Endocrine II - Thyroid, Parathyroid, and Adrenal Glands Flashcards
What is the thyroid gland derived from?
A downgrowth of oral epithelium from the base of the tongue
What type of cells line thyroid lobules?
Follicular cells are simple cuboidal
What are thyroid follicle lumens filled with?
Colloid
What is colloid made from?
Thyroglobulin - a precursor of thyroid hormone.
What are the basic steps in thyroid hormone synthesis?
- Thyroglobulin is made by follicular cell and exocytosed into colloid
- Conjugation in the colloid produces triiodothyronine and tetraiodothyronine residues bound to thyroglobulin
- Cell endocytoses colloid, bringing in the hormone precursors.
- Endosomal acidification results in proteolytic cleavage, releasing T3 and T4.
Which thyroid hormone is most potent?
T3
Where are parafollicular cells found? What do they do?
They are found deep to the follicular epithelium of the thyroid lobules and they secrete calcitonin.
What does calcitonin do?
Lowers blood calcium levels by lowering osteoclast activity and lowering calcium absorption.
How do parafollicular cells stain?
Pale-staining. Calcitonin granules can be seen with EM.
Where are the parathyroid glands located?
Posterior surface of the thyroid.
What two cell types are found in the parathyroid gland? Which one is most abundant?
Chief cells and oxyphil cells. Chief cells most abundant.
What do chief cells of the parathyroid do?
Produce parathyroid hormone (PTH)
What is a histological feature of parathyroid chief cells?
Dark, centrally-located nuclei, small cytoplasm, tightly packed together.
What does parathyroid hormone (PTH) do?
Raises calcium levels by increasing osteoclast activity and stimulating vitamin D activation in the kidney. Vitamin D increases calcium absorption in the GI tract.
PTH and calcitonin are antagonists to each other, but only one is essential. Which one is it?
PTH