Bone Formation, Growth, and Remodeling

Ossification Ossification – Process of bone formation Steps in Ossification 1) Hyaline cartilage is used to form a model 2) Hyaline cartilage model is covered with bony matrix by osteoblasts 3) The enclosed hyaline cartilage is digested away - This accounts for the medullary cavity

Bone Remodeling Cells Osteoblasts - Bone forming cells that secrete the matrix - These are the cells responsible for making bone and storing minerals B for blast, B for build

Bone Remodeling Cells (Cont.) Osteoclasts – Giant bone destroying cells - Break down the matrix to release calcium

Appositional Growth This is how bones widen as they grow longer Steps in Appositional Growth 1) Osteoblasts in the periosteum add bone to the external face of the diaphysis 2) Osteoclasts in the endosteum remove bone from the inner face of the diaphysis

What controls the process of long bone growth? Human Growth Hormone – Secreted by the pituitary gland Sex Hormones – Testosterone and Estrogen Bone growth ends during adolescence when the epiphyseal plates are converted to bone

Regulating Blood Calcium When blood calcium drops: Parathyroid releases parathyroid hormone – This stimulates osteoclasts to destroy bone matrix to release calcium into the blood When blood calcium is too high: It is called hypercalcemia – Calcium is deposited in the matrix as calcium salts

What is Ricket’s? Disease in children in which the bones fail to calcify and harden Can be recognized by bowed legs Due to a lack of calcium and/or vitamin D

Fractures Simple Fracture – The bone breaks cleanly but does not penetrate the skin

Fractures (Cont.) Compound Fracture – Broken bone end sticks out of skin - Can easily become infected if not handled properly

Bone Fractures The bone breaks into many fragments Comminuted Fracture The bone breaks into many fragments Common in older individuals because their bones are brittle

Bone Fractures (Cont.) Compression Fracture – The bone is crushed Common in porous bones Example: Vertebrae

Bone Fractures (Cont.) Depressed Fracture – Broken bone portion is pressed inward - Typical of a skull fracture

Bone Fractures (Cont.) Impacted Fracture – The bone ends are forced into each other Common when breaking a fall

Bone Fractures (Cont.) Spiral Fracture – Very ragged fracture that occurs from excessive twisting Common sports fracture

Bone Fractures (Cont.) Greenstick Fracture – The bone breaks incompletely, like a green twig Common in children

Reduction of Fractures Open Reduction Open Reduction – Surgery is performed and the bones are pinned or screwed into place Closed Reduction – Doctor sets the bone with his hands Closed Reduction

Repairing Bone Fractures 1) A hematoma (blood filled swelling)is formed due to blood vessels being damaged during break. 2) The break is splinted by a fibrocartilage (soft) callus. This callus is composed of various connective tissue and functions to keep the break stabilized. 3) The bony callus forms. This callus replaces the fibrocartilage callus with spongy bone. 4) Bone remodeling occurs. The bony callus is remodeled to form a strong permanent patch at the fracture site.