Structure of an animal is formed with several kinds of cells. There are 200 different types of specialized cells in the human body. The cells of one or more kinds are arranged together in a characteristic manner and perform a specific role. Such a group of cells is called a tissue. The cell of a tissue may secrete between them as a non-living intercellular material. Thus, a tissue may be defined as a group of one or more types of cells having a similar origin and specialized for a specific function along with the intercellular material.
The tissues are classified into four groups on the basis their location and functions:-
1) Epithelial tissue
2) Connective tissue
3) Muscular tissue
4) Nervous tissue
- Epithelial tissue:
It is a tissue composed of one or more layers of cells that cover the body surface and lines its various cavities. It is used for protection, secretion, and excretion. The word ‘epithelium’ was introduced by Ruysch.
(i) Simple epithelium: It is formed by single layer cells.
(1) Simple squamous epithelium: It is consists of only one layer of flat, scale-like cells, usually polygonal cells which are closely fitted together like the tiles of a mosaic. It is also known as pavement epithelium.
(2) Simple cuboidal epithelium: The simple cuboidal epithelium is composed of one layer of cuboidal-shaped cells resting on a basement membrane. The nuclei are situated centrally.
(3) Simple columnar epithelium: It consists of a single layer of cells, many of which have modified structure. Three common modifications are the goblet, cilia, and microvilli.
(4) Simple ciliated epithelium: It bears numerous delicate hair-like outgrowths called cilia arising from basal granules helps to create a current to transport the materials.
2. Connective Tissues
It greatly connects and supports all the other tissues, the intercellular element predominating. The cellular element is usually scanty. It is made up of matrix and living cells that connect and support different tissues. Connective tissue was called mesenchyme by Hertwig (1893).
It provides support and surface for attachment of muscle. Skeletal connective tissues form the framework of the body. It provides rigidity to the body. These protect the various organ and help in locomotion. It is divided into three types.
(i) Cartilage: Cartilage is a solid but semi-rigid and flexible connective tissue. Cartilage is a nonvascular connective tissue, consisting of cells embedded in a resilient matrix of chondrin.
(ii) Bone: Bone is a highly calcified (mineralized), hard and rigid connective tissue. It is the major component of adult vertebrate endoskeleton. Besides its mechanical function of supporting the body architecture and internal organs as a framework, of protecting delicate organ like brain, heart, etc. of forming to muscles to facilitate movement and locomotion
- Muscle Tissues:
These are soft tissues which compose muscles in animal bodies. The cells of Muscle tissues are called as myocytes.
- Nervous Tissues:
Nervous tissues cells are specialized for receiving stimuli and transmitting messages