BSI 2 Lecture 49: Endocrine 3 Flashcards
What major hormones does the thyroid gland secrete?
T3, T4, and Calcitonin
What cells in the thyroid secrete triiodothyronine and thyroxine?
Follicular cells
What cells in the thyroid secrete Calcitonin?
Parafollicular cells (C cells)
What are the thyroid hormones T3 and T4 responsible for?
Basal metabolic rate
What controls secretion of thyroid hormones?
Thyroid releasing hormone and somatostatin secreted by the hypothalamus and then thyroid stimulating hormone secreted by the anterior pituitary
What does TSH do to the follicular cells in the thyroid?
It increases proteolysis of thyroglobulin, it increases activity of the iodide pump, increases iodination of thyroglobulin, and increases number, size, and activity of thyroid follicular cells
What is the thyroid gland composed of?
Cuboidal epithelial cells formed into round follicles which contain a colloid composed of the T3 and T4 hormones with scattered C cells
Describe the process of synthesizing T3 and T4
1) Thyroglobulin gets synthesized in the follicle cell and is transported to the lumen
2) Sodium and Iodide are co-transported into the follicle cell where iodide is moved into the lumen
3) Iodide can attach to either one place (MIT) or two places (DIT) on the thyroglobulin.
4) DIT + MIT = T3 and DIT + DIT = T4
5) The thyroglobulin and T3/T4 complex leaves the lumen by endocytosis into the follicle cell
6) Lysosomal enzymes split and release T3 and T4
7) Amino acid residues are reused to make thyroglobulin
What percentage of the secretions of the thyroid gland is T4?
~93%
What happens to most of the T4 in tissues?
It is converted to T3
Which one is stronger, T3 or T4?
T3
Which one has a shorter half life, T3 or T4?
T3
How much iodinated thyroglobulin can the thyroid store?
About a 2-3 month supply
How are the thyroid hormones transported?
Bound to plasma proteins (Thyroxine-binding globulin)
What does the parathyroid release?
PTH
