What are Tissues?
Cells are the basic structural and functional units of all living organisms. Tissues are groups of cells, which are similar in structure and perform a specific function. Each organ is made up of various tissues, and many organs together coordinate and constitute the organ system.
The complexity of the structural organisation of animals increases as we move from unicellular to multicellular organisms. In unicellular organisms, a single cell carries out all the physiological functions performed by a living organism such as digestion, respiration, reproduction, excretion, etc.
Let’s learn about the types of animal tissues and some interesting facts about them.
Facts About Animal Tissues and Types
Animal tissues are categorised into four main types, namely, Epithelial tissue, Connective tissue, Muscular tissue and Nervous tissue.
Epithelial tissue provides a covering to almost everything in our body and provides protection. It covers the body surface, organs and cavities. It acts as a barrier between different structures of the body.
Simple epithelium is made up of a single layer of cells and is present as the lining of body cavities and ducts. The compound epithelium is made up of multiple layers of cells and acts as a protective covering, e.g. skin.
Epithelial tissue is further categorised into three types according to cell structure, they are:
- Squamous epithelium – form the diffusion boundary of blood vessels and alveoli in the lungs.
- Cuboidal epithelium – main functions are secretion and absorption, present in glandular ducts and tubules of kidneys.
- Columnar epithelium – line the stomach and intestine and perform secretion and absorption. The nucleus is present at the base of slender cells.
Ciliated epithelium cells bear cilia on their free surface and are part of respiratory and reproductive tracts.
The glandular epithelium is cuboidal or columnar cells specialised for secretion. Goblet cells are unicellular and salivary glands are multicellular.
Connective tissue provides support and transport substances. Examples of connective tissue are blood, bone, cartilage and adipose tissue.
Blood is a fluid connective tissue. It is made up of plasma, red blood cells, white blood cells and platelets. An interesting fact about our mature red blood cells is that they are devoid of a nucleus.
Cells of connective tissues with the exception of blood secrete fibres of collagen or elastin proteins, which are responsible for strength and flexibility.
Adipose tissue is a type of loose connective tissue. It stores fat.
Tendons and ligaments, which join bones to muscle and two bones together, respectively, are types of dense connective tissue.
Cells of cartilage tissue are known as chondrocytes and of the bones are known as osteocytes.
Muscle tissue is made up of many long fibres arranged in a parallel fashion and are responsible for all the voluntary and involuntary movements in the body.
Muscle tissue is of three types:
- Skeletal muscle – They are associated with the skeletal system or bones. They are striated in appearance and responsible for locomotion and voluntary movements.
- Smooth muscle – They are nonstriated and present in the walls of blood vessels, reproductive and digestive tracts. They are under involuntary control of the nervous system.
- Cardiac muscle – Present in the heart. They are striated in appearance and are involuntary.
Neural tissue is responsible for communication, control and regulation. It constitutes brain, spinal cord and peripheral nerves. Neurons are the basic unit of the nervous system. Glial cells are the support cells of nervous tissue.
The main parts of a neuron are:
- Dendrites – They are the short branched projections from the cell body. They conduct nerve impulses to the cell body.
- Cell body – It contains a nucleus, cytoplasm with cell organelles and Nissl’s granules.
- Axon – It is a long fibre, which transmits nerve impulses to a synaptic or neuromuscular junction, from the cell body. Each branch of an axon terminates in a synaptic knob, which contains neurotransmitters.
This was in brief about different types of animal tissues. For more information related to the structural organisation in animals, subscribe to BYJU’S YouTube Channel for more information.