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Skeletal endocrine control
Created by Tracy Kim Kovach.
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The teacher mentions that an increase in calcium is always accompanied by an increase in phosphate. What does the phosphate in the bones and in the blood actually do?(10 votes)
As mentioned near the end of the video, calcium is critical for muscle contraction and brain function. In fact there is an entire class of drugs called "calcium channel blockers" that are used to treat heart problems. Phosphorus, on the other hand, is a critical part of the energy system of the body as it is used in to make adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP). So, isn't it cool the way our bodies can store these 2 critical elements in our skeletons to be taken out of storage when needed? Hopefully, this makes you want to drink your MILK, which is not only very high in both calcium and phosphorus, but also a great source of protein.(19 votes)
Since exercise strengthens bones, or increases bone density, does that mean the osteoblasts are taking Ca and PO4 out of the blood? Is this process enhanced immediately after exercise? And what signals bone to increase its density after exercise (how does it "know" you exercised)? Mechanical force conveys a signal, or signaling molecules secreted from muscle?(6 votes)- The way it works (or at least the way that we think it works) is actually really simple and elegant. When you put a force on a bone during exercise, that force will be transmitted to the osteocytes (the cells that make up the bone). These osteocytes are able to make a signal molecule that lets the osteoblasts know that they are feeling forces from exercise. Osteoblasts will first signal for the osteoclasts to come in and dig "Tunnels" in the bone wherever the force was applied (wherever the osteocyte signal molecules are) , and then the osteoblasts follow behind the tunneling osteoclasts and fill in the tunnels to make the bone even stronger in those areas than it was initially. Over time this results in the gradual strengthening of bone ONLY in the areas that are frequently under stress, because those are the areas that need to be the strongest.
When the osteoblasts are mineralizing bone, it does mean that Ca+ and PO4 will be taken out of the blood, but this is actually a really good thing. You might have low [Ca+] or [PO4-] in your blood for a short period of time, but pretty quickly vitamin D will go up, and that will work to increase the Ca+ and PO4- absorption from your digestive tract. This brings your Ca+ levels back up to normal, and means that you were able to build a little bone in the process.(16 votes)
I don't think this is correct. PTH causes elevation of Ca in the blood but PO4 goes down due to renal absorption.
Anyone?(7 votes)
From what I've learnt, PTH decreases phosphate reabsorption in the kidneys so more is excreted
Wikipedia explains in more depth that there is an overall decrease in serum phosphate like you mentioned: https://en.wikipedia.org/wiki/Parathyroid_hormone#Regulation_of_serum_phosphate(1 vote)
In the video it was mentioned that calcitriol increases osteoclast activity and decreases osteoblast. Does that mean taking in Vitamin D supplements actually degrade bone?(2 votes)
No, vitamin D helps your body absorb calcium into the blood. Without this, calcium has little capacity to enter the bloodstream to be delivered to the bones. Vitamin D does not affect osteoblasts' activity to deposit calcium, it stimulates osteoblasts to secrete more proteins such as osteopontin to prepare the bone matrix for mineralization. I do find the table presented in the video oversimplified and confusing.(8 votes)
- why do we need PTH and calcitriol if they do the same job?(4 votes)
- Calcitriol increases Ca absorption in the intestinal tract.(3 votes)
So, if I eat lots of spinach/consume lots of dairy products (for calcium), drink lots of Coke (for phosphate, via phosphoric acid), and take vitamin D supplements for bone growth, can I expect my bones to get thicker?(1 vote)
Consuming more nutrients may not lead to larger bone mass as it is difficult to predict where they will be used. In any case, I couldn't recommend anyone drink lots of Coke due to the extremely high sugar content.
However, exercise has been proven to increase bone mass and bone strength.(10 votes)
If you drink more milk do you have a less chance of getting arthritis in the future?(2 votes)
Probably not, since arthritis is caused by a break down in cartilage, and cartilage doesn't use calcium.(4 votes)
so what is the difference between PTH and calcitronin?(1 vote)
Calcitonin is released by the thyroid to decrease blood Ca2+ by inhibiting osteoclasts; in effect, it allows more growth of your bones. I remember it by saying "calcitonin tones your bones".
PTH is released by the parathyroid to increase blood Ca2+ by stimulating proliferation of osteoclasts.
They're hormones so they act to bring systems back to homeostasis. So if the body is running low on Ca2+ in the blood, PTH will be released to increase blood Ca2+. But if there's plenty of Ca2+ in the blood, calcitonin will be released to take out Ca2+ and use for bone formation.(4 votes)
she said that calcium absorption by the intestine/kidneys will cause the calcitonin activity to decrease. But, if the calcium levels in the blood increases,doesnt that mean the calcium absorption in the intestine would decrease? since there a lot of calcium in the blood.(2 votes)
what does the calcium in the bones do?(1 vote)- Calcium provides hardness so bones are strong and can support our weight. Hydroxyapatite is the building block of bone.(2 votes)
Video transcript
- [Voiceover] Now, one
of the main functions that bone performs is as a storage source of calcium. So now you know why your mom told you that you needed plenty
of calcium, probably in the form of a tall glass of cold milk, so that you could form strong bones. So calcium homeostasis,
or, the flow of calcium between the blood stream
and bone is actually under endocrine or hormonal control. And these hormones,
these endocrine hormones actually alter the ratio
of osteoclast activity to osteoblast activity. So as osteoclast activity
increases relatively to osteoblast activity,
there is an increase in the liberation of calcium and phosphate from bone into the blood stream. And remember that osteoclasts
cause bones to crash. So they take the calcium
and phosphate from bone and put it into the blood stream. The opposite is true
if this ratio reverses. As the activity of osteoblasts increase, you get calcium and phosphate going from the blood stream back into bone. So that's the gist for
calcium homeostasis. Now what are the main
players, the hormones that are responsible for maintaining
this calcium homeostasis, this balance between calcium and phosphate in the blood stream and calcium
and phosphate in the bone? Well, the main players
are parathyroid hormone, calcitonin, and a third
hormone called calcitriol, which is really just the
active form of vitamin D. These hormones basically help to regulate the amount of calcium
that is either absorbed from the gut or reabsorbed
from the kidneys. And they also affect the level
of activity, or this ratio, of osteoclast to osteoblast activity. Parathyroid hormone, or
P-T-H, and calcitriol have the same overall effect
of increasing calcium and phosphate in the blood,
with calcitonin having the opposite effect. It decreases the amount
of calcium and phosphate in the blood. And the way I remember this is that calcitonin actually tones
down the calcium in blood. And so, as you can see, there couple of general themes here. The first being that each
time calcium increases in the blood, you have a concurrent increase of phosphate. They kind of go together. They're buddies. And the same thing for if
calcium decreases in the blood, phosphate will decrease. The other thing to kind
of keep in mind is that, as calcium or phosphate
increases in the blood, there is a concurrent decrease of these two ions in bone. It has to be coming from
the bone if it's going to be increasing in the blood. And the opposite is true
for whenever calcium and phosphate is decreasing
from the bloodstream. It's decreasing because
it's being placed back into bone, deposited in the form of bone. So one thing that I think
would be particularly helpful is if we draw out a table and go through how each of these hormones affects the cellular activity of
osteoblasts and osteoclasts, and also calcium absorption from either the intestines or the kidneys. So here, going 'cross the table, we'll put parathyroid hormone,
calcitonin, and calcitriol. And then we'll put each of the things that is affected by the various levels of these different endocrine players. Osteoblast activity, we'll
put osteoclast activity, and then intestinal or
renal absorption of calcium. So first, let's look
at osteoblast activity. Recall that osteoblasts build up bone. As their activity
increases, you have calcium and phosphate taken from the blood stream and deposited into bone. Now keeping that in
mind, and also realizing that parathyroid hormone
helps to increase calcium and phosphate in the
blood, in other words, it breaks down bone to put
calcium phosphate in the blood, we would expect osteoblast
activity to decrease as parathyroid hormone increases. So that's the effect parathyroid hormone has on osteoblast activity. It decreases it. And calcitriol, remember,
has the same overall effect that parathyroid hormone has. It increases calcium and
phosphate in the blood by taking it from bone. So as calcitriol
increases, you would expect osteoblast activity, the
activity of building bone, to decrease because you're
taking calcium and phosphate from the bone and putting it in the blood. Calcitonin, on the other hand,
remember, tones down calcium and phosphate in the blood. It takes these ions and
puts it back into bone. And so, as calcitonin increases, we would expect osteoblast
activity to increase. Because more bone is
being formed from calcium and phosphate being taken from the blood. And you'll see this theme
of parathyroid hormone and calcitriol having the same effect on either osteoblast
activity, osteoclast activity, or the absorption of
calcium because they have the same effect of increasing
calcium and phosphate in the blood. So next, let's go to osteoclast activity. This is basically going to be the opposite of whatever osteoblast activity is. Because remember
osteoclasts crash down bone. They take the calcium and
phosphate and put it back into the blood stream. And remember that parathyroid
hormone stimulates this process. So the effect of parathyroid hormone on osteoclast activity is to increase it. And likewise, calcitriol is going to increase osteoclast activity. And then calcitonin,
because it decreases calcium and phosphate being put
into the blood stream, is going to decrease
this osteoclast activity. So now we're on to intestinal and renal, or kidney, calcium absorption. Knowing that parathyroid hormone leads to an increase in calcium and
phosphate in the blood, we would expect parathyroid
hormone to lead to an increase in the
ability of the intestines and kidneys to absorb calcium. And we know that calcitriol
has this same effect. Calcitonin, on the other
hand, we remember tones down calcium in the blood, so
we would expect calcitonin to decrease the rate of calcium absorption via the intestines and in the kidneys. So why does the concentration
of free calcium ions in the blood matter so much? Why does our body have
this elaborate system of calcium homeostasis with
these various hormones, and altering the concentrations
of calcium and phosphate between the blood stream and bone? Well, the concentration of calcium ions in the blood actually has very important physiological effects. So, for example, too much
calcium actually leads to hypoexcitable cell membranes. And this results in lethargy,
fatigue, and memory loss. Whereas, too little calcium
in the blood actually leads to muscle cramps and convulsions. So, as you can see, the
endocrine system plays a pretty critical role
in calcium homeostasis through its effect on bone remodeling and its effect on calcium absorption.