Exam 5 Review:  Chapter 16:  Thyroid-Parathyroid Glands

thyroid follicles - the structural subunit of the thyroid gland, consisting of a roughly spherical mass of thyroid colloid composed of thyroglobulin, the inactive storage form for the thyroid hormones, surounded by a layer of simple cuboidal glandular epithelium composed of follicular cells which synthesize, store, and release the thyroid hormones, thyroxine = tetraiodothyronine = T₄ and triiodothyronine = T_3.

thyroid colloid = thyroglobulin - The gelatinous amorphous material which fills thyroid follicles consisting of the large inactive storage protein from which thyroid follicular cells can extract active thyroid hormones, thyroxine = tetraiodothyronine = T₄ and triiodothyronine = T_3.

thyroid hormones - (1) amines:  thyroxine = tetraiodothyronine = T₄ and triiodothyronine = T₃ which are produced by follicular cells in response to TSH and target most cells in the body to increase their cellular metabolism, a thermogenic effect; and (2) protein:  (thyro)calcitonin produced by the autoregulated parafollicular = C cells released in response to increases in plasma calcium ion levels which targets oseoblasts to increase formation of bone matrix causing a corresponding decrease in plasma calcium and phosphate ion levels.

thyroxine = tetraiodothyronine = T₄ - One of the two amine hormones, synthesized from two linked tyrosines, and containing four atoms of iodine, produced by follicular cells of the thyroid gland (in response to adenohypophyseal TSH) which targets most cells in the body to increase their cellular metabolism, a thermogenic effect.

triiodothyronine = T₃ - One of the two amine hormones, synthesized from two linked tyrosines, and containing three atoms of iodine, produced by follicular cells of the thyroid gland (in response to adenohypophyseal TSH) which targets most cells in the body to increase their cellular metabolism, a thermogenic effect.

iodine -A nonmetallic element of the halogen group required as a trace element, in humans primarily for the synthesis of thyroid hormones, T₃ and T₄ ; Symbol: I, Atomic number: 53.
 
calorigenic effect - The stimulation of body heat by increased metabolism by the thyroid hormones, thyroxine = tetraiodothyronine = T₄ and triiodothyronine = T_3.

parafollicular cell = C cell - The autoregulated endocrine cells found in the interstitial tissue between the thyroid follicles which synthesize and release (thyro)calcitonin in response to increases in plasma calcium ion levels.

calcitonin = thyrocalcitonin - A protein hormone, produced by the parafollicular cells/C cells of the thyroid gland which lowers plasma calcium and phosphate levels by targeting oseoblasts to increase formation of bone matrix; the antagonist to parathyroid hormone.

parathyroid hormone = parathormone = PTH - A protein hormone, produced by the principle or chief cells of the parathyroid gland which increases plasma calcium levels (mechanisms 1, 2, and 3) and decreases plasma phosphate levels (mechanism 3) by (1) targeting oseoclasts to increase dissolution of bone matrix, (2) targeting the intestinal lining to increase calcium ion absorption from the digested meal, and (3) targeting the kidney to reaabsorb calcium ions from and secrete phosphate ions into the urine; PTH is the antagonist to thyrocalcitonine.

vitamin D - A fat-soluble vitamin occurring in several forms, especially vitamin D₂ or vitamin D₃, required for normal growth of teeth and bones, and produced in general by ultraviolet irradiation of sterols found in milk, fish, and eggs; rickets develops with severe dietary deficiency.

vitamin D₃= calcitriol - The activated form of vitamin D, activated in response to parathormone action, which is necessary for adequate calcium absorption from food in the intestines.

Sketch and label:

2.  the thyroid gland at the cellular level.

6. a negative feedback pathway for the regulation of:

      b.  Thyroid Hormones