Osteocytes are found wthin lacunae they are cells

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Osteocytes are found wthin LACUNAE. They are cells that have long processes that run through the CANALICULI and come into close contact with those processes of other osteocytes. Diffusion of O2 and nutrients is possible. Mesenchyme cells osteochondral progenitor cells osteoblasts osteocytes 4. OSTEOCLASTS: thought to be derived from stem cells in the red bone marrow (not from the osteochondral progenitor cells in bone and cartilage). They will settle on surfaces of bone and are responsible for RESORPTION or breakdown of the matrix. This resorption of bone is important in the growth and repair of bone and is a natural process that is constantly occuring. In health, resorption is in balance with OSTEOGENESIS (formation of new bone by osteoblasts). These cells have many nuclei and have ruffled edges. What is the composition of bone matrix? The MATRIX of bone is solid, composed of 35% organic and 65% inorganic material. The organic material consists primarily of the protein collagen. The inorganic material is primarily of a calcium phosphate crystal called HYDROXYAPATITE. The collagen is responsible for flexibility and the inorganic material gives it strength. DIAPHYSIS: The shaft of the bone EPIPHYSIS: The extremities or ends of the bone. EPIPHYSEAL GROWTH PLATE growth area of bone. Originally hyaline cartilage. This area closes as person ages and is known as EPIPHYSEAL LINE. ARTICULAR CARTILAGE: thin layer of hyaline cartilage covering surface of bone where it meets another bone within a joint. Reduces friction. PERIOSTEUM: membrane around the surface of the bone, except where t here is articular surface. MEDULLARY CAVITY: space within the diaphysis that contains the yellow marrow and, in specific bones, red marrow. ENDOSTEUM: membrane lining of medullary cavity. BONE DEVELOPMENT:
The skeleton during early development, is composed of fibrous connective tissue and hyaline cartilage, not bone. As the embryo develops, bone will replace these 2 types of tissue. Ossification (production of bone tissue) begins at about 5 weeks gestation and continues throughout a person’s life. There are 2 types of ossification, based on the original tissue that the bone replaces – INTRAMEMBRANEOUS OSSIFICATION and ENDOCHONDRAL OSSIFICATION. 1. INTRAMEMBRANEOUS OSSIFICATION direct ossification a. At about 5-6 weeks of development, mesenchyme forms a fibrous connective tissue membrane around the brain and where the mandible and clavicles will be. b. These mesenchymal cells become osteochondral progenitor cells which then become osteoblasts. c. As the osteoblasts produce matrix, they differentiate into osteocytes due to a decrease in oxygen. Bone has been formed directly from mesenchyme, within a membrane. In humans, this type of ossification occurs only in the flat bones of the skull, mandible and clavicles.

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