Animal tissues

ANIMAL TISSUES 

 In the bodies of animals, there are four major categories of tissues: 
epithelial tissue,
 connective tissue, 
muscle tissue, 
and nervous tissue 

Epithelial tissue

 Epithelial tissue covers the outside of the body and lines organs and cavities. The cells in this type of tissue are very closely packed together and joined with little space between them. Epithelial tissue helps to protect organisms from microorganisms, injury and fluid loss. These tissues are commonly classified on the base of the shape of the cells as well as the number of cell layers. Some types include: Simple Squamous 

Epithelium 

A single layer of tightly packed, flattened cells. Found in lining of air sacs of the lungs, heart and blood vessels etc. Allows diffusion and filtration. Simple Cuboidal Epithelium Consists of single layer of tightly packed, cube-shaped cells. Found in kidney tubules, ducts and small glands. Makes secretions and absorbs materials. 
 Simple Columnar Epithelium Consists of single layer of elongated cells. Found in the lining of digestive tract and gallbladder etc. Makes enzyme secretions. 

 Ciliated Columnar Epithelium 

A tuft of cilia is present at the top of each columnar cell. Stratified Squamous Epithelium Consists of many layers of flattened cells. Found in the inner lining of esophagus, mouth, and at the surface of 
 the skin. It Protects underlying tissues from abrasion. 
 We know that an animal's survival depends on its ability to respond appropriately to stimuli from its environment. This ability requires the transmission of information from one part of the body to another. Nervous tissue forms a communication system and performs this task. This tissue is mainly composed of nerve cells, or neurons, which are specialized to conduct messages in the form of nerve impulses. Nervous tissue is found in brain, spinal cord and nerves. Exercise does not increase the numbers of our skeletal muscle cells; it simply enlarges those already present. 

Muscle tissue

 Muscle tissue consists of bundles of long cells called muscle fibers. It is the most abundant tissue in a typical animal. The cells of this tissue have ability to contract. There are three kinds of muscle tissue in vertebrates i.e. skeletal muscles, smooth muscles and cardiac muscles. The skeletal muscles are voluntary in action i.e. their contraction is under the control of our will. The smooth and cardiac muscles are involuntary in action i.e. their contraction is not under the control of our will. 

 Nervous tissue 

An animal's survival depends on its ability to respond appropriately to stimuli from its environment. This ability requires the transmission of information from one part of the body to another. Nervous tissue forms a communication system and performs this task. This tissue is mainly composed of nerve cells, or neurons, which are specialized to conduct messages in the form of nerve impulses. Nervous tissue is found in brain, spinal cord and nerves.