Skin, muscle and bones allow movement. Skin - pliable covering. Muscles do actual moving. Bones give anchor to move against.
The skeleton functions not only as the support for the body but also in haematopoiesis, the manufacture of blood cells that takes place in bone marrow. This is why people who have cancer of the bone marrow almost always die. It is also necessary for protection of vital organs and is needed by the muscles for movement.
Watch this video to get more information about the Skeletal System:
I would also like to share how Calcium Homeostasis works.
PTH increases blood Ca2+ levels by increasing bone breakdown, Ca2+ absorption from the small intestine, and re-absorption of Ca2+ from the urine. Calcotonin decreases blood Ca2+ by decreasing bone breakdown.
Here is a video to understand more on how it works:
End of Chapter 6