Welcome to LY Med, where I go over everything you need to know for the USMLE STEP 1, with new videos every day.
Follow along with First Aid, or with my notes which can be found here: https://www.dropbox.com/sh/ces0j7obodsk5k5/AACdW5_22z2kebILxHOwYleDa?dl=0
This video kicks off our MSK block! Now MSK stands for musculoskeletal, and we'll talk about both muscles and the bone. We'll start with the bone, and in particular, our skeleton. Our bones do a ton of things. Not only are they there for support and locomotion, but they are also there for things like mineral storage, cell production and homeostasis.
Now we have a cell that builds bone and one that breaks down bone. Osteoblasts are the cells that build bone, and osteoclasts are the cells that break down bone. Now most bones start with a cartilage blueprint, and then our cells come in and turn it to woven bone, before finally turning it into lamellar bone. We call this process endochondral ossification. Some bones don't go through this process. Instead, it can make it without a cartilage blueprint.
Speaking of cartilage, there are a few types. There is hyaline cartilage, which is predominantly seen in joints. There is elastic cartilage, which is stretchy and can be seen in the ear. Finally, there is fibrocartilage, a flexible AND strong type of cartilage made up of type 1 collagen and is often seen in intervertebral discs.
Back to bone. Osteoblasts make bone by producing collagen and matrix that will eventually form bone. It likes to work in alkalinized environments, and produce ALP to help it do so.
Osteoclasts break down bone, and does the opposite of osteoblasts. It produces collagenase and acid to help dissolve bone. These cells come from monocyte precursors.
Now how the two controlled? Well the osteoblasts are the main controllers, and control osteoclasts by producing RANKL. If it wants to reduce osteoclasts, it'll make a decoy protein called OPG to reduce osteoclasts activation.
Now there are other controllers of bone formation/resorption. For example, estrogen builds bone and explains why amenorrhea causes osteoperosis! Another is PTH, which breaks down bone, by telling your osteoblasts to increase osteoclasts.
Done with bone basics, let's move on!