Calcium Hormones

Parathyroid Glands

The prefix “para” means “to the side.” These purple bumps or zits you see on the thyroid are the parathyroid organs. They’re located on the posterior aspect of the thyroid, and there are four parathyroid organs. In lab, when viewing slides of the parathyroid glandSmall glands on the thyroid that secrete PTH to regulate calcium., you will see the characteristic tissues of the thyroid gland Endocrine gland regulating metabolism through thyroid hormones.. They surround a big purple blotch.  One of these parathyroid glands is that purple blotch.

The parathyroid gland has two cell types: principal cellsThe basic structural and functional units of life. (formerly called chief cells) and oxyphil cells. The chief cells stain dark purple in the nucleusThe control center of the cell that contains DNA and directs cellular activities.. They stain light purple in the cytoplasmThe gel-like substance within a cell that contains organelles and cytosol.. Oxyphil cells have a pinkish cytoplasm.  Principle cells make the parathyroid hormone(PTH): Raises blood calcium by stimulating bone resorption. in response to high calcium levels in the blood.  The parathyroid gland is both sensor and control centerThe part of a feedback loop that processes information and initiates a response. in this feedback loop.  Because PTH is release in response to blood levels, this is a humoral trigger.

Thyroid Microanatomy

Recall from another rminilecture on the thyroid that the thyroid consists of all these folliclesStructures in the ovaries that contain developing oocytes.: colloidA mixture where small particles are dispersed but not dissolved in a liquid. surrounded by follicular cellsCells surrounding the oocyte that support its development..  Between the follicles are the appropriately named C cells.  C cells in the thyroid gland produce calcitoninA hormone from the thyroid that lowers blood calcium levels by inhibiting osteoclasts., a hormone that lowers blood calcium levels.

BOTH Hormones

Both PTH and calcitonin are released in respond to blood calcium levels, giving them both humoral triggers.  Both hormones affect the same three organs: kidney, small intestine, and bone.  However, they have opposite effects.  PTH’s purpose is to raise blood calcium.  It affects the entryway for calcium, your small intestine. This allows it to take in more from your food. This process is called absorption.  PTH affects your kidney, the exit for calcium, to retain more calcium in a process called reabsorptionThe process of fluid moving back into capillaries from surrounding tissues due to colloid osmotic pr.  PTH affects bone, but we know that there are a bunch of different cells in bone.  PTH specifically affects osteoclasts to increase bone breakdown or osteolysis.  By releasing calcium, this will raise the calcium levels in blood.

Calcitonin lowers absorption in the small intestine. It also decreases reabsorption in the kidney. Instead of affecting osteoclasts, calcitonin targets osteoblasts. It facilitates the uptake of calcium from the blood. This process preserves calcium in the bone’s calcium matrix. 

Antagonistic Hormones

Antagonistic hormones like calcitonin and PTH work in opposition.  Insulin and glucagonIncreases blood sugar by promoting glycogen breakdown. from the pancreasA gland that produces digestive enzymes and hormones like insulin and glucagon. do the same for blood glucoseA simple sugar that is the main source of energy for cells..  Insulin lowers it while glucagon increases it.  Antagonistic hormones work against each other.  But, what about when hormones work with each other?  This is called permissiveness and is seen in the thyroid gland.  When thyroid hormone (TH): Includes T3 and T4, regulating metabolism. is really high, it inserts epinephrineadrenaline): Fight-or-flight hormone from the adrenal medulla. receptorsProteins located on the surface or inside cells that bind specific molecules (e.g., neurotransmitter into cardiac muscle fibers.  So you get a double dose of heart rate increase from TH AND from epinephrine..