Bones are alive Living bones Form Grow Repair
Bones are alive • Living bones: • Form • Grow • Repair • Remodel • Move at joints (with help from muscles)
Skeletal System – Normal Function Skeletal System Normal Function Movement Protection Support Mineral Storage Blood Cell Production
Bone Types
Long Bone – Macroscopic Anatomy Epiphysis (end) • covered with hyaline cartilage • compact bone forms exterior • spongy bone forms interior • contains epiphyseal line/plate Diaphysis (middle) • compact bone forms exterior • center composed of the medullary cavity containing yellow or red marrow. Marrow helps produce red blood cells. Fig 7. 1
Long Bone – Macroscopic Anatomy Fig 7. 2
Microscopic Anatomy • Osteon = circular structure organized around blood vessels • Osteocyte = bone cells • Bone matrix = hard calcium-based material between cells Fig 7. 3
Tissue Types – Compact Bone Functions üHard and provides stability, framework, protection Structure üMatrix has hard mineral structure, based on calcium üCells and matrix are arranged in regular, concentric pattern Compact Bone
Tissue Types – Spongy Bone Functions üLightens total bone weight and provides space for bone marrow Structure üMatrix is softer mineral, less organized and less of it üEmpty spaces between matrix structure are filled with bone marrow Spongy (cancellous) Bone
Spongy Bone
Tissue Types – Hyaline Cartilage Functions üProvides soft and smooth covering to end of bone (articular surface) üHelps provide smooth and easy movement between bones (at joints) üProvides the starting material for new bone growth Structure üMatrix is gelatinous with fibers and is evenly distributed between the cells üCells (chrondocytes) are found in pairs within capsules called lacunae Hyaline Cartilage
Bone Physiology Living bones perform the following processes: • Formation • Starts as an embryo, continues through fetal development and after birth • Growth • Occurs from before birth through maturity • Remodel • Old matrix is removed and replaced with new matrix • Repair • Damaged bones will heal and return to normal structure
Bone Physiology – Formation
Bone Physiology – Formation • Fetal bones are made of hyaline cartilage • As cartilage cells die, they are replaced with spongy bone in diaphysis • After birth, spongy bone invades diaphysis • Compact bone replaces spongy bone in diaphysis • Hyaline cartilage remains on epiphyseal surface and in growth plate Fig 7. 5
Epiphyseal plate -cartilage band indicates ossification is occurring and spongy bone is being deposited
X Ray in Newborn
Bone Physiology - Repair • Hemotoma, a mass of clotted blood, forms at the fracture site. • A fibrous callus forms, and cartilage matrix is secreted. • Spongy bone forms to replace cartilage. • Bone remodeling occurs to remove excess material and replace compact bone.
Bone Physiology - Remodeling ü Bone matrix is inorganic and breaks down over time ü Specific bone cells (osteoclasts) remove old, broken matrix ü Other bone cells (osteoblasts) re-make/deposit new matrix ü The entire skeleton is remodeled every 7 -10 years ü Remodeling slows with age, elderly people have thinner bones and are more susceptible to broken bones as a result
Aging and Bone Tissue • There are two principal effects of aging on bone tissue: 1) Loss of bone mass • Results from the loss of calcium from bone matrix • The loss of calcium from bones is one of the symptoms in osteoporosis 2) Brittleness • Results from a decreased rate of protein synthesis • Collagen fibers gives bone its tensile strength • The loss of tensile strength causes the bones to become very brittle and susceptible to fracture
Osteoporosis
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