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Animal Tissue and its Type
Every animal, whether it is unicellular or multicellular, is capable of performing all vital functions such as respiration, ingestion, excretion and reproduction.
1.0Types of Animal Tissue
Based on the location and function, the animal tissues are classified into four types:
Epithelial Tissue, Muscular Tissue, Connective Tissue, Nervous Tissue
2.0Epithelial Tissue
Word epithelium is composed of two words Epi-upon, Thelio-grows. (Means - A tissue which grows upon another tissue is called epithelium).
Nature of Epithelial Tissue
It is the simplest tissue. It is the protective tissue of animal's body. It covers most organs and cavities within the body. It also forms a barrier to keep different body systems separate.
Epithelial cells are closely packed and have small amount of cementing material, so there are very little inter-cellular spaces present between the cells. Due to absence or less of intercellular spaces; blood vessels, lymph vessels and capillaries are unable to pierce this tissue, so blood circulation is absent in epithelium. Hence cells depend for their nutrients on the underlying connective tissue.
It always rest upon underlying connective tissue. At the junction of the epithelial tissue and connective tissue a layer is present which is called basement membrane (extra cellular fibrous), which is formed of mucopolysaccharides and collagen fibrils.
The epithelial tissue can be simple (single layered) or stratified (multilayered). Simple squamous epithelium forms the lining of blood vessels and alveoli of lungs. Stratified squamous epithelium is found in skin, buccal cavity and esophagus.
3.0Types of Epithelial Tissue
(on the basis of shapes and functions)
Squamous epithelium (scale like)
Squamous epithelial tissue is also known as pavement epithelium, as a compact structure gives an impression like tile on a floor.
Description: Flattened cells, extremely thin.
Common locations: Walls of blood vessel, air sacs of lungs, oesophagus, lining of mouth.
Function: Diffusion
Cuboidal Epithelium
Description: Cube like cells, may have microvilli at its free surface.
Common locations: Lining of kidney tubules, ducts of salivary glands. It also forms germinal epithelium of gonads.
Function: Secretion, absorption, mechanical support, excretion.
Columnar (Pillar like)
Description: Tall slender cells; may have microvilli at its free surface.
Common locations: Inner lining of intestine, part of respiratory tract lining.
Function: Secretion, absorption.
4.0Modification of Columnar Epithelium
Glandular Epithelium
Description: Tall, slender cells, some cells from the free surface invaginate inside to form secretory cells - goblet cells.
Common location: Lining of intestine & glands, trachea, bronchi.
Function: Secretion of mucus and other secretions.
Ciliated Columnar Epithelium
Description: Tall, slender cells which possess cilia.
Common location: Lines the nasal passages, oviducts, terminal bronchioles.
Function: Protection, movement of substances in a particular direction for e.g. of mucus in nasal passages, egg in oviduct.