Chapter 4

Chapter 4 - Chapter 4 Development of Aging of Body Systems...

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Chapter 4: Development of Aging of Body Systems Postnatal growth, development, and aging are products of genetic and extrinsic influences. o Development of the Skeletal System Early Development of the Skeletal System Skeleton is a living tissue. In embryonic life, the skeleton is a “cartilage model” of the bones. At fetal age of 2 months, primary ossification centers appear in midportions of the long bones. POC (400) are areas in the midportion of the shafts of long bones where bone cells are formed so that the cartilage model bones of the fetal skeleton begin ossifying, from the center outward, to form bone shafts. Postnatally, secondary ossification centers at the end of shafts (epiphyseal plate=growth plate=pressure piphysis) are the areas where new bone cells are formed and deposited so that the bones grow in length. It is a layer of cartilage cells that can be detected by a thin line in X-rays. Because linear growth is almost completely the result of skeletal growth, measures of stature reflect the linear growth of bone. The epiphysis between muscle tendons is called traction epiphyses. The epiphysis growth stops at 15.5 in girls but 18.1 in boys (average). Appositional bone growth is responsible for the increase in circumference of the bones, by adding new layers under old ones. Aging of the Skeletal System 1% of the bone mass in adults are resorbed every year (starting from mid 20s). Adults have seven times more inorganic components in bone, making it more brittle than those of children’s. Adult’s may suffer from osteoporosis, a major bone mineral disorder in which the victim experiences loss of bone mass and thus bone strength (bones become abnormally porous through the enlargement of the canals or the formation of spaces in the bone. Hormone level, diet, and exercise are extrinsic factors that influence bone loss. Development of the Muscular System Early Development of the Muscular System At birth, muscle weighs about 25% of body mass. The sigmoid pattern of growth in weight reflects the growth of muscle tissue. Muscle length grows by the addition of sarcomeres (contractile units) at the muscle, tendon junction as well as the lengthening of
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sarcomeres. In male adults, muscle mass is about 54% of the total body weight. In female adults, 45%. Three main muscle fiber types: type I (slow-twitch) fibers for endurance
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This note was uploaded on 08/02/2008 for the course EDKP 261 taught by Professor Staples during the Fall '07 term at McGill.

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Chapter 4 - Chapter 4 Development of Aging of Body Systems...

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