Skip to content

Regulation of Blood Calcium via PTH and Calcitonin

  • by

⚡ Welcome to Catalyst University! I am Kevin Tokoph, PT, DPT.

Welcome back to anatomy and physiology on catalyst university my name is kevin toke off please make sure to like this video and subscribe to my channel for future videos and notifications in this video we’re gonna talk about the negative feedback regulation of blood calcium levels and how that pertains to the activity of osteoclasts and osteoblasts okay so in

The previous two videos we looked at mainly the functions of osteoblasts in bone deposition so they increase bone mineral density and then the functions of osteoclasts in decreasing bone mineral density through the process of bone resorption okay now osteoclasts can kind of get a bad rap and that’s because if you just kind of think about it superficially they’re

Decreasing bone mineral density they’re degrading bone tissue and that seems like a bad thing and if it goes on prolonged it can cause osteoporosis yes but under normal conditions when someone’s not in danger of osteoporosis osteoclast activity is very important calcium levels in the blood need to be regulated very tightly because calcium is extremely important

Here’s just a few things that calcium is vital for blood clotting calcium actually it helps initiate the blood clotting cascade several the clotting factors which you have not talked about at this point absolutely require calcium to function if you don’t have the calcium then you can’t clot the blood and you’ll bleed out and that’s very bad also calcium is important

In both muscle contraction and nerve impulses generating those if you can’t generate nerve impulses or contract muscles you’re also in serious trouble so those are a few things that calcium is vital for so it makes sense to tightly regulate those levels and this is going to be a situation where it’s regulated through negative feedback so first we’re going to talk

About the situation where there’s low blood calcium we have a gland right here the major gland this one that’s kind of orange in color this is the thyroid gland of the thyroid gland we normally think of as releasing thyroid hormones however if you turn the thyroid gland around and look at its back sides of its posterior side it actually has some glands situated

On it there’s actually four of them i believe and they’re called parathyroid glands so not thyroid gland parathyroid gland because they’re sitting right on top of the thyroid and these parathyroid glands will release a substance called parathyroid hormone also called pth that’s what we’ll call it from here on out now pth is released whenever there’s a low blood

Calcium so these cells are able to sense that and when there’s low blood calcium they release pth now pth is function is to increase blood calcium levels the major way that pth is going to do this is by stimulating the activity of these cells called osteoclasts which we discussed one video ago remember osteoclast function in moving along the surface of the bone

And they degrade the bone tissue that is the matrix they break down the organic part which really isn’t important here but they break down the inorganic part that hydroxyapatite and so in doing so they release calcium into the blood and so by stimulating osteoclast activity they’re gonna generate calcium that will move into the blood and so that helps to increase

Blood calcium levels back up and that’s how pth functions it’s also worth noting that pth inhibits osteoblast activity okay its stimulates osteoclast activity obviously but it also works synergistically with another hormone called calcitriol or kalsa trial i usually pronounce a calso trial so kalsa trial is the active form of vitamin d which you need vitamin d is

Absolutely necessary for the absorption of calcium from the gut so when we consume a diet that has calcium in it calcium needs to be absorbed from the gut into the blood right however if you don’t have any calcitriol or vitamin d present you will get absolutely no calcium absorption from the gut so calcitriol the active form of vitamin d is absolutely necessary to

Absorb that calcium from the gut and the calcitriol doesn’t really play any role directly with the osteoclast but it’s worth noting that pth and cal’s a trial act synergistically both to increase blood calcium levels back to normal levels and of course pth is acting on the osteoclasts which release calcium from the bone into the blood and that brings the calcium

Levels back up that’s just negative feedback right there but that calcium level in the blood needs to be maintained okay so in other words when there is low blood calcium that stimulates bone resorption okay now what about the opposite case what if we have high blood calcium levels we also don’t want them getting too high so in contrast high calcium levels in the

Blood will stimulate bone deposition so we’re gonna deposit that calcium into the bone because it’s gonna act as a storage reservoir for the calcium now high levels of calcium inhibit release of pth from the parathyroid gland okay or the parathyroid so it’s only released when it’s low when it’s high these parathyroids don’t do anything however there’s another cell

Type within the thyroid so within the thyroid there are what we call follicular cells these follicular cells release thyroid hormone so there’s another cell type within the thyroid called para follicular cells these para follicular cells you need to differentiate from the parathyroids the parathyroids release pth the para follicular cells are actually part of the

Thyroid itself and these para follicular cells are also called c cells and they’re called c cells because they release calcitonin which starts with a c so whenever calcium levels in the blood are elevated above normal levels we need to bring it back so these para follicular cells also called c cells release calcitonin also calcitonin is a hormone just like pth and

What calcitonin does is it stimulates the osteoblast now remember when osteoblasts do they increase bone mineral density by depositing the bone matrix they function in bone deposition so in order to deposit more bone matrix they’re gonna have to take calcium which was from the blood and put it into the bone and so if you think about what that will do you’re taking

Calcium out of the blood putting into bone and so that will actually decrease blood calcium levels so in some ways the osteoblasts and osteoclasts are actually really more regulating blood calcium levels and their effect on the bone tissue is more a side effect if you want to think of it that way because maintaining this blood calcium level in a normal range is

Vital and so osteoblasts when they’re stimulated by calcitonin they deposit calcium from the blood into the bone tissue and that brings blood calcium levels back down to normal levels so the key here is when you have elevated blood calcium that stimulates bone deposition by stimulating osteoblasts through calcitonin when we had low blood calcium that stimulates

Bone resorption so release of pth which stimulates osteoclasts okay and remember pth also functions synergistically with calcitriol all right so hopefully this video gave you a really good comprehensive look at what happens in each case when we have either low blood calcium or elevated blood calcium and we see that a different hormone is released and has an affect

Positively speaking on a different cell type of the bone so hopefully this made sense to you please make sure to like this video and subscribe to my channel for future videos and notifications thank you very much

Transcribed from video
Regulation of Blood Calcium via PTH and Calcitonin By Catalyst University