Bone Ossification and Repair PDF

# Bone Ossification and Repair ## Learning Objective: By the end of this lecture, you will be able to: - Know the two ways of bone histogenesis (ossification). - Identify the different zones of the epiphyseal plate. - Enlist the factor affecting bone growth. - Enumerate the stages of bone healing...

# Bone Ossification and Repair ## Learning Objective: By the end of this lecture, you will be able to: - Know the two ways of bone histogenesis (ossification). - Identify the different zones of the epiphyseal plate. - Enlist the factor affecting bone growth. - Enumerate the stages of bone healing and repair. ## Bone Histogenesis [Bone formation] Bone can be formed in two ways: 1. **Intramembranous Ossification:** - _Occur_ in flat bones. - It starts in *a membrane* of embryonic mesenchymal tissue and ends by the formation of spongy bone. 2. **Endochondral [cartilaginous] Ossification:** - Occurs in long bone, short and irregular bones. - It occurs by replacement of a *preexisting model or template* of hyaline cartilage whose shape resembles the shape of the future bone to be formed. - Now, all the cartilage model is replaced by bone except in 2 regions: 1. **Articular cartilage** - never ossify throughout life. 2. **Epiphyseal plate** - responsible for growth of the length in bone - disappear in adulthood at 20 years hence, no further increase in length. ## Different Zones of the Epiphyseal Plate: Epiphyseal cartilage is divided into five zones starting from the epiphyseal side of cartilage: 1. Resting cartilage zone. 2. Proliferative cartilage zone. 3. Hypertrophic cartilage zone. 4. Calcified cartilage zone. 5. Ossification zone. Ossification of the epiphyses is complete at about 20 years of age. ## Factors Affecting Bone Metabolism and Growth ### a) Hormonal Factors: 1. **Calcitonin** - Synthesized by parafollicular cells of the thyroid gland, act to reduce calcium level in blood by inhibits the activity of osteoclasts. 2. **Parathyroid hormone** - Promotes osteoclastic resorption of the bone matrix and increase calcium in blood. 3. **Growth hormone** - Deficiency in growing years causes pituitary dwarfism. - Excess causes acromegaly in adults or gigantism in growing years. 4. **Thryoid hormone:** Deficiency in children, as in cretinism, is associated with dwarfism. ### b)Nutritional Factors: 1. **Calcium and phosphate:** - Deficiency leads to: - Incomplete calcification of bone matrix [rickets in children]. - Reduced bone density, increased liability to fractures [osteomalacia in adults]. 2. **Vitamin D:** rickets in children. 3. **Vitamin C:** Causes Scurvy [brittle bone]. ## Healing of a Bone Fracture This process includes four stages: 1. Hematoma formation 2. Fibrocartilaginous callus formation 3. Bony callus formation 4. Bone remodeling Stages 2 & 3 are considered the Reparative Phase. ## Reference: Junqueira's Basic Histology: Text and atlas, 13th Edition, 2013. Anthony L. Mescher