In this video, we are going to discuss what happens when blood calcium levels get too high, how your body reacts when blood calcium levels are high, what structures are involved to maintain homeostasis of blood calcium, and what type of feedback does this process involve. So it's really important to first know what is your normal blood calcium serous levels, and your normal blood calcium serous levels. are going to be 8.6 to 10.3 deciliters per milligrams.
Now this is what is considered your normal physiological limits, but remember that we can fluctuate and everyone is going to be unique, but anytime we start to meet or start to reach the edges of the physiological limits, then your body will definitely make some type of change. to help you maintain homeostasis. Now the goal is that you kind of stay wherever your physiological limits are. So anytime that you start to fluctuate, whether it's going high or whether it's going low, your body is constantly making changes so you can be maintained at whatever your normal is.
So this process doesn't just happen when we get too high or too low, it's constant. But sometimes it does fall really low or rise really high relatively quickly and your body does make changes. So in this particular video, we will be discussing what happens if your blood calcium levels rise too high.
Now before we start that, we just need to go over your basic homeostasis again. So if you remember, when we talk about homeostasis, homeostasis is controlled by a feedback cycle, and the feedback cycle is going to have five major components. So the first component that it's going to have are the sensory receptors. The sensory receptors are constantly monitoring the controlled condition. The controlled condition is anything that your body tries to maintain.
And in this case, our controlled condition is calcium blood serum levels. So the sensory receptors are going to monitor that. And any type of change that may occur to those levels, it will detect that.
Now, usually some stimulus occurs that causes a change. The sensory receptors detect that change and they're going to send input. Input can be chemical or electrical.
If input is chemical, it is endocrine. If it's electrical, it's the nervous system controlling it. Input is going to go to the control center. The control center is going to evaluate this information and from that information it sends output. Output again is a signal.
It's going to be either a chemical controlled by the endocrine or an electrical controlled by the nervous system. And that output is going to go to an effector. Effectors are muscles and glands, oftentimes cells, that will bring about a change. This change can go back to normal or the change can cause it to go further away from normal. Regardless, though, these are the steps and the components that are present in all feedback cycles to help us maintain homeostasis.
So if our blood calcium gets too high, that... is going to be some type of stimulus that disrupts our levels. Our levels are basically between 8 and 10. So anytime it gets close to that 10, that's disrupting the blood calcium levels.
And when the blood calcium levels are disrupted, we are going to have a sensory receptor detect that. Now in this case, the sensory receptors are on the thyroid gland. Your thyroid gland, this is a posterior picture of it.
It is the pink area right here. It is not the green dots. Those are the parathyroid glands.
Your thyroid gland basically sits on your neck on top of your trachea. There are very specific cells in the thyroid gland. This is a front view of it.
These cells are called the hairl follicular cells. These cells are also known as C cells. Makes it much easier to remember. So the paraphilicular cells are going to detect this.
change in blood calcium levels. When they detect the change in blood calcium levels, the C cells are going to let out a signal. This signal is input.
Now the input the C cells let out are actually going to be what I call a boomerang effect. They release this chemical signal. That chemical signal goes right back to the C cells and it actually activates a gene inside of that cell.
So I like to call this the boomerang effect. This signal is considered an autocrine signal. So basically the signal acts on itself.
Again, unofficial name is boomerang effect. So if you know what a boomerang is, boomerangs you throw out, they come back. So let's pretend that this is your C cell. Your C cell is going to release a signal. When it releases this signal, The signal goes outside of the cell and then on the outside of the cell we got a receptor.
That signal that is released, that chemical, is going to go and attach to the receptor. When it attaches to the receptor it actually activates a gene inside of the c cell. So the signal is released by the c cell and it turns the c cell on. It activates it. So this is autocrine signaling, basically speaking to itself, auto.
And once this C cell is activated, that's basically your control center. So both your receptors and your control centers are the C cells. The C cells get activated. And when they're activated, they're going to release output.
Output is going to be calcitonin. Calcitonin is a chemical. So this is an endocrine output. Calcitonin is also known as CT. It's just the shortened version of it.
Calcitonin is released into the blood and then it's going to travel to the effectors. In this case, the effectors, there are three of them. Two major ones and one that's kind of indirectly affected. The two major ones are osteoclasts and the kidneys. Now, our problem is our blood calcium levels are too high.
So we don't want to... break down more bone and put more calcium into your blood. So that means we don't want osteoclast working. So what happens is we basically tell osteoclast to slow down.
CT is going to attach to osteoclast. So osteoclasts actually have receptors. CT will attach to those receptors and it will inhibit our slow down osteoclast.
At the same time, CT... We'll signal the kidney. CT will tell the kidney to get rid of urine, to get rid of calcium in the urine.
So we are stopping your bone from putting more calcium into the bloodstream. And we are asking the kidneys to release more calcium in urine. So we're getting rid of calcium because our calcium levels are too high. So the kidney gets rid of calcium. The osteoclast stops.
breaking down bone so we're not producing more calcium. So these are the two main ones, but there is an indirect effect. The indirect effect is that osteoclasts will also signal osteoblasts.
Osteoblasts build bone. And what do we know we need to build bone? We need calcium.
So indirectly, we tell osteoblasts to increase activity. So now we are getting rid of calcium in our urine. We have osteoclasts not breaking down new bones, so we're not producing new calcium into the blood. And we have osteoblasts building bone, so we're getting rid of extra calcium in our blood and putting it into the bone. When we do all of this, our calcium levels will decrease.
They'll drop back down to normal, and when they drop back down to normal, we're going to stop signaling the parafollicular cells to release calcitonin. So When calcium levels get too high, our goal is to lower that calcium level in our blood, and we do that by releasing calcitonin. It tells our kidneys, let's pee out some more calcium. It tells our osteoclast, don't break down any more bone.
And indirectly, we tell our osteoblasts, hey, build more bone, build more bone. So when we look at it, we have our stimulus, which is whatever disruption is in our blood calcium levels. our blood calcium levels are being disrupted your c cells aka parafollicular cells they notice that they're going to send input input is going to be an auto cringe signal because it basically goes back to itself so the c cells send a signal to themselves and they activate the gene inside and that gene is going to help us increase ct ct is our output it's again a chemical output that chemical output is based on the endocrine system. So CT travels through the blood.
Osteoclasts have a receptor for CT, so it binds to osteoclasts and tells it don't break down bone. It binds to the kidneys, the kidneys have a receptor for CT. It tells the kidneys, hey pee out calcium, and then indirectly the osteoclasts tell osteoblasts Hey buddy.
We need to build more bone. By building bone, we're taking all this extra calcium from blood and we're storing it in bone. All three of these actions together help us decrease blood. Then we're going back to normal. If we're back to normal, this is a negative feedback cycle.
This is the same concept, it just shows it in a more of a linear line than in a circle. And here we're going to go over a few questions. So calcitonin decreases increases the activity of.
Which cell do we not want to put more calcium into our bloodstream? Which cell do we not want breaking down bone? You said class, you are correct. Calcitonin indirectly increases the activity of. Well, if we're increasing the activity, that means this cell is going to work more.
And if it's working more, that means it's going to be building more bone to get rid of calcium in the blood and put that calcium into your bone. So the one that builds calcium. into your bone is osteoblast. Calcitonin is going to signal the kidney and when it signals the kidney, is it going to tell the kidney to hold on to that calcium or get rid of that calcium? If you said get rid of, you are correct.
So just remember when we talk about calcium homeostasis, the goal is to understand which cells are helping us either increase calcium levels or decrease calcium levels. In this particular scenario, we talked about calcium levels that were too high. When calcium levels are too high, calcitonin tones down the calcium levels. So when calcium levels are too high in the blood, calcitonin, emphasize that again, tones down your calcium levels. Calcitonin tones down calcium levels.
It does that by acting on osteoclasts in your kidney directly. And it does that by indirectly acting on osteoblasts. We do not want any more calcium in our blood.
So it tells osteoclasts don't work. And we need to get calcium out of our blood into our bones. So it tells osteoblasts, please work, increase that activity. And we don't want to hold on to any more calcium.
So calcitonin tells your kidneys to pee it out. All of this together helps us get our calcium levels back down to normal. And that's...
maintaining our homeostasis.