The tissues in animals are of four types.
1. Epithelial tissue. 2. Connective tissue. 3. Muscular tissue. 4. Nervous tissue.
The structure of the cells varies according to their functions:
1. The epithelial tissue performs protection, excretion, secretion, sensation and absorption functions.
2. The connective tissue is the supporting and binding tissue.
3. Muscular tissue aids in contraction and movement of the body muscles.
4. Nervous tissue helps in coordination of different organs.
1. Epithelial tissueIt is a primitive type of tissue and derived from all the three germinal layers
i.e. from ectoderm, mesoderm and endoderm.It covers the other tissues and body,
forms the epidermis of skin. It forms outer and inner linings of all visceral organs and body cavity.
The cells are compactly packed with little intercellular matrix.
The cells are arranged in arrows.Based on the number of layers, the epithelial tissue is of two types.
They are
A. Simple epithelium - single row of cells.
B. Compound epithelium - more than one row of cells.
A. Simple epithelium:Based on structural modification of cells,
simple epithelium is further divided into three types:Simple squmous or squamous
-- Which is made up of a single thin layer of flattened cells with irregular boundaries.
They are found in the walls of blood vessels and air sacs of lungs
and are involved in a function like forming a diffusion boundary.Cuboidal epithelium
-- Which is composed of a single layer of cube like cells.
Commonly found in ducts of glands and tubular parts of nephrons in kidneys.
Main functions are secretion and absorption.Columnar epithelium
-- Which is composed of a single layer of tall pillar like cells.
Nuclei are located at the base. Free surface may have microvilli. Found in the lining of stomach
and intestine helps in secretion and absorption.
Ciliated columnar epithelium is composed of columnar cells
bears cilia on the cuboidal (or) columnar cells on their free surface.
These are useful to move particles or mucus in a specific direction over the epithelium
. Mainly present in the inner surface of hallow organs like trachea, bronchi,
genital ducts, brain ventricles, and
fallopian tubules
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