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5: Bone Tissue and Skeletal System
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5.1: Introduction to Bone Tissue and the Skeletal System
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The human skeleton is the internal framework of the body. It is composed of 270 bones at birth and decreases to 206 bones by adulthood after some bones have fused together. The human skeleton serves six major functions: support, facilitation of movement, protection, production of blood cells, storage of ions, and endocrine regulation.
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5.2: Functions of the Skeletal System
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Bone, or osseous tissue, is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body. In the areas of the skeleton where bones move (for example, the ribcage and joints), cartilage, a semi-rigid form of connective tissue, provides flexibility and smooth surfaces for movement. The skeletal system is the body system composed of bones and cartilage.
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5.3: Bone Structure
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Bone tissue (osseous tissue) differs greatly from other tissues in the body. Bone is hard and many of its functions depend on that characteristic hardness. Later discussions in this chapter will show that bone is also dynamic in that its shape adjusts to accommodate stresses. This section will examine the gross anatomy of bone first and then move on to its histology.
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5.4: Bone Formation and Development
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In the early stages of embryonic development, the embryo’s skeleton consists of fibrous membranes and hyaline cartilage. By the sixth or seventh week of embryonic life, the actual process of bone development, ossification (osteogenesis), begins. There are two osteogenic pathways—intramembranous ossification and endochondral ossification—but bone is the same regardless of the pathway that produces it.
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5.5: Fractures - Bone Repair
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A fracture is a broken bone and heal whether or not a physician resets it in its anatomical position. If the bone is not reset correctly, the healing process will keep the bone in its deformed position. When a broken bone is manipulated and set into its natural position without surgery, the procedure is called a closed reduction. Open reduction requires surgery to expose the fracture and reset the bone. Some fractures can be minor and others are quite severe and result in grave complications.
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5.6: Exercise, Nutrition, Hormones, and Bone Tissue
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All of the organ systems of your body are interdependent, and the skeletal system is no exception. The food you take in via your digestive system and the hormones secreted by your endocrine system affect your bones. Even using your muscles to engage in exercise has an impact on your bones.
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5.7: Bone Classification
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The 206 bones that compose the adult skeleton are divided into five categories based on their shapes. Their shapes and their functions are related such that each categorical shape of bone has a distinct function.