Based on their functions, animal tissues can be classified as:
- Epithelial Tissue
- Connective Tissue
- Muscular Tissue
- Nervous Tissue
- They are the covering or protective tissues in the animal body.
- It covers most of the organs and cavities in the animal body.
- It also forms a barrier to keep the organs separate.
- The skin, the lining of mouth, the lining of blood vessels, lung alveoli and kidney tubules are made up of epithelial tissues.
- They are tightly packed with almost no intercellular space between them.
Based on their functions, different epithelia show different structures. They can be classified as:
- Simple squamous epithelium – It is a simple flat kind of epithelium. It is found in cells lining blood vessels, lungs alveoli, lining of mouth and oesophagus.
- Stratified squamous epithelium – They are arranged in a pattern of layers to prevent wear and tear. They are found in the skin.
- Columnar epithelium – It is tall, pillar-like epithelium. It is present in the inner lining of intestines.
- Ciliated Columnar Epithelium – Some columnar epithelial tissues have hair like structures called cilia. The movement of cilia can move mucus.
- Cuboidal Epithelium – It has cube shaped cells. It forms the lining of kidney tubules and ducts of salivary glands.
- Glandular Epithelium – Sometimes, a portion of the epithelium tissue folds inward, and a multicellular gland is formed. This is known as ‘Glandular Epithelium’.
- The cells are loosely packed and embedded in an intercellular matrix.
- The matrix can be jelly like, fluid, dense or rigid.
- The nature of matrix depends on the function of that particular connective tissue.
Connective Tissues can be classified as:
- Blood – It has a fluid matrix called plasma. Plasma contains salts, proteins and hormones.
- Bone – It is strong and non-flexible. The cells are embedded in a hard matrix made up of calcium and phosphorous.
- Ligament – It is elastic and has considerable strength. It contains very little matrix.
- Tendons – It is fibrous tissue with great strength but limited flexibility.
- Cartilage – It is a solid matrix composed of proteins and sugars.
- Areolar connective tissue – It fills the space inside the organs, supports internal organs and helps in repair of tissues.
- Adipose tissue – The cells are filled with fat globules.
- It consists of elongated cells called muscle fibres.
- Muscles contain special proteins called contractile proteins, which contract and relax to cause movement.
Types of Muscular Tissues:
- Striated Muscles – The cells are long, cylindrical, unbranched and multinucleate. They are also called voluntary muscles or skeletal muscles.
- Unstriated Muscles – The cells are long with pointed ends and uninucleate. They are found in iris, ureters, bronchi of the lungs, etc.
- Cardiac Muscles – These are found in heart. These heart muscles are cylindrical, branched and uninucleate.
- The cells of these tissues are called nerve cells or neurons.
- A neuron consists of nucleus and cytoplasm.
- Each neuron has a single, long part called axon and many branched parts are called dendrites.
- The brain, spinal cord and nerves are composed of nervous tissues.
- They are specialised in responding to stimuli.