyper and hypo thyroidism respectively.

Para thyroid glands secrete parathyroid hormone or the PTH and takes part in the control of calcium and phosphate homeostasis as well asthe bone physiology.

Calcitonin is a hormone produced by the parafollicular cells and is involved in regulting the levels of calcium and phosphate in the blood opposing the action of the parathyroid hormone.