Anatomy and Physiology / Unit 4: The Skeletal System
4.3 Bone Growth, Remodeling and Repair
Notes
Bones form by ossification. In intramembranous ossification (most skull bones, clavicle) bone forms directly from membrane. In endochondral ossification (most other bones) a hyaline cartilage model is replaced by bone.
- Lengthwise growth occurs at the epiphyseal plate (growth plate) until it closes in the late teens to early twenties; thickness grows by appositional growth under the periosteum.
- Remodeling continues throughout life. Calcium homeostasis: low blood calcium makes the parathyroid glands release parathyroid hormone (PTH), which stimulates osteoclasts to release calcium. Calcitonin can lower high blood calcium.
- Weight-bearing exercise strengthens bone. Osteoporosis is loss of bone mass (common in postmenopausal women).
- Fracture repair: hematoma, fibrocartilage callus, bony callus, then remodeling.
- Vitamin D is needed to absorb calcium; rickets in children is soft bone from vitamin D deficiency.
Practice
Blood calcium falls below normal. Which response restores it?
PTH raises blood calcium by increasing bone resorption by osteoclasts.
A 12-year-old's femur is increasing in length. Growth is occurring at the:
Cartilage in the growth plate is replaced by bone, lengthening the shaft.
Which is the correct order of events in healing of a fracture?
A blood clot forms first, then soft callus, then hard callus, then remodeling.
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