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| Supporting Tissue |
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| It is a type of connective tissue in which the matrix is hard and rigid due to the presence of inorganic salts. The matrix encloses few cells. Fibres may be present or absent. It is also known as skeletal tissue since it forms the internal supporting framework (endoskeleton) of the body. |
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| Based on the components of matrix, supporting tissue can be classified into |
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| 1. Cartilage |
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| 2. Bone |
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| It is a type of supporting tissue in which the matrix is characterized by more of organic substances (nearly 85%). The rigid, homogenous matrix is known as chondrin. It lies enclosed in a fibrous connective tissue covering called perichondrium. Chondrin encloses numerous spherical or oval spaces called lacunae. Each lacuna contains either 1 or 2 or 4 cartilage cells or chondriocytes. These cells are capable of limited mitotic divisions. Fibres may be present or absent. |
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| fig. 5.65 White Fibrous Cartilage |
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| Based on the composition of matrix, cartilage can be distinguished into the following types: |
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 Hyaline cartilage: is the simplest and the most common type of cartilage. It has a rigid, homogenous matrix called chondrin enclosed in a fibrous membrane called perichondrium. Fibres are absent. The matrix contains numerous spherical or oval spaces called lacunae, which encloses either 1 or 2 or 4 chondriocytes. |
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| Hyaline cartilage is found forming the entire endoskeleton in the embryonic stage. In adults, it occurs in the wall of the larynx and trachea. |
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| fig. 5.66 Hyaline Cartilage |
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 Fibrous cartilage is a modification of hyaline cartilage in which the matrix contains white fibers. Hence, the cartilage attains more of rigidity. |
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| It is found forming intervertebral discs between the vertebrae. It also occurs at the joints between bones. |
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 Elastic cartilage is a modification of hyaline cartilage in which the matrix has yellow fibres. Hence, the cartilage attains elasticity. |
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| fig. 5.67 Elastic Cartilage |
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| Elastic cartilage forms a flap called epiglottis in the throat. It is also present in the pinna or external ear. |
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 Ossified or calcified cartilage is a modification of hyaline cartilage in which the matrix is deposited with calcium salts particularly, calcium phosphate. Hence, the cartilage attains hardness almost equivalent to that of a bone. Ossified cartilage occurs in the nose tip and at some bone joints like pubic symphysis. |
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| It is a type of supporting tissue in which matrix is hard and solidified due to the presence of more of inorganic substances. The inorganic salts in the matrix account for nearly 60% of the total chemical composition. Among the inorganic salts, calcium phosphate accounts for about 80% calcium carbonate for about 15% and the remaining 5% is represented by magnesium salts. The hard, solid matrix of bone is called ossein. It is normally found occurring in the form of concentric rings called lamellae. The lamellae enclose spaces called lacunae in which one or tiny osteocytes are present. Bones form the adult endoskeleton in the case of all vertebrates except the cartilaginous fishes. In the endoskeleton of a vertebrate, normally four types of bones can be recognized long bones, short bones, flat bones and irregular bones. |
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| The long bones and short bones are hollow and contain a space called marrow cavity filled with a fluid called bone marrow. It is a haemopoetic fluid in which blood cells take their origin. The flat bones and irregular bones do not contain a cavity. |
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| A typical long bone such as femur (bone of the thigh) in a cross section shows two fibrous membranes - an inner endosteum and an outer periosteum. The endosteum surrounds the marrow cavity. The bone matrix is found deposited between the endosteum and periosteum. |
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| In case of mammals, the bone is composed of tiny structural and functional units called Haversian systems. A Haversian system has a central canal called Haversian canal, which encloses an artery, a vein and nerve. |
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| fig. 5.68 A. Bone in L.S. |
| B. Bone in T.S. |
| C. Haversian Systems |
| D. Osteocyte |
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| fig. 5.69 T.S. of Mammalian Dried Long Bone |
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| Surrounding the Haversian canal the bone matrix is deposited in the form of concentric rings called lamellae. The number of lamellae ranges from about 4 to 20. Each lamella encloses numerous oval spaces called lacunae. Each lacuna contains 1 or 2 leave cells called osteocytes. All the osteocytes are connected to one another and to the central Haversian canal by numerous fine hair-like projections called canaliculi. The osteocytes draw their nourishment from the Haversian canal through the canaliculi. The Haversian canals are interconnected to one another through a number of Volkmann's canals. |
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| fig. 5.70 Osteocytes |
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