Thyroid glands and parathyroid gland.pptx

It gives detailed information about thyroid glands and parathyroid glands.

1. Thyroid Gland

2. The thyroid gland is situated in the neck in front of the lyranx and trachea at the level of the 5 th. 6 th and 7 th cervical and 1 st thoracic vertebrae. It resembles butterfly in shape, consisting of two lobes, one on either side of the thyroid cartilage and upper cartilaginous rings of the trachea. The lobes are joined by narrow isthmus, lying in front of trachea. The gland is composed of largely spherical follicles formed from cuboidal epithelium. These secrete and store colloid, a thick, sticky protein material. Between the follicles are parafollicular cells (sometimes called C-cells), found singly or in groups. They secrete the hormone calcitonin .

3. Synthesis and secretion of the thyroid Metabolic Hormones

4. The thyroid secretes two major hormones, thyroxine and triiodothyronine , commonly called T 4 and T 3 respectively. About 93 percent of the metabolically active hormones secreted by the thyroid gland is thyroxine , and 7 percent is triiodothyronine . Almost all the thyroxine is eventually convereted to triiodothyronine in the tissues, so both are functionally important. T3 is four times more potent than T4 but it is present in the blood in much less quantity

5. The thyroid gland also secrets calcitonin , a hormone involved in calcium metabolism

6. Physiological Functions of the Thyroid Hormones

7. Calcitonin This hormone is secreted by the parafollicular or C-cells in the thyroid gland. Calcitonin lowers blood calcium (Ca 2+ ) levels. It does this by acting on: Bone cells,promoting their storage of calcium Kidney tubules, inhibiting the reabsorption of calcium.

8. Parathyroid Glands There are four parathyroid glands, each weighing around 50 g; two are embedded in the posterior surface of each lobe of the thyroid glands. They are surrounded by fine connective tissue capsules that contain spherical cells arranged in columns, with sinusoids containing blood in between them.

9. Functions These glands secrete parathyroid hormone (PTH, also known as parathormone ), which regulates blood calcium levels.when these falls, secretion of PTH is increased and vice versa. PTH secretion increases blood calcium levels by releasing calcium stored in bone via a dual action: it stimulated osteoclasts (bone-destroying cells) and increases calcium reabsorption from the renal tubules.