Animal Tissues

Based on their functions, animal tissues can be classified as:

1. Epithelial Tissue
2. Connective Tissue
3. Muscular Tissue
4. Nervous Tissue

Epithelial Tissues:

• 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:

1. 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.
2. Stratified squamous epithelium – They are arranged in a pattern of layers to prevent wear and tear. They are found in the skin.
3. Columnar epithelium – It is tall, pillar-like epithelium. It is present in the inner lining of intestines.
4. Ciliated Columnar Epithelium – Some columnar epithelial tissues have hair like structures called cilia. The movement of cilia can move mucus.
5. Cuboidal Epithelium – It has cube shaped cells. It forms the lining of kidney tubules and ducts of salivary glands.
6. Glandular Epithelium – Sometimes, a portion of the epithelium tissue folds inward, and a multicellular gland is formed. This is known as ‘Glandular Epithelium’.

Connective Tissue:

• 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:

1. Blood – It has a fluid matrix called plasma. Plasma contains salts, proteins and hormones.
2. Bone – It is strong and non-flexible. The cells are embedded in a hard matrix made up of calcium and phosphorous.
3. Ligament – It is elastic and has considerable strength. It contains very little matrix.
4. Tendons – It is fibrous tissue with great strength but limited flexibility.
5. Cartilage – It is a solid matrix composed of proteins and sugars.
6. Areolar connective tissue – It fills the space inside the organs, supports internal organs and helps in repair of tissues.
7. Adipose tissue – The cells are filled with fat globules.

Muscular Tissue:

• 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:

1. Striated Muscles – The cells are long, cylindrical, unbranched and multinucleate. They are also called voluntary muscles or skeletal muscles.
2. Unstriated Muscles – The cells are long with pointed ends and uninucleate. They are found in iris, ureters, bronchi of the lungs, etc.
3. Cardiac Muscles – These are found in heart. These heart muscles are cylindrical, branched and uninucleate.

Nervous Tissues:

• 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.