We have an Array of animals on our planet ranging from unicellular to multicellular. In unicellular organisms, a single cell carries out all the body functions such as digestion, respiration, and reproduction. Different cells, however, carry out various activities in multicellular organisms. A tissue is a collection of related cells that carry out a certain job. Interestingly all complex animals including human beings have only four basic types of tissues. To create organs like the kidney, stomach, and heart, these tissues are arranged in a particular ratio and arrangement. Sometimes two or more organs interact physically or chemically to perform a common function. Such organs together form an organ system such as the digestive or respiratory systems. Animal tissues can be broadly divided into four kinds according to how they function: epithelial, connective, muscular, and neural tissues.
Epithelial Tissue- Epithelial tissue is commonly known as epithelium, these cells have a free surface, which either faces the body fluid or the outer environment. Thus the epithelium serves as a lining or a protective covering for body parts. Epithelial cells are tightly packed together and have minimal intercellular matrix. Specialized junctions found in the epithelium and other tissues act as linkages between cells on a structural and functional level. There are three different sorts of junctions: tight, adherent, and gap. Tight Junctions prevent the leakage of substances across a tissue. Simple and compound epithelial tissues are the two types. Simple epithelium lines bodily cavities, ducts, and tubes and is made up of just one layer of cells. Two or more layers of cells make up the compound epithelium. Its main job is to defend against chemical and mechanical stress.
Connective Tissues- Connective tissues are the most abundant and widely distributed tissues in animals. As the name suggests, these tissues help link and support other tissues and organs throughout the body. These tissues range from soft to specialized tissues such as cartilage, bone, adipose, and blood. Except for blood, the cells of connective tissue secrete collagen fibers, which are made of protein. These fibers provide strength, elasticity, and flexibility to the tissue. The connective tissue cells also secrete modified polysaccharides, which accumulate in the cell and fibers and serve as a matrix or ground substance. Connective tissues are categorized into three types: Loose Connective, Dense Connective & Specialized Connective.
Muscle Tissue- The body’s muscle tissues enable movement, blood pumping, and passage of food through the digestive tract. Proteins called actin and myosin enable the contraction of muscle cells. There are three types of muscles visible: Skeletal Muscle, Cardiac Muscle, and Smooth Muscle.
Nervous Tissue- Information is processed and sent by this sort of tissue, which is made up of neurons and neuroglial cells. Neurons produce electrical signals known as nerve impulses that enable them to quickly transmit information over great distances. The neural functions are supported by neuroglia.
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