How does the skeletal system change as we grow?

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Claire Jeffrey

Really passionate about sharing my Human Biology knowledge!

Bone is densely packed with flexible collagen fibres, hardened by calcium and phosphorus. They are built to withstand great stress, but they don't always start off that way. Bone is a replacement tissue; that is, it uses a model tissue on which to lay down its mineral matrix. For skeletal development, the most common template is cartilage. Osteogenesis and ossification are the terms used to indicate the process of bone formation. Parts of the skeleton form during the first few weeks after conception. By the end of the eighth week after conception, the skeletal pattern is formed in cartilage and connective tissue membranes and ossification begins. Newborn babies have around 300 bones, many of which fuse together as the body matures. Babies require a constant supply of calcium in order for the skeleton to develop properly. Namely, the skull is very soft to allow for passage through the birthing canal and takes 9-18 months to harden. (I’m sure an infants skull is where sci-fi writers got inspiration for what aliens would look like) Puberty has a key role for bone development. Skeletal mass approximately doubles at the end of adolescence. The main determinants of pubertal gain of bone mass are the sex hormones as well as other growth hormones. As the cartilage growth significantly slows, the ossification rate overtakes and by this point the skeleton is laid out in bone instead of cartilage. Although there is constant remodelling and repair or bones to stress and/or other external factors. Even though bones stop growing in length in early adulthood, they can continue to increase in thickness or diameter throughout life in response to stress from increased muscle activity or to weight. So maybe you can be big boned! From about age 30, the density of bones begins to diminish in men and women. This loss of bone density accelerates in women after menopause (due to changes in oestrogen levels). As a result, bones become more fragile and are more likely to break especially in old age.