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
What do parathyroid oxyphil cells look like histologically?
Pale, large cytoplasm surrounding dark, centrally-located nuclei. They look like fried eggs. They exist in clumps.
Where are the adrenal glands located?
Superior to the kidneys.
What structure surrounds the adrenal glands?
A thick CT capsule (with trabeculae)
What is the main function of the adrenal cortex?
Steroid hormone production
What is the main function of the adrenal medulla?
Catecholamine production
What are catecholamines derived from?
Tyrosine
What controls the adrenal cortex?
Angiotensin II and ACTH
What is the adrenal medulla controlled by?
Sympathetic fibers and adrenal cortex hormones
What are the three zones of the adrenal cortex?
Outer: Zona glomerulosa, middle: zona fasciculata, inner: zona reticularis
What do zona glomerulosa cells do? How are they arranged?
They make mineralocorticoids like aldosterone. Cells are found in clumps.
Note: Mineralocorticoids are so named because they are steroid hormones that regulate salt balance (mineral balance).
Which adrenal cortex zone is the widest?
Zona fasciculata
What is produced in the zona fasciculata?
Glucocorticoids like cortisol and sex steroids.
Note: Glucocorticoids are steroid hornomes that regulate carbohydrate metabolism.
What is made in the zona reticularis?
Androgens mainly
What is the main cell type found in the adrenal medulla?
Chromaffin cells.
What are chromaffin cells derived from?
Neural crest
What are the two types of chromaffin cells?
E cells and NE cells.
What do E cells and NE cells do?
E cells make, store, and release epinephrine.
NE cells make, store and release norepinephrine.
What is special about the blood supply in the adrenal gland?
Some arteries feed the cortex first, then re-join to go to the medulla. This allows glucocorticoids made in the cortex to exert their effects on the medulla.
What controls the zona glomerulosa? What controls the zona fasciculata?
Angiotensin II controls glomerulosa. ACTH controls the fasciculata.
What is the adrenal medulla derived from?
Neural crest.
