Anatomy & Physiology

Anatomy & Physiology Study Guide • Spongy bone is located where stresses are few or come from many directions, such as at the epiphyses of long bones. Ossification and appositional growth are mechanisms of bone formation and enlargement: • Ossification is the process of converting other tissues to bone. Calcification is the process of depositing calcium salts within a tissue. • Endochondral ossification begins with a cartilage model that is gradually replaced by bone at the metaphysis. In this way, bone length increases. • The timing of closure of the epiphyseal cartilage differs among bones and individuals. • Bone diameter increases through appositional growth. • Intramembranous ossification begins when osteoblasts differentiate within connective tissue. The process produces dermal bones. Such ossification begins at an ossification center. • Three major sets of blood vessels provide an extensive supply of blood to bone. Bone growth and development depend on a balance between bone formation and bone resorption: • The organic and mineral components of bone are continuously recycled and renewed through remodeling. Exercise, hormones, and nutrition affect bone development and the skeletal system: • The shapes and thicknesses of bones reflect the stresses applied to them. • Normal osteogenesis requires a reliable source of minerals, vitamins, and hormones. • Growth hormone and thyroxine stimulate bone growth. Calcitonin and parathyroid hormone control blood calcium levels. Calcium plays a critical role in bone physiology: • Calcium is the most abundant mineral in the human body; roughly 99 percent of it is housed in the skeleton. • Interactions among the bones, digestive tract, and kidneys affect the calcium ion concentration. • Two hormones, calcitonin and parathyroid hormone (PTH), regulate calcium ion homeostasis. Calcitonin leads to a decline in the calcium concentration in body fluids, whereas parathyroid hormone increases the calcium concentration in body fluids. A fracture is a crack or break in a bone: • A break or crack in a bone is a fracture. The repair of a fracture involves the formation of a fracture hematoma, an external callus, and an internal callus. Osteopenia has a widespread effect on aging skeletal tissue: • The effects of aging on the skeleton include osteopenia and osteoporosis.

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