How does bone develop Ossification the formation of

How does bone develop? Ossification - the formation of bone in two distinct ways: 1. Intramembranous ossification - bone development between sheets of embryonic membranes; used in flat bones of skull, in mandible, and clavicle 2. Endochondral ossification – cartilage is replaced by bone; used by all other bones

How does intramembranous ossification occur? 1. Precursor cells transform into osteoblasts • Secrete collagen and mineral salts 2. Osteoblasts cluster and secrete matrix around themselves 3. Plates form and interconnect = Spongy Bone 4. Osteoblasts cement themselves = osteocytes in lacunae 5. Membrane surrounding the bone = periosteum • The osteoblasts secrete compact bone over the new spongy bone --Bones that are formed this way = skull, mandibles, and clavicles

How does endochondral ossification occur? 1 st Cartilage model – chondrocytes lay down hyaline cartilage in the shape of the future bones 2 nd Bone collar formation – osteoblasts secrete bone matrix and results in a collar made of compact bone 3 rd Primary ossification center – osteoblasts are brought towards the interior by blood and lay down spongy bone --blood vessels in this area cause chondroblasts to die and become osteoblasts --this death causes the cavity to form--the Primary Ossification Center

How does endochondral ossification occur? 4 th Secondary ossification sites – central cavity expands, more blood vessels penetrate and the 2 nd site forms --osteoblasts in new periosteum create compact bone --ossification continues until spongy bone fills epiphyses and compact bone surrounds the whole structure 5 th Epiphyseal plate – a cartilage band that acts as a growth plate that allows bones to lengthen

Visualizing endochondral ossification

How do bones lengthen? • • Endochondral Bone Increases in length and width Length • Interstitial Growth @ Epiphyseal Plate (growth plate) • When chondrocytes are active, the side closer to the epiphysis will regenerate • The side near the diaphysis will become bone • Controlled by DNA and hormones Line of ossification = epiphyseal line

How do bones lengthen? • • • Endochondral Bone Increases in length and width Width • Appositional Growth • Osteoblasts in periosteum deposit new compact bone on diaphysis • Medullary cavity in the center expands • Destruction by osteoclasts • Usually unequal→ more deposited than removed

Bone Growth Flowchart Read the sections on endochondral and intramembranous bone development on page 158. Create a detailed flowchart (words and/or pictures) from the text.

Bone Growth Flowchart --here’s an example without diagrams or details --there should be diagrams and details on yours : )

How do hormones affect bone growth? • Growth hormone (GH) – stimulates general bone growth and the epiphyseal plates • Sex hormones – increases growth during adolescence • Vitamin D – converted to a hormone to allow calcium absorption in the intestine Seniors can tell us all about how hormone changes can result in various forms of gigantism. . .

What is bone remodeling and what is its role in homeostasis? • Bone remodeling – bone renewal at a rate of up to 18% per year • Remodeling allows bones to respond to stress • Homeostasis--adding/removing minerals from the blood – Regulates the calcium in the blood through hormones: • Parathyroid hormone (PTH) – increases blood calcium by accelerating bone recycling • Calcitonin – decreases blood calcium • Repair damage from disease or fracture Which type of bone cell is responsible for this? ?

Check out the animation! • https: //www. youtube. com/watch? v=0 d. V 1 B we 2 v 6 c

11. 2 Bone growth, remodeling and repair Health focus: Osteoporosis • Osteoporosis – bones are weakened due to a decreased bone mass • Bone reabsorption exceeds absorption usually by age 40 • Risk factors: women, white or Asian, thin, family history, early menopause, smoking, diet low in calcium, excessive caffeine or alcohol consumption and a sedentary lifestyle • Can lead to fractures and other complications • Can be treated with drugs, hormones and lifestyle change

11. 2 Bone growth, remodeling and repair Steps in bone repair • Hematoma (6 -8 hrs. ) – blood clot formed between broken bones • Fibrocartilaginous callus (~ 3 weeks) – cartilaginous callus forms between broken bones • Bony callus (3 -4 months) – cartilaginous callus is turned to bone • Remodeling – old bone tissue is replaced by new bone tissue

11. 2 Bone growth, remodeling and repair Bone repair