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| Bone and Cartilage |
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| The skeletal tissue is characterised by dense and mineralised matrix. These form the supporting framework of the body and also protect the vital organs of the body. |
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| The skeletal tissue are of two types: |
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| a) cartilage |
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| b) bone |
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| Cartilage |
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| Cartilage or grisle as it is also called is a dense, clear blue-white substance, very firm but less firmer than bone. It is found principally at joints and between bones. |
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| The bones of the embryo are first cartilage, then the growing centres persist as cartilage, but in adults, it is found covering the bone ends. |
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| Cartilage does not contain blood vessels but is covered by a membrane perichondrium from which it derives blood supply. The cartilage consists of specialised cells called chondrocytes which are generally present in groups of 2-4 cells. Each cell lies in a fluid space called lacuna. |
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| There are 2 main varieties of cartilage: |
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| Hyaline cartilage |
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| This consists of collagen fibres embedded in a clear, glassy, tough ground substance called matrix. It is firm and elastic and is found covering the ends of the long bones as articular cartilage, in the nose, larynx, trachea and bronchial tubes where it keeps open the orifice. The cells of hyaline cartilage are arranged in small groups, set in a tough matrix. |
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| Fibrous cartilage |
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| Here the matrix contains large number of fibres. On the basis of type of fibres present, it is of 2 types. |
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| White fibro-cartilage(fibro cartilage) |
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| Here the small amount of matrix of cartilage is packed with large number of bundles of thick white fibres, and hence it the toughest, strongest and less flexible It has no perichondrium. It is found in intervertebral disc as shock absorber. |
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| Yellow fibro-cartilage (elastic cartilage) |
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| Here the matrix is packed with yellow or elastic fibres which run in all directions to form a network. It appears yellow and opaque. The presence of the yellow fibres makes it very flexible. It is found in the epiglottis, pinna of the ear, and at the tip of the nose. |
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| Bone |
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| Bone is the hardest connective tissue in the body. It is composed of nearly 50% water and the remaining solid part is composed of a mineral matter, mainly calcium salts and cellular matter. A bone is externally covered by a thick, white dense fibrous sheath called the periosteum. |
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| A long bone such as those of the limbs, shows both varieties of bone tissue. Longitudinally, it shows compactly arranged tissue. The bone is divided into shafts. If the shaft is cut across, a dense bone tissue which encloses a hollow cavity can be seen. This is called the marrow cavity or the medullary cavity. |
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| Marrow cavity is filled with a soft and vascular fatty tissue called bone-marrow which are of two types: red marrow and yellow marrow. The red bone marrow is highly vascular tissue and forms erythrocytes and granular leucocytes. |
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| Yellow bone marrow is mainly involved with the storage of fat. It also forms blood corpuscles only at the time of emergency. |
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| A transverse section of a compact bone shows a wonderful design mapped out in circles. In the centre of each circle is a haversian canal. The plates of bone or lamellae are arranged concentrically around the central canal. In between these plates are minute spaces called lacunae and these spaces contain bone cells and these spaces are connected to each other and to the central haversian canal by minute canals called canaliculi. Each pattern thus formed is a complete haversian system composed of a central haversian canal containing nerves, blood vessels and lymphatics, lamellae arranged concentrically, lacunae containing bone cells and canaliculi radiating between and linking up the lacunae and the haversian canals. |
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| The areas between these haversian systems are composed of interstitial lamellae. |
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