When the smallest unit of life i.e. cells are grouped together they form tissues. These groups are cells that are functionally and structurally similar and unite to perform specialized functions.
Tissues are present in multicellular organisms, but not in unicellular, and even simple species of multicellular species like sponges, tissues are not well developed. But at a higher level of multicellularity like plants and animals, tissues are highly differentiated and specialized in their functions and can work according to the environment in an organized manner.
In the study of evolution, it was found that tissues got united to form the organs, which further became segregated and developed into specialized parts. Earlier, embryologist classified the tissues on the ground of their series of origin in the developing embryo, those were ectodermal, mesodermal and endodermal tissues.
However, the most useful and acceptable system to classify the animal tissues on the basis of their functions they perform, and in this way they are been divided into four categories, which are: epithelial tissues; nervous tissues; muscle tissues and connective tissue.
Such kind of tissues, that serves in animal’s growth and repair, with also performing in storage, transportation of energy and accumulation of nutrients and excretion of waste products. These tissues are present in maximum parts of the human body, i.e. in the digestive tract that includes the mouth to pharynx, stomach, intestines and anus, it is also found in liver, lungs, urinary tract, heart chambers and kidneys. They are also found on the surface of exposed skin.
Epithelial tissues are made up of epithelial cells, these cells are tightly packed, having no inter-cellular space. These tissues are responsible for the secretion of hormones, mucus, enzymes, etc. and then carrying it to to the circulatory system.
Functions of epithelial tissues
- It plays a major role in protecting the body’s organs, and also provide mechanical strength to the underlying cells.
- It secrets gastric juices in the stomach, and play critical roles in excretion, filtration, and other metabolic activities.
- It removes waste from the skin through sweat and protects from radiations.
- Absorbs digested food in the intestine and also fights against the pathogens, toxins, etc.
Types: Simple, columnar, stratified, squamous, cuboidal, pseudostratified, specialized.
The second kind of tissues is well known for their coordination and work via electrical impulses (that runs through the nerve fibres) and chemically by releasing hormones into the bloodstream. These type of tissues are found in the nervous system and are composed of highly specialized cells.
The critical function is in the transmission of signals, here the nervous system transmits signals to the brain and spinal cord. The special cells ‘neurons’ conduct these impulses and respond accordingly by the use of our senses.
Functions of the nervous tissues
- It responds or reacts to various physical and chemical signals – Irritability.
- It has the ability to transmit the resulting reaction on the signals given – Conductivity.
- It also transmits the signals to all the parts of the body.
- It regulates the various emotions of the human body and strengthening mental awareness.
- It quickly responds as per the change in the surroundings.
- It also regulates the metabolic activities.
Such types of tissues that are composed of muscles cells (fibres) are known as muscles or muscular tissues. These muscles tissues rhythmically contract and relaxes. These tissues are extensible, elastic and contractile.
Muscles tissues are mainly responsible for producing force and motions, these motions can be within the body or locomotion. There are three types of muscular tissues: skeletal muscles, cardiac muscles and smooth or visceral muscles.
Skeletal muscles are such types of muscles that are connected to bones, while cardiac muscles are the involuntary muscles, that are found in the heart, thirdly smooth muscles are present in the inner linings of the various organs.
Functions of the muscles tissues
- It is responsible for the voluntary and involuntary movements.
- Helps to maintains the erect posture of the body.
- Regulate the pumping of blood and its flow from arteries and veins.
- It also regulates the pumping of the air, in and out of the body.
Types: Cardiac, striated, non-striated, smooth, skeletal.
Connective tissues are known for the movements and support provided to the body, as these tissues surround the organs, muscles, and bones and hold them together. Tendons, ligaments, cartilage, and bones are the type of strong connective tissues. These tissues are composed of elastic, collagen, reticular fibres, and other ground substances.
The connective tissues are abundantly present in our body. Connective tissues have a large amount of intercellular substance (matrix) as the cells are separated from each other, as well as extracellular matrix (non-living material). This type of tissues is made from various cells like leukocytes, macrophages, fibroblast, fat cells and mast cells.
Bones, blood, tendons, ligaments, alveolar tissues are some of the examples of the connective tissues.
Functions of the connective tissues
- Connective tissues are known for providing support to the body.
- It acts as an insulating, by maintaining the body’s temperature.
- These tissues also store energy and also protect the body from various external shocks.
- Mainly it also transports the materials to and from various parts of the body.
- Fighting against foreign particles or pathogens.
- It also provides shape to the body and helps in the transportation of hormones, nutrients, enzymes, gases, minerals, and other substances within the body.
Types: Reticular, elastic, and collagen.