Various organs of an animal body are made up of four types of animal tissues :
- Epithelial tissue,
- Muscular tissue,
- Connective tissue; and
- Nervous tissue
Classification of Animal Tissue
1. Epithelial Tissue: Epithelial tissue is made up of epithelial cells which form the protective cover of the body in the form of skin. These tissues act as a barrier between different organs so that they can function individually without any interruption. They play a significant role in the protection, secretion, filtration and adsorption process of the body. The lining of the mouth, blood vessels, lung alveoli, kidney tubules all are made up of epithelial tissue.
Epithelial tissues can be divided into different categories by:
- How many layer are there? and
- How they look?
On the basis of how they look, they can be divided as:
a) Squamous Epithelial Tissue: This name is derived from a Latin word ‘squama’ which means the scale of a fish. As the name suggests, it looks like a scale or a single thin line. They are soft in nature.
b) Cuboidal Epithelial Tissue: It is a type of epithelial tissue which consists of cuboidal cells.
c) Columnar epithelium tissue: It is a uni-layer epithelial tissue comprised of columnar cells.
By number of layers, they can be classified as:
I. Simple Epithelial Tissue: If there is only a single layer of tissue then it is a simple tissue. It can be further divided into:
- Simple squamous (a single layer of squamous cells)
- Simple columnar (a single layer of columnar cells)
- Simple cuboidal (a single layer of cuboidal cells)
II. Stratified Epithelial Tissue: If the tissues are made up of more than one layer then it is known as the stratified tissue. It can be classified as:
- Stratified Cuboidal:
- Stratified Squamous
- Pseudo Stratified Epithelium: These tissues do not look like a simple or stratified cells in appearance. In this, some of the cells are narrow at the top and wider at the bottom while some of them are narrow at the bottom and wider at the top. Hence, they are known as pseudo-stratified cells.
- Squamous tissues are found in the esophagus, lining of the mouth, blood vessels and lung alveoli where transportation of substances needs a permeable membrane.
- Cuboidal tissues are found where mechanical support is required. For example the lining of kidney tubules and the duct of salivary glands.
2. Muscular tissue: Muscular tissue is one of the four kinds of animal tissues found in the animal body. It is soft in nature and contains contractile protein which can contract and relax, due to which there is movement in various parts of the body. These muscles can be broadly divided into two types:
A. Voluntary muscles: These muscles help in voluntary actions.
Skeletal muscles: They are the most abundantly found tissue in the body. One of the interesting facts is that about 200 muscles of a human body are used to make a step. These are long, unbranched, cylindrical and multinucleated. When we look into the muscles through the microscope, we observe a band like structure. Hence, it is also known as striated tissue.
B. Involuntary muscles: These are the muscles which help in the spontaneous actions. For example : Iris movement in the eye and bronchi movement in the lungs.
- Smooth muscles: These tissues have non-striated structure. Hence called unstriated These are small sized, tapered, uni-nucleated tissues.
- Cardiac muscles: These muscles are striated in structure and are branched cylindrical and uni-nucleated tissue. They are found in the heart of living organisms.
3. Connective Tissue: It is another type of animal tissues. It connects, binds and supports various organs in the body. They include bones, blood, and fats.
a) Blood: Blood is the fluid that transports nutrients and oxygen to the cells of the body. It has two components namely:
- Plasma: Blood consists of a colorless fluid called plasma (contains water, proteins, salts, and hormones).
- Blood cells: Three types of blood cells are Red blood cell (RBC) or erythrocytes, white blood cell (WBC) or leukocytes and platelets or thrombocytes.
b) Bones: Bones are the living tissues that provide support and protection to various organs.
c) Fats: Fats are connective tissues specialized in insulation against cold and storage.
4. Nervous Tissues: Nervous tissue is the fundamental component of the peripheral nervous system and central nervous system. They consist of specialized cells called neurons and glial cells. Nervous tissues are specialized to transmit electrical impulses rapidly throughout the body. Hence, these animal tissues help us to react to stimuli like touch, sight, smell, and hearing.
Neurons play a significant role in the transmission of electrical impulses from the brain to the various organs of the body and vice-versa. Each neuron is separated from another neuron by a gap called synapse. A nerve cell consists of three parts namely cell body, dendrites, and axon. The cell body is bounded by the cell membrane and contains a nucleus. Dendrites are the short branched structure that receives impulses from a pre-synaptic neuron and transmits to the cell body. Axon is an extended projection in the neuron that carries impulses from the cell nucleus to post-synaptic neuron.
We had a brief description of animal tissues and their functions. To know more about them, watch the video.