There are four types of tissues found in animals: epithelial tissue, connective tissue, muscle tissue, and nervous tissue.
Epithelial Tissue: The epithelial tissue forms the covering or lining of most of the organs. Permeability of the epithelial tissue plays a great role in exchange of materials among various organs. It also plays an important role in osmoregulation. Epithelial tissues are of 4 types:
a) Simple Epithelium: i) The simple epithelium is composed of a single layer of cells. ii) E.g. Lining of blood vessels and alveoli.
b) Cuboidal Epithelium: i) The cells are cube-shaped in cuboidal epithelium. ii) Lining of kidney tubules and ducts of salivary glands. iii) Provide mechanical support. iv) Play the role of secretion and are called glandular epithelium.
c) Columnar Epithelium: i) Cells are column-shaped in columnar epithelium. ii) Facilitates secretion and absorption. iii) E.g. lining of intestine iv)In some organs, columnar epithelium has cilia present on the outer surface.The ciliated epithelium in the respiratory tract pushes the mucus forward.
d) Stratified Epithelium: i) Cells of the stratified epithelium are in many layers. ii) Skin is an example of stratified epithelium. iii) Stratification of layers prevents wear and tear.
Connective Tissue: The cells of a connective tissue are loosely scattered in a matrix. The matrix can be a fluid, jelly like, dense or rigid. Following are the various connective tissues: a) Areolar Connective Tissue: i) Found between skin and muscles, around blood vessels and nerves and in bone marrow. ii) Fills the gap between tissues and provides support. iii) It also helps in repair of tissues.
b) Adipose Tissue: i) Adipose tissue is composed of fat globules.
ii) Found below the skin and beneath the organs.
iii) Provides insulation and works as a cushion.
c) Bone: i)Bone is mainly composed of osteoblasts. ii) Bone makes the skeletal system. iii) Responsible for providing structural framework to the body.
iv) It provides protection to important organs and facilitates movements.
d) Cartilage: i) Mainly composed of chondrioblasts. ii) Present at the ends of articulatory bones, external ear, bronchii etc.
e) Blood: i) Composed of blood cells, platelets and plasma. ii) Plays an important role in transportation of various substances in the body. iii) Also helps in osmoregulation and temperature control.
Muscular tissue is composed of muscle cells. Muscle cells are specialized cells which have the ability to contract and expand. Due to contraction and expansion, muscles facilitate various kinds of movements in the body. Muscular tissues are of three types:
1) Striated Muscles: The cells of striated muscles are in the form of long, unbranched fibres. 2) Smooth Muscles: The cells of smooth muscles are spindle shaped and each has one nucleus. 3) Cardiac Muscles: The cells of cardiac muscles are in the form of branched fibres.
Nervous tissue makes the nervous system and is composed of specialized cells called neurons. A neuron can be divided into two distinct parts, viz. head and tail. The head is somewhat star-shaped and contains nucleus and some other cell organelles. This is called cyton. There are numerous hair-like outgrowths coming out of the cyton. These are called dendrites. The tail ends in axon terminals. Dendrites receive the nerve impulse, while axon relays the nerve signals.