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bone tissue

bone tissue under a microscope
 
Bone tissue (textus osseous) is well represented in the human body. Bone tissue performs several important functions: mechanical, supporting, participating in forming the systems of organs of movement. It is a depot of mineral salts, creates functional conditions within the red bone marrow. Bone tissue consists of , cells and intercellular substance as well as other types of connective tissues. The firmness of bone tissue depends on the fact that the intercellular substance is strongly mineralized by the salts of calcium, magnesium and fluoride which are deposited in the form of crystals.
 
Bone cells are osteoblasts. There are basophilic stained cells that are involved in the formation of bone tissue. There are also osteoclasts that are involved in bone destruction and osteocytes - the main bone cells. Osteocytes form the bulk of bone tissue.
 
There are two types of bone tissues: coarse-fibered (textus osseus reticulofibrosus) and laminated (textus osseus lamellaris). Coarse-fibered bone tissue does not show any special arrangement of osteocytes and fibers of intercellular substance. This type of bone tissue is represented in the embryonic stage of humans, adults have it in places of attachment of tendons to bones. The laminated bone tissue is widespread in humans. The structural unit of a laminated bone is a bone plate, in which parallel arranged collagen fibers are fused by mineralized primary substance.
 
There are osteocytes within or between the bone plates. Lamellar bone tissue forms two types of bone material: compact and spongy. In sponge lamellae bone plates form crossbars, connected among themselves. This substance is widely represented in the epiphysis of long tubular bones. In the compact substance  lamellae form three layers: 1. Outer layer of master plates 2. mesosteal middle layer 3. inner layer of master plates. Mesosteal layer is represented by osteons and systems of intercalary plates. Osteons are structural and functional units of the compact substance of tubular bones, providing a special strength. In the center of osteons there are blood vessels. Around these blood vessels there are concentric lamellae. In neighboring plates the collagen fibers have shifted chaotic direction, which provides strength to osteons. Channels of osteons connect with each other, forming the so-called perforating nutrient channels.

The bone surface is covered with periosteum, formed mainly of dense fibrous connective tissue, distinguishing 2 layers: external layer and internal fiber.

Vessels and nerves stretch from Periosteum into the bone. By means of vessels and nerves, periosteum is involved in the trophic, growth and regeneration of the bone. Medullary canal is lined with thin but strong connective plate - endosteum.
 

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