In this video, we're going to talk about the first type of cartilaginous joint in our lesson, which is the synchondrosis. And the plural form is synchondroses. Synchondroses are cartilaginous joints where bones are bound specifically by hyaline cartilage. It's helpful to recall that the root chondro, which is found in the word synchondroses, is a root that means cartilage. Recall from our previous lesson videos on cartilages that hyaline cartilage is a tough yet flexible specialized connective tissue that can resist tension forces.
The hyaline cartilage in these synchondroses makes these joints structurally stable. They provide structural stability. However, recall that structural stability of a joint comes at the cost of the mobility of the joint. Although these synchondroses provide structural stability, they essentially allow no movement. Therefore, they are always classified functionally as synarthroses.
Which is why we have the symbol for synarthrosis here in our lesson. And again, notice that the symbol for synarthrosis does not have any movement arrows going around it. Because it doesn't have any movement arrows going around it, hopefully that can be a helpful reminder that these synarthroses are still or stationary joints that essentially allow for no movement and are generally considered immovable joints. Now, similar to sutures, eventually, some synchondroses bones may actually fuse together to become a synostosis or a bony joint. Recall that the root ost is a root that means bone, and so hopefully that can remind you that a synostosis is when two or more bones fuse together into a single bone.
The hyaline cartilage in these synchondroses can eventually ossify. And, of course, that means that it can be replaced by new bone tissue. Not all synchondroses are going to ossify to become a synostosis. Only some of them will, and usually the ones that are involved with growth and development are going to turn into synostoses, such as the epiphyseal plates, which we'll get to see down below in our image.
Notice here, in the middle of the image we have this human skeleton and we're focusing on very specific regions. On the left hand side, we're focusing on the femur. You can see here is the femur. Notice that we're zooming into the top portion here of the femur. What you'll notice is that these blue lines that you can see here and here, where we're indicating with these arrows, these are the epiphyseal plates.
Also, sometimes referred to as growth plates. These are synchondroses; there is hyaline cartilage that is connecting bones. It is connecting the epiphysis of the bone to the diaphysis of the bone. These epiphyseal plates can be found in long bones, such as the femur, the humerus, and the tibia, for example.
These epiphyseal plates, again, in children and adolescents, they will be present. But, when they reach adulthood, these epiphyseal plates are going to ossify, and the bones will fuse together to create synostosis. Now, notice over here on the right side, we're focusing on another example of synchondrosis, which is between the first rib and the sternum, specifically the manubrium of the sternum or the superficial portion of the sternum. Notice, here we have the first rib and the first rib is being connected to the manubrium of the sternum or the superficial portion of the sternum by the hyaline cartilage that you can see here. This is a synchondrosis.
It is only the first rib, that is the junction that connects the first rib to the sternum that is considered a synchondrosis. Many of the other ribs that lie beneath are going to have junctions that are considered synovial joints. We'll get to talk more about those later in our course. But for now, this concludes our brief lesson on synchondroses, and we'll be able to get some practice applying these concepts and learn about the other type of cartilaginous joint as we move forward in our course. So, I'll see you all in our next video.
