0:00:00.660,0:00:05.000 So, in this video, we're going to talk a little bit about ossification, 0:00:05.010,0:00:08.800 which is the term that we use for formation of bones. 0:00:08.819,0:00:13.750 If you look at this picture over here, we've got a fetus that is forming. 0:00:13.760,0:00:19.139 And this process of ossification, or the formation of bones, actually begins 0:00:19.309,0:00:24.475 in utero and it starts at about 8 to 9 weeks of pregnancy. 0:00:24.575,0:00:26.764 So, it's actually ossification. 0:00:26.774,0:00:30.825 It's actually the formation of bone that causes us to go from 0:00:30.834,0:00:35.415 calling a developing baby an embryo to actually calling them a fetus. 0:00:35.424,0:00:37.275 So, the fetal stage begins 0:00:37.465,0:00:39.474 when we start to see bones being produced 0:00:39.485,0:00:42.115 or when we start to see ossification happening. 0:00:42.680,0:00:46.299 There are two different types of ossification and you're going to get 0:00:46.400,0:00:49.659 much more familiar with them through the activities 0:00:49.669,0:00:52.270 that you do in this particular folder. 0:00:52.340,0:00:55.119 But I want to give you just kind of a general introduction 0:00:55.130,0:00:57.950 to them now, and talk about them just a little bit. 0:00:57.959,0:01:01.549 So, the first type of ossification that I want to mention is, 0:01:01.950,0:01:02.779 Intramembranous ossification, 0:01:02.959,0:01:06.660 and the name of this particular type of ossification 0:01:06.790,0:01:11.389 gives you some information about what's actually happening here. 0:01:12.029,0:01:14.930 So “intra” is within basically, right? 0:01:15.230,0:01:16.150 And membranous 0:01:16.400,0:01:18.599 refers to a membrane. 0:01:18.739,0:01:23.519 So, this is a type of ossification that's happening within a membrane. 0:01:23.750,0:01:28.550 This is the primary way that flat bones in the body are formed. 0:01:28.559,0:01:31.349 So, there's a couple of good examples of flat bones in the 0:01:31.360,0:01:35.150 body that I want to use, in talking about this. 0:01:35.160,0:01:36.349 The collar bones. 0:01:36.360,0:01:40.730 So, the clavicles are an example of flat bones that are primarily formed 0:01:41.220,0:01:43.540 through intramembranous ossification. 0:01:44.040,0:01:46.739 In addition, the skull bones. 0:01:46.750,0:01:48.949 So, if you look at the skull on the fetus here, 0:01:49.019,0:01:51.889 they are considered to be flat bones as well. 0:01:51.900,0:01:56.330 And they form primarily again through this intramembranous ossification. 0:01:56.720,0:01:58.790 If you look at this picture over here, and you 0:01:58.800,0:02:01.940 actually look at the fetus and the skull that's forming, 0:02:01.949,0:02:06.620 you'll notice that we have these different areas that at one point 0:02:06.629,0:02:08.419 were just a fibrous membrane. 0:02:08.589,0:02:12.770 And now they're kind of starting to harden into something that's more solid, 0:02:12.779,0:02:15.070 which is bony tissue starting to form. 0:02:15.119,0:02:16.979 You'll also notice that as part of the skull, 0:02:17.205,0:02:22.375 we have big areas where it's still really just a fibrous membrane 0:02:22.514,0:02:26.705 and that intramembranous ossification has not yet occurred. 0:02:26.835,0:02:29.014 You can't see it in this particular diagram, 0:02:29.024,0:02:32.125 but there's a big area of cartilage right here 0:02:32.264,0:02:34.145 at the top of the head, where the bones 0:02:34.154,0:02:37.565 haven't fused together and where we've still just got 0:02:37.990,0:02:42.339 that membrane in which the bone will eventually ossify. 0:02:42.500,0:02:45.740 This is the soft spot that you see on infants. 0:02:45.750,0:02:49.690 It's hugely important because first of all, 0:02:49.699,0:02:54.729 it's going to allow the baby to pass through the birth canal with its head being able 0:02:54.740,0:02:56.729 to be shaped and formed and squished a 0:02:56.740,0:02:59.610 little bit because we don't have totally solid, 0:02:59.619,0:03:01.492 hard tissue making up the skull. 0:03:01.503,0:03:03.552 But we've got lots of areas of 0:03:03.563,0:03:07.522 cartilage which are softer and which are more malleable. 0:03:07.632,0:03:10.272 The other thing is during the first two years of life, 0:03:10.283,0:03:13.253 the brain is going to grow largely. 0:03:13.363,0:03:17.263 It's going to grow much larger than it was at birth, and having these 0:03:17.272,0:03:21.082 softer areas where the bones aren't fused together where we've still just got 0:03:21.093,0:03:23.113 that membrane, is going to allow 0:03:23.345,0:03:25.565 the brain to expand within the skull. 0:03:25.576,0:03:28.835 So, baby soft spots, particularly that one right here, 0:03:28.845,0:03:34.216 there's also big ones along the side that many people aren't as familiar with. 0:03:34.266,0:03:38.095 But those soft spots usually aren't completely ossified or completely 0:03:38.106,0:03:42.145 replaced with bone until about two years of age. 0:03:42.156,0:03:45.735 Which is going to allow for the brain to continue to grow. 0:03:46.235,0:03:48.505 So that's intramembranous ossification and you're 0:03:48.516,0:03:50.455 going to have a chance through the activities 0:03:50.699,0:03:53.300 that you do in this folder to learn about it more. 0:03:53.399,0:03:56.750 The other type of ossification that we see happening 0:03:56.759,0:04:00.250 in the body is what's known as endochondral ossification. 0:04:00.259,0:04:04.039 So again, you can break down the name of this type of ossification 0:04:04.289,0:04:09.000 to find out what basically is happening. And that's my whiny german shepherd. 0:04:09.740,0:04:15.899 Endochondral means that it's happening within the cartilage. So “endo” is within, 0:04:16.369,0:04:19.798 “chondral" is a term that basically means cartilage. 0:04:19.809,0:04:24.140 So, endochondral ossification is bone formation that's 0:04:24.149,0:04:27.609 happening from a hyaline cartilage model. 0:04:27.619,0:04:32.559 If you look at the picture that we have again over here, of this fetus that's forming. 0:04:32.670,0:04:35.980 You'll notice that we've got a lot of long bones and 0:04:35.989,0:04:38.660 irregular bones, and these types of 0:04:38.670,0:04:42.760 bones primarily formed through the endochondral 0:04:42.940,0:04:44.709 ossification mechanism. 0:04:44.880,0:04:48.670 And you can see, for example, if you look down here at the lower leg bones, 0:04:48.679,0:04:51.359 and then this area of the knee and the upper leg bones, 0:04:51.369,0:04:54.589 we've got bone that's forming from a hyaline cartilage model. 0:04:54.600,0:04:57.869 And then we've got areas of that hyaline cartilage model where the 0:04:57.880,0:05:02.029 bone hasn't completely formed, where we're still just looking at cartilage. 0:05:02.040,0:05:04.029 So that's the process for endochondral ossification. 0:05:04.170,0:05:09.230 It's the primary mechanism by which the other bones, 0:05:10.000,0:05:12.859 besides flat bones, are actually formed. 0:05:12.869,0:05:15.579 And in this particular type of ossification, 0:05:15.670,0:05:19.220 bones are forming from a hyaline cartilage model as 0:05:19.230,0:05:23.019 opposed to, from a membrane in the body. 0:05:23.130,0:05:27.309 One of the things that you should know about ossification though, 0:05:27.320,0:05:28.890 Is that when we say flat bones 0:05:28.899,0:05:32.019 are formed primarily from intramembranous ossification 0:05:32.640,0:05:37.070 and long bones are formed primarily from endochondral ossification. 0:05:37.130,0:05:40.559 It's not as cut and dried, it's not as black and white as that. 0:05:40.570,0:05:43.309 So, the clavicles, for example, 0:05:43.679,0:05:48.230 are representative of this. The clavicles are flat bones. 0:05:48.239,0:05:51.790 They are formed primarily through intramembranous ossification, 0:05:51.940,0:05:57.260 but there's also some endochondral ossification that happens within them as well.