There are four major types of tissues in multicellular animals:
1. Epithelial tissues: Protective and covering tissues.
2. Connective tissue: Connecting, packing and supporting tissues.
3. Muscular tissue: Contracting & relaxing tissues, carrying movements of various organs.
4. Nervous tissue: Conducts impulses between brains and other organs.
Depending on the shape and function of the constituent cells.
Epithelial tissue is classified as follows:
Epithelial Tissue: Epithelium forms the outer protective covering all over the body, and lies inside all the cavities such as those of the mouth, throat, stomach, intestines, windpipe and lungs. The epithelial cells lie close together with little or no intercellular substance or matrix between them. There is no blood or lymph supply. Nerve supply is present. Epithelial cells are attached to the underlying tissues by a basement membrane, which is made of a network of white, non-elostic collagen fibres. Epithelium may be one-cell thick, that is, single layered or it may be several cell thick, that is many-layered.
Types of Epithelial Tissues:
1. Squamous
2. Columnar
3. Cuboidal
4. Ciliated
5. Glandular
6. Sensory
7. Stratified
Connecting tissue: Connective tissue is the supporting and binding tissue in animals. It supports and packs different tissues and organs together. Connective tissue is characterised by the presence of a large amount of non-living matrix, in which cells are embedded. It produces the matrix, ingest bacteria and produce certain proteins. Matrix is made of semifluid, rigid or gelatinous substances. Fibres are white collagen fibres and yellow elastin fibres.
Connective tissue is of the following types:
Muscular tissue:
a. The contractile tissues are made of muscle cells, which are elongated and large sized and are so, called muscle fibres.
b. These tissues help in various types of movements of body parts and locomotion.
c. On the basis of their location, structure and function, they are of three types:
1. Striated, muscles,
2. Unstriated muscles,
3. Cardiac muscles
(1) Striated muscles: They are attached to the bones and help in body movement and so, called skeletal or striated muscles. The striated muscle cells are long or elongated, cylindrical, unbranched and multinucleate. These muscles provide the force of locomotion and all other voluntary movements of the body.
Since the entire muscle fibres show alternate dark and light bands or stripes or striations, they are called striped muscles. These muscles work according to our will, so they are also called voluntary muscles. Their nuclei are peripheral in position. Striated muscles occur in muscles of limbs, body wall, face, neck, etc.
(2) Unstriated muscles: They occur as bundles or sheets of elongated spindleshaped cells or fibres, with a single centrally located Eiger shaped nucleus, in the centre of cytoplasm or sarcoplasm and contractile threads called myofibrils, which run longitudinally through the cell. Since the fibrils do not bear bands or striations, hence they are smooth muscles. These muscles do not work according to our will, so, they are called involuntary muscles. Smooth muscles control the movement of food in the alimentary canal or the contraction and relaxation of blood vessels. They are also found in the iris of the eye, in the uterus, and in the bronchi of the lungs.
(3) Cardiac muscles: This type of muscle tissues are present in the muscles of the heart and are composed of branched, cylindrical and uninucleate cells. Cardiac muscles show rhythmic contraction and relaxation of the heart and help to pump and distribute blood to various parts of the body.
(d) Muscles contain special proteins called contractile proteins, which contract and relax, to cause movement.
(e) The movement of internal organs, such as heart and alimentary canal, are all caused by muscular tissues.
Nervous tissue: The cells of nervous tissue are highly specialised for being stimulated and transmitting the stimulus very rapidly from one place to another within the body. The brain, spinal cord and nerves, all are composed of the nervous tissue. The cells of this tissue are called neurons or nerve cells. Each neuron has three parts i.e. the cyton or cell body, Nucleusdendrites and the axon.
(i) Cyton: It is the cell body of a nerve cell that has a large central nucleus and cytoplasm, from which long, hair-like parts arise.
(ii) Dendrite: These are the short branched fibre of neuron, which receives nerve impulses.
(iii) Axon: It is the single long conducting fibre extending from a neuron, that transmits impulses away from the cell body,
