BONE HISTOLOGY Histology of Bone Bone consists of
BONE HISTOLOGY
Histology of Bone � Bone consists of widely separated cells surrounded by large amounts of matrix � Four principal types of cells: 1. 2. Osteoprogenitor cells – multipotent stem cells that can turn into other bone cells. Osteoblasts – bone forming cells located in peri & endosteum. Synthesize collagen.
Histology of Bone � Osteocytes – mature bone cell (osteoblast surrounded by a calcium matrix). Maintain daily metabolism such as the exchange of nutrients and wastes with the blood. � Osteoclasts – cell that destroys or reabsorbs bone cells and are concentrated in the endosteum
Histology of Bone � Matrix contains some calcium carbonate, calcium phosphate but mostly hydroxyapatite, which is the PRIMARY salt that makes bone hard. � Matrix (Bone) composition = 25% water, 25% protein fibers and 50% minerals
What are the tissues that make up bones? 1. Compact Bone Tissue ○ Outer layer of bone ○ Dense in appearance ○ Made out of water, collagen, and crystalized mineral salts (Ca, P) 2. Spongy Bone Tissue ○ Inner layer of bone ○ Filled with red bone marrow ○ Arranged in bars and plates called Trabeculae ○ Porous openings between trabeculae = spongy appearance
What does compact bone look like at the microscopic level? � Matrix organized into structural units called OSTEONS � aka Haversian System � Circular and tubelike � Arranged into layers (rings) called lamellae � Lamellae are made up of protein fibers, calcium, phosphorus and other minerals � Lamellae surround central canal which contains blood vessels, nerves and lymph
What separates the Lamellae circles? � Rings of osteocytes (mature bone cells) � Osteocytes are found in spaces called lacunae � Tiny canals called canaliculi radiate outward from the central canal to all lacunae making them connected � Blood vessels and nerves enter central canal from periosteum
Bone Growth � Most bone is formed by Endochondral ossification (IN- outward) � Occurs in all bones except flat bones. �Step 1 = Cartilage forms �Step 2 = Cartilage grows �Step 3 = Bone replaces the cartilage from the inside center outward.
� Intramembranous � Within membranes, no cartilage precursor � Forms flat bones
Bone Repair
What is cartilage? • Special form of dense connective tissue that is comprised of collagen and elastin fibers. • Cartilage is created by chondrocytes. • No blood vessels so nutrients and waste are transported via diffusion. Very slowly.
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