What is Tissue?

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Introduction

In biology, the tissue is defined as a cellular organizational level between cells and a complete organ. A tissue is an ensemble of likewise cells and their extracellular matrix from the same origin that carries out a specific function together. Then the organs are formed by the functional grouping of multiple tissues together.

The word "tissue" has derived from the French word "tissu", which means that, something that can be "woven", from the verb tisser, which means "to weave".

The study of both animal and human tissues is called histology or, in connection with disease, as histopathology. For plants, the discipline is referred to as anatomy. The classical tools for studying tissues are paraffin blocks, where the tissue is embedded first, and then sectioned the histological stain and, finally, the optical microscope. Developments in electron microscopy, the use of frozen tissue sections, and immunofluorescence have enhanced the detail that can be observed in tissues. The classical appearances of tissues with these tools can be examined in health and disease, enabling considerable refinement of prognosis and medical diagnosis.

Types of Tissues

Tissues are available in both plants and animals, where the brief description is given below.

Animal Tissues

These tissues are grouped into four basic types, as given below.

  1. Connective

  2. Muscle

  3. Nervous, and

  4. Epithelial


Collections of these tissues joined in units to serve a common function composed of organs. While all animals, in general, can be considered to contain the four tissue types, the manifestation can differ based on the organism type. For instance, the origin of the cells comprising a specific tissue type may developmentally differ for various classifications of animals.

  1. Connective Tissue

Connective tissues are the fibrous ones made of cells separated by non-living material, which is known as an extracellular matrix. This matrix can be either liquid or rigid. For example, blood comprises of plasma as its matrix and bone matrix are rigid. Connective tissue provides shape to organs and holds them in place. Bone, blood, tendon, ligament, areolar, and adipose tissues are connective tissue's examples. A method of classifying the connective tissue is to divide them into three types: skeletal connective tissue, fluid connective tissue, and fibrous connective tissue.

  1. Muscular Tissue

Muscle cells form the active body contractile tissue are called muscle or muscular tissue - these functions to create force and cause motion, either movement or locomotion within the internal organs. The muscle tissue is separated into three distinct categories: smooth or visceral muscle, which is found in the organ's inner linings; skeletal muscle, attached to the bones typically, which generate gross movement; and cardiac muscle, found in the heart, contracts to pump blood throughout an organism.

  1. Nervous Tissue

Cells comprising the peripheral nervous system and central nervous system are classified as nervous (or neural) tissue. Neural tissue forms both the brain and spinal cord in the central nervous system. In a peripheral nervous system, the neural tissues form the spinal and cranial nerves, inclusive of the motor neurons.

  1. Epithelial Tissue

These tissues are formed by the cells that cover the organ surfaces, like the surface of the skin, surfaces of soft organs, the reproductive tract, the inner lining, and the airways of the digestive tract. The cells that comprise an epithelial layer are linked through tight junctions, semi-permeable; thus, this tissue provides a barrier to the external environment and the organ it covers. Besides the protective function, epithelial tissue can also be specialized to function in excretion, absorption, and secretion. Epithelial tissue helps to protect organs from injury, fluid loss, and microorganisms.

Plant Tissue

Plants have their own set of tissues, which are known as a dermal, ground, and vascular tissues.

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  1. Dermal Tissue

Dermal tissue covers the outside part of a plant in a single layer of cells called the epidermis. We can think of epidermis as the plant's skin. It mediates many interactions between a plant and its environment. Epidermal cells secrete cuticle, a waxy substance, which waterproofs, coats, and protects the above-ground parts of the plants. Cuticles help to prevent water loss, infections, abrasions, and damage from toxins.

  1. Ground Tissue

The ground tissues make up many of the interiors of a plant and carry out the basic metabolic functions. Ground tissue present in stems provide support and can store water or food. Ground tissues may also store food in roots.

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  1. Vascular Tissue

Vascular tissue runs within the ground tissue inside a plant. Our body was able to grow from a single cell to perhaps 100 trillion cells because, after 21 days of fertilization, a tiny heart began to pump blood throughout our tiny self - and it hasn't stopped since. The blood that it pumps to carry water, nutrients, and oxygen to each one of our trillions of cells, and removes carbon dioxide and other wastes. Although plants don't have hearts, they do have vessels that transport minerals, water, and nutrients through the plant. These are the vascular tissue vessels and consist of phloem and xylem. Phloem and xylem are packaged together in bundles, as shown in the figure below.

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FAQ (Frequently Asked Questions)

1. Explain the Functions of Epithelial Tissues.

The functions of epithelial tissues can be listed below.

  • The principle functions of epithelial tissue include covering and lining of free surface

  • Inside the body, the epithelial cells form the lining of the alimentary canal and mouth and protect these organs

  • The body surface cells form the outer layer of skin

  • Epithelial tissues help in the waste elimination

  • They help in the absorption of nutrients and water 

  • A few epithelial tissues perform secretory functions. They also secrete a variety of substances including saliva, sweat, mucus, enzymes, and more

  • Epithelial tissues secrete hormones and/or enzymes in the form of glands

2. Give a Summary of Plant Tissues.

A brief summary of plant tissue can be listed below.

  • Three plant cell types are found in each of the major plant tissues: ground, dermal, and vascular tissues

  • The ground tissues make up most of the interior parts of a plant. It carries out the basic metabolic functions and stores water and food

  • Dermal tissue covers the outside parts of a plant in a single layer of cells known as the epidermis. It also mediates the majority of the interactions between a plant and its environment

  • Vascular tissue runs through the ground tissue that is present inside a plant. It consists of bundles of phloem and xylem, which transport water, food, and minerals throughout the plant