Animal Tissue, Epithelial Tissue
A group of cells which has similar structure and performs a definite function is called the Tissue.
The outer layer of the body of an animal is covered by a protective tissue called epithelial tissue. The inner surface of the mouth, food pipe, stomach, intestine are also lined by epithelial tissue. This tissue consists of a single layer or many layers of cells. The cells in this tissue may be flat or pillar like or cube like or tubular in shape.
TThe connective tissue binds and connects the different tissues and organs together. It forms a package tissue around the organs. It protects blood vessels and nerves. The connective tissues are tendons, ligaments, cartilage, bone and blood.
This tissue is elastic. It helps in the movement of the body. They are classified in to voluntary, involuntary and cardiac muscles. Voluntary Muscles: These muscles are made up of elongated fibers and are generally found attached to the skeleton of the body in the form of bundles. These muscles are very strong and controlled by the will of the animal.
The involuntary muscle fibers are found in layers or bundles. They are found in the walls of the intestine, respiratory tubes, blood vessels, urinary tract and reproductive organs. These muscles are not under the control of the animal.
Cardiac muscle fibers are long, thread like and branched. These branches are connected to form a network. They are found in the heart and are responsible for rhythmic contraction and expansion of the heart.
As soon as we hear the sound of a horn, we move to one side. How is it possible? We respond to the external stimuli without our knowledge. There are many such reactions in our daily life. These are called stimulus response reactions. These are possible because of the presence of the nervous tissue in animals. The basic unit of nerve tissue is the nerve cell (neuron). In the animal world, man has highly developed nerve tissue. The nervous tissue helps the body to control and co-ordinate various activities.