Skeletal System PDF

S KE LE TAL S YS T E M DAVAO MEDICAL SCHOOL FOUNDATION, INC. College of Nursing M. Platero, RN, MD, FPCP » Individual bones are the organs of the skeletal system. » A bone contains active tissues. » Bones support and protect soft tissues, provide attachment for musc...

S KE LE TAL S YS T E M DAVAO MEDICAL SCHOOL FOUNDATION, INC. College of Nursing M. Platero, RN, MD, FPCP » Individual bones are the organs of the skeletal system. » A bone contains active tissues. » Bones support and protect soft tissues, provide attachment for muscles, house blood producing cells, and store inorganic salts. Bone classification Bones are grouped according to their shapes—long, short, flat, irregular, or round (sesamoid) Parts of the skeletal system begin to form during the first few weeks of prenatal development, and bony structures continue to grow and develop into adulthood. Bones form by replacing existing connective tissue in one of two ways. Some bones originate within sheet-like layers of connective tissues; they are called intramembranous bones. Others begin as masses of cartilage later replaced by bone tissue; they are called endochondral bones. Homeostasis of Bone Tissue After the intramembranous and endochondral bones form, the actions of osteoclasts and osteoblasts continually remodel them. Bone remodeling occurs throughout life as osteoclasts resorb bone tissue, and osteoblasts replace the bone. These opposing processes of resorption and deposition are highly regulated so that the total mass of bone tissue in an adult skeleton normally remains nearly constant. Factors Affecting Bone Development, Growth, and Repair Vitamin D is necessary for proper absorption of calcium in the small intestine. In the absence of this vitamin, calcium is poorly absorbed, and the inorganic salt portion of bone matrix lacks calcium, softening and thereby deforming bones. In children, this condition is called rickets, and in adults, it is called osteomalacia. Vitamin A is necessary for osteoblast and osteoclast activity during normal development. This is why deficiency of vitamin A may retard bone development. Vitamin C is required for collagen synthesis, so its lack may also inhibit bone development. In this case, osteoblasts cannot produce enough collagen in the extracellular matrix of the bone tissue. As a result, bones are abnormally slender and fragile. Factors Affecting Bone Development, Growth, and Repair The pituitary gland secretes growth hormone, which stimulates division of cartilage cells in the epiphyseal plates. In the absence of this hormone, the long bones of the limbs fail to develop normally, and the child has pituitary dwarfism. He or she is very short but has normal body proportions. If excess growth hormone is released before the epiphyseal plates ossify, height may exceed 8 feet— a condition called pituitary gigantism. In an adult, secretion of excess growth hormone causes acromegaly, in which the hands, feet, and jaw enlarge When the blood is low in calcium, parathyroid hormone stimulates osteoclasts to break down bone tissue, releasing calcium salts from the extracellular matrix into the blood. On the other hand, very high blood calcium inhibits osteoclast activity, and calcitonin from the thyroid gland stimulates osteoblasts to form bone tissue, storing excess calcium in the extracellular matrix Joints or articulations are functional junctions between bones they bind parts of the skeletal system, make possible bone growth, permit parts of the skeleton to change shape during childbirth, and enable the body to move in response to skeletal muscle contractions.