Notes
Bone tissue and growth
- Bones support, protect, allow movement, store minerals and fat, and produce blood cells in red marrow. A long bone has a diaphysis, epiphyses, periosteum and medullary cavity.
- Compact bone has osteons; spongy bone has trabeculae. Osteoblasts build bone, osteocytes maintain it and osteoclasts resorb it.
- Bone lengthens at the epiphyseal plate. PTH raises blood calcium by activating osteoclasts. Fractures heal through hematoma, fibrocartilage callus, bony callus and remodeling.
The skeleton
- The axial skeleton (80 bones) has the skull, vertebral column (7 cervical, 12 thoracic, 5 lumbar, sacrum, coccyx) and thoracic cage.
- The appendicular skeleton (126 bones) has the pectoral girdle, pelvic girdle and limbs.
Joints
- Fibrous, cartilaginous and synovial joints. Synovial joints have a cavity, articular cartilage and synovial fluid. Ball-and-socket joints move most freely; hinge joints move in one plane. Ligaments join bone to bone; tendons join muscle to bone.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Osteoblasts secrete bone matrix. Osteoclasts resorb it.
The scapula is part of the pectoral girdle. The sternum, mandible and vertebrae are axial.
Vitamin D is needed for calcium absorption. Deficiency in children causes rickets.
The hip and shoulder are ball-and-socket joints with the greatest range of motion.
Open epiphyseal plates are the sites of longitudinal growth and are vulnerable to injury.
Ligaments join bones across a joint. Tendons attach muscle to bone.
Free response
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Free-response question
A 70-year-old woman slips and fractures her hip. Her doctor says she has osteoporosis. A 14-year-old boy, in contrast, is growing about 8 cm a year and often breaks no bones.
(a) Describe what happens in osteoporosis in terms of the activities of osteoblasts and osteoclasts.
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Bone resorption by osteoclasts exceeds bone formation by osteoblasts, so bone mass and density decrease and bones become fragile.
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(b) Name the region of a long bone where the boy's height increase occurs and explain how it works.
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Growth occurs at the epiphyseal plates (growth plates). Cartilage cells divide and are replaced by bone, which lengthens the shaft until the plates close.
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(c) Give one lifestyle recommendation for bone health and explain why it helps.
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Weight-bearing exercise and adequate calcium and vitamin D. Mechanical stress stimulates bone formation, and calcium and vitamin D supply the minerals needed for matrix.
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