Full transcript
0:00This is the fourth video over chapter seven. We will be looking at the
0:05physiology of osseous tissue. The first thing we want to look at, is how we put
0:12minerals into our bones, and how we remove it from our bones. So
0:17mineralization, that process where we take calcium and phosphate and other
0:22ions from the blood, and put it into bone. We first need to have the osteoblasts
0:28produce collagen fibers. Then those fibers become encrusted with minerals. A
0:34few crystals need to act as a seed crystal, and that attracts more calcium
0:42and phosphate. When you make bone, you need to have both calcium and phosphate
0:49together. Sometimes you can have an abnormal calcification. We call it an
0:55ectopic ossification. You can get this calcified mass called a calculus, that
1:01forms in abnormal areas, such as your lung, or your eye, or in an artery. That's
1:07called arteriosclerosis. When we are dissolving bone and releasing the
1:14minerals into blood, this is by the osteoclasts. They're going to pump hydrogen
1:20into the extracellular fluid, chloride follows, you get hydrochloric acid, very,
1:26very low pH, and that dissolves the bone minerals. They also produce an enzyme
1:33that digests the collagen fibers, and so the amino acids that are produced go
1:39into blood. When we look at the minerals, the two primary parts is going to be
1:45calcium and phosphate. Phosphate is going to be very important because it's a
1:52component of DNA, RNA, ATP, phospholipids. Calcium is also important in a variety
2:00of different systems, for neuron communication, and muscle contraction, and
2:05blood clotting. What we find is that calcium seems to be the limiting factor.
2:13We usually don't have disorders with the phosphate, we have more disorders because
2:18of calcium. So these minerals, phosphate and calcium, are deposited in the
2:25skeleton, and then you withdraw it from the skeleton when you need it for other
2:30purposes. Calcium homeostasis really depends on a balance between what goes
2:38in the body, your intake, that's your diet, and what is lost. That's through the
2:44urinary system and fecal losses. This balance has to be maintained between
2:51your bones and blood. Calcium homeostasis is regulated by three hormones.
2:59Calcitriol is the active form of vitamin D, calcitonin and
3:06parathyroid hormone. Calcitriol, the active form of vitamin D, is a hormone. It
3:14raises your blood calcium levels. Mostly how it raises your calcium, is that it
3:22increases calcium absorption by your small intestine. It also increases
3:28calcium resorption from the skeleton, and it helps a little bit with kidney
3:35reabsorption of calcium, so you don't lose calcium in the urine. We make
3:41vitamin D through a multi-step process starting with the skin, and then liver
3:47and kidneys. So you remember, with the integumentary system, you need that UV
3:53light to start the process. Calcitriol is necessary for bone deposition. Without it
4:02your bone becomes very soft. In children this is called rickets, and in adults, we
4:11usually call it osteomalacia. In children you actually see the deformity. In adults,
4:18the main symptom is pain. Let's look at the next hormone.
4:24This is calcitonin. This is produced by your thyroid gland. We
4:29release calcitonin, when you have very high blood calcium. This will lower your
4:36blood calcium in two ways. First of all, it's going to slow down the osteoclasts.
4:42So remember, the osteoclasts are breaking down bones, and then it stimulates the
4:49osteoblasts. Remember they're the ones making bone. So you're going to be making
4:54bone faster than you break down bone. Calcitonin appears to be more important
5:01in children, because they're growing their skeleton. It has a very weak effect
5:06in adults, except maybe in pregnant women and lactating women. Parathyroid hormone
5:15is produced by the parathyroid glands These are glands that are embedded in
5:20the posterior part of your thyroid gland. We release parathyroid hormone when you
5:28have low blood calcium. Parathyroid hormone or PTH increases blood calcium
5:35four ways. One, you're going to stimulate the osteoclast and start breaking down
5:41bone faster. You're going to promote calcium reabsorption by the kidneys, so
5:49you do not lose so much calcium through urine. You're going to promote vitamin D
5:56synthesis, and then you're going to slow down the osteoblasts, and so it slows
6:02down bone formation. Alright, so this is a figure that can be a little bit confusing. You
6:11notice that the amount of calcium in your blood is in a range. So that is the
6:17most important thing, is your blood calcium. The arrows going to the blood,
6:23these are hormones that are going to increase your blood calcium, so vitamin D.
6:30You're going to absorb more calcium from the digestive tract, put it into the
6:35blood, bring up your blood calcium. We have vitamin D
6:39and parathyroid hormone. This is going to stimulate those osteoclasts, and you
6:45start breaking down bone, put the calcium into your blood. You also use parathyroid
6:53hormone to reabsorb calcium from the kidneys, and prevent it from being lost
6:59in urine. Now what is leaving your blood? You have calcitonin, that deposits
7:08calcium into your skeletal system. So it says it's a very weak effect on this.
7:13This is more important in children, and then you always lose some calcium in
7:20your kidneys. Alright, so let's go ahead and present this in a little bit more
7:27simple fashion. We look at your blood. You have a calcium range; it needs to stay in
7:34that range. If it gets too high, that is going to lead to death. If it gets too
7:39low, that's going to lead to death. What we find with your blood calcium, is that
7:46it is like a slow draining sink. That blood calcium is always going to go down.
7:54Why is it always going to go down? Because you're going to be using it. You
7:59pull out calcium for the muscles. You pull out calcium for the nerves, for all
8:05these different things. You will also lose calcium through your urine, and so
8:12that's why your blood calcium is always going to go down. Now how do I bring it
8:18back up into the range? Well the main thing is with your food. You use one of
8:25your hormones, vitamin D calcitriol, you absorb the calcium out of your food, and
8:31that brings up your blood calcium. Now let's put in our skeletal system. What is
8:39that skeletal system? Well actually it's a bank. This is the bank for your calcium
8:45and phosphate, and we are most interested in the calcium part.
8:51When you are a child, you need this hormone, calcitonin, to take the calcium
8:58from your blood, and put it into your skeleton. This is very important, because
9:04your skeleton is growing. So you always need to add calcium to that skeleton. Now
9:11we say it's weak in an adult, and it's because in an adult, we are not growing
9:17our skeleton. We are remodeling it. That means how fast you break it down, and how
9:24fast you build it, should be the same. Al- right, so here this blood calcium is
9:31always going to go down. So you can't eat 24 hours a day. Where are you going to
9:38get the calcium when it goes down too low? Well you're going to get it from the
9:43bank, and how are you gonna do it, is with parathyroid hormone. This is like your
9:49ATM card, so I'm going to withdraw from that skeleton, your bank, and add calcium
9:56to my blood. Now what else does PTH do? It helps prevent too much calcium from
10:04being lost in the urine. So you pull it out of your kidneys, put it back into the
10:09blood. When you've got enough blood calcium, then you put away your ATM card.
10:17So the amount of PTH then goes down. Only when the blood calcium goes down, do you
10:25pull out that ATM card and withdraw some more calcium. Let's look at our negative
10:32feedback loops. If you have an excess of calcium, then you're going to produce
10:39calcitonin. That is going to slow down the osteoclast, so you get less bone
10:45that's broken down. And it's going to speed up the osteoblasts, so you make
10:51more bone, and since you are making more bone, then your blood calcium goes back
10:57down to normal. If your blood calcium is very low, then you're going to release
11:04parathyroid hormone, and so what does that
11:07parathyroid hormone do? You are going to speed up the osteoclasts, so that they
11:13are breaking down more bone. That calcium goes back into the blood.
11:18You're gonna slow down the osteoblasts. You are actually going to get rid of
11:24some phosphate from your blood, and so you excrete it in the urinary system. If
11:30you don't have phosphate, then you can't make bone, and then you make sure that
11:37the calcium is not lost in the urinary system. All of this will bring your
11:43calcium back up to normal. Now having too much calcium and not enough calcium in
11:52your blood is dangerous. So hypocalcemia is low blood calcium; it will actually
12:00over excite your nervous system, and send too many messages to your muscles. Your
12:07muscles start to spasm and contract, and you have no control over it. One of the
12:15muscles that are going to be important is there at your larynx, and if that
12:21contracts and doesn't relax, that will cause suffocation, and so this
12:27will lead to death very quickly. Some cases of hypocalcemia is because you
12:33have a deficiency of vitamin D, or you do not have enough parathyroid hormone.
12:39Women who are pregnant or lactating have a higher risk of hypocalcemia.
12:47Hypercalcemia is too much calcium levels, and this makes the nerves and muscles
12:54less excitable, and they're not able to contract. This can cause muscle weakness,
13:01cardiac arrests, some emotional disturbances. This is very rare, this
13:08hypercalcemia, because remember, that the amount of calcium in your blood is like
13:15a slow drain on a sink. It is always going down. This
13:21is why hypocalcemia is more likely to occur than hypercalcemia. So this is a
13:33clip of a patient who has hypocalcemia. They're going to inflate his
13:40blood-pressure cuff, and what's going to happen is his fingers are going to
13:46contract. He has no control over it, that is a sign of very low blood calcium. This
13:55is called trousseau's sign. Raise your hand for us. Good. Squeeze like that. Good. Then back out. You can relax your hand and keep it like this, please. Just let us know what you are feeling as we are doing this. It's trembling right now, going to sleep. Okay. Now it's starting to curl. What do you mean trembling? It's going like this; it's shaking. Can you control your hand? No. Okay. It's going
14:33like this by itself. Try to straighten your fingers out. I can't. You can't do it. I can't. What do you
14:39feel right now? I want to go like this, and flatten them out. You are trying to. Yeah
14:44but I can't. This goes way in here like this and will not move. Now look, it's crunching even more. And you're not doing it. I'm not
14:53doing that. Okay. Matter of fact, I want to pull it
14:57back out. See the other one was doing it too. Right. This is what happen earlier to you. Mm-hmm, that's what
15:03happened over here. Okay. It went just like that. I'm gonna release the pressure now. See it's pulling it more down.
15:14Let us know how you feel. There, see. Now what's it feel like? Fine, well it is not fine, but it's sleep.
15:19I see, now move your fingers, for us, okay. Great. Wonderful.
15:24Thank you Sir. In infancy and childhood the epiphyseal plate activity is stimulated
15:35by a lot of different hormones. The main one that we want you to know is human
15:40growth hormone. In puberty, you start producing testosterone and estrogen. That
15:47promotes that growth spurt; it also will help differentiate the male and female
15:54skeleton. Bone growth, ends anywhere between 18 to 20 years is typical. Now
16:02girls grow faster than boys, and reach full height earlier, and the reason is
16:08estrogen. It has a stronger effect than testosterone on bone growth. Males will
16:14grow for a longer time, and so they're taller. However, if they use anabolic
16:20steroids, this can cause growth to stop, and so
16:25those epiphyseal plate closes prematurely, and that results in someone
16:30who's abnormally short, okay. So this is the end of video four. The last video is
16:38going to look at bone disorders.