Essay on the Important Categories of Connective Tissue!
This tissue provides the structural framework and support to different tissues and helps in body defence, tissue repair, and fast storage. About 30% of body mass is formed of connective tissue. Connective tissue can be divided into two categories –
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I. Connective tissue proper
II. Skeletal tissue
III. Vascular tissues
I. Connective tissue proper:
Ground substance (matrix):
The ground substance occupies the space between the cells and fibres of connective tissues. It consists of mainly water and sulfated mucopolysaccharides.
Connective tissue cells:
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Fibroblasts – Which secrete fibres and some matrix.
Macrophages – Also called histiocytes. These are modified monocytes cells. Phagocytic in nature.
Mast cells – Store histamine (vasodilator), serotonin (vasoconstrictor) and heparin (anticoagulant). These take part in allergic reactions and also help in body defence. They secrete major part of the matrix.
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Lymphocytes – Migrating cells and transport antibodies.
Plasma cells – Derived from B-lymphocytes and produce antibodies against a specific antigen. They have a limited migratory ability and a short life.
Protein fibres:
Collagen fibres (most common fibre type) are white and have high tensile strength. Also laid down at sites of injury. It is formed of protein collagen which changes to gelatin on boiling.
Elastic fibres are yellow in colour and highly elastic, formed of elastin protein. These fibre are interwoven with collagen fibres in order to limit dispensability and to prevent tearing.
Reticular fibres form a network formed of reticulin protein. They provide a supporting framework for cellular constituents of various tissues and organ e.g. liver.
1. Loose or Areolar connective tissue:
With abundant ground substances and thin and relatively sparse fibres. It is found beneath the epithelia of skin, hollow visceral organs and on the walls of arteries and veins.
All cell types and fibres (discussed above) are present. The areolar tissue forms packing between different tissues. It protect and nourishes the organs and structures it bends and store body fluids.
2. Adipose tissue:
Main cells are fat cells or adipocytes which contain mainly fat. Adipose tissue occurs mainly beneath the skin in mesenteries, bone marrow and around kidneys and below liver. It prevents heat loss and forms shock absorbing cushions around kidneys and eye balls.
3. Dense connective tissue is of two types:
White fibrous tissue:
Only collagen fibres are present in the matrix and cells are mainly fibroblasts. It is present at the joints between skull bones and makes them immovable. Also found in the dermis of higher mammals. A tendon consists of parallel bundles of collage nous fibres between which are present rows of fibroblasts.
Yellow elastic tissue:
Mainly elastic fibres are present, so highly elastic. They are mostly present in ligaments wall of blood vessels, bronchioles and lungs.
4. Reticular connective tissue:
Ground tissue is lymph, branching reticular fibres of protein reticulin and all types of cells are present but macrophages predominate.
Most of the reticular tissue is specialised to synthesize white blood corpuscles. It is found in spleen, Peyer’s patches, bone marrow, lymph nodes, liver etc.
5. Mucous connective tissue:
A gelatinous substance called Wharton’s jelly is present in which few fibroblasts and collagen fibres are present. It is found in umbilical cord and vitreous humor.
6. Pigmented connective tissue:
Gives colour to the structures. They are found in the choroid culinary body, iris of the eye and dermis of the human skin.
II. Skeletal connective tissue (Supporting connective tissue):
Vertebrate body possesses a hard internal framework of endoskeleton, which is made up of supporting or hard connective tissue. It is of two types – cartilage and bone that provide the body with mechanical support and protection.
Cartilage:
Mesodermal cells called chondroblasts form cartilage (chondro genesis). Matrix consists of chondrin protein.
Cells are exclusively chondrocytes. Matrix (rich in proteoglycons consisting of core proteins) serves as the route for the diffusion of substances between surrounding blood vessels and chondrocytes.
Chondrocytes are present in groups of 2 or 3 cells in small spaces (lacunae). A sheath of collagen fibres, perichondrium, surrounds the cartilage. Cartilage is further divided into 3 types –
(a) Hyaline cartilage:
The matrix is fibreless and glass like. It is the initial skeleton of the foetus. In adult it is found in bronchi, larynx, and nasal septum, at the end of ribs, tracheal rings and at the articular surface of long bones.
Calcified cartilage:
This cartilage is formed by the calcification of hyaline cartilage (i.e. salts of calcium are deposited in the matrix). E.g., suprascapula of pectoral girdle and pubis of pelvic girdle in frog.
(b) Elastic cartilage (yellow elastic fibrocartilage):
Mainly elastic fibres are Perichondrium present in the matrix. It forms pinna of ear, tip of nose, eustachian tube and epiglottis.
(c) Fibrous cartilage:
Has characteristics intermediate between those of hyaline cartilage and dense connective tissues. Its presence indicates the need for resistance to compression and shear forces.
Thick dense bundles of collagen fibres are present between rows of chondrocytes. It is present in joints between vertebrae and at pubis symphysis (where it helps in parturition). Parturition refers to the act or process of giving birth to a child.