Tissues
A tissue is an aggregation of cells that are similar in structure and function to perform a specific function. Intercellular substance and fibres are the non-living parts of a tissue. In between the cells is the intercellular substance, produced by the cells themselves. The intercellular substance generally consists of a homogenous ground substance or matrix. Fibres are embedded in the ground substance. The structure, shape, size, and arrangement of the cells, the bio-chemical and physicochemical properties of the ground substance, and the nature of fibres when present are different in the various types of tissues. Further the proportion between the cells and the intercellular substance also differs from one type of tissue to another. Different types of fundamental tissues are evolved in the body based on the basic property of the protoplasm to perform a specific function. The Organ (e.g. liver) is made-up of a combination of one or more of the fundamental tissues to perform a specific function. Several organs with a common function form the Organ System (e.g. digestive system) in the body. Different organ systems join to form the individual. There are four types of elementary or fundamental tissues in the animal body in the adult and the organ systems are made up of one or more of these varieties of tissues arranged in a specific and characteristic way in each organ. The elementary or fundamental tissues are,
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