Bone Development and Growth (Ossification) - Anatomy and Physiology
- What are the zones of the epiphyseal plate, from the epiphyseal side toward the diaphysis?
- Resting (reserve), proliferation, hypertrophy, calcification, and ossification.
- A genetic disorder impairs chondrocyte proliferation at growth plates, causing short limbs but a normal skull vault. Which process is affected?
- Endochondral ossification. Intramembranous ossification of the skull vault is spared, as in achondroplasia.
- Where do the primary and secondary ossification centers of a long bone form?
- The primary center forms in the diaphysis; secondary centers form in the epiphyses, mostly after birth.
- In one epiphyseal plate zone, chondrocytes are greatly enlarged and the matrix begins to calcify. Which zone is this?
- The zone of hypertrophy (hypertrophic zone), where chondrocytes enlarge before the matrix calcifies and they die.
- How do long bones grow in length and in width?
- Length by interstitial growth of cartilage at the epiphyseal plate; width by appositional growth, with osteoblasts under the periosteum adding bone.
- What are fontanelles?
- Fibrous membrane-covered gaps between infant skull bones where intramembranous ossification is not yet complete.
- What is intramembranous ossification?
- Bone formation directly from mesenchyme, without a cartilage model. It forms the flat bones of the skull, the mandible, and most of the clavicle.
- What is endochondral ossification?
- Bone formation in which a hyaline cartilage model is replaced by bone. It forms most bones below the skull, including long bones.
- Which hormone is the main driver of bone growth in length during childhood, and through which mediator?
- Growth hormone, acting largely through insulin-like growth factor 1 (IGF-1) made by the liver.
- By which type of ossification does the parietal bone form?
- Intramembranous ossification, like the other flat bones of the skull vault.
- Which hormone causes closure of the epiphyseal plates at the end of puberty in both sexes?
- Estrogen. In males, testosterone is converted to estrogen, which closes the plates.
- What is the epiphyseal line?
- The bony remnant of the epiphyseal plate after it ossifies when growth in length ends.