What is Tissue?

Tissues are like the fabric of our body. The term means “woven.” When two or more tissues combine, they form our organs. Our kidneys, lungs, liver, and other organs are all made of different types of tissues. But what function a certain part of our organ performs, depends on what kind of tissue it’s made of. This is the tissue that lines, covers, and generally organizes our body, creating order during the disturbance in the body.

Definition of Tissue

Tissues are the groups of similar cells that work together to perform their defined function and in doing so they form tissues which essentially are the fabric of our body which holds us together and gives shape to our organs.

What are Tissues?

Tissues are clusters of cells that perform the same purpose as cells. The study of human and animal tissues is known as Histology. Xavier Bichat coined the term “tissue” in 1801. They can also be considered the building blocks of an organ. Tissue contributes to the formation of organs in a body. Each tissue carries out a specific function, such organisms with many tissues are called multicellular organisms. Multicellular organisms have tissues in their bodies which are placed at specific places to carry out specific functions, this is called division of labor in the organism’s body.

Each tissue has two components- cells and matrix. A cluster of cells make tissue and a matrix is a substance found between the cell. It is also called an extracellular substance. Tissues are regarded as the most important component of human anatomy. Tissues in multicellular organisms are loosely classified into four basic types epithelial, connective, muscle and nervous tissue.

Types of Animal Tissues

Animals require tissues for more than just physical reasons since they travel from place to place. Almost all tissues in animals are living tissues. These tissues require nutrition, which they obtain from the organism’s body. Because animals have homogeneous growth throughout their bodies, tissues split and disseminate throughout their body parts. Blood is a connective tissue in the human body that helps carry nutrients, hormones, and waste products.

Four primary types of animal tissue are:

1. Epithelial Tissue
2. Connective Tissue
3. Muscular Tissue
4. Nervous Tissue

1. Epithelial Tissues

These tissue cells produce a sheet-like structure that either covers the exterior surface or lines the internal processes. These tissues are classified as:

• Simple: One layer, thick, like the epidermis of skin
• Stratified: Two or more layers, like the lining of the oesophagus
• Ciliated: Like lung alveoli
• Pseudostratified: Only a single layer of cells, but it appears to have multiple layers because the cell nuclei lie at different levels and not all cells reach the apical surface.

Simple and stratified epithelial tissues are also categorised into the following kinds based on shape:

• Squamous: These are thin plate-like cells arrayed like tiles on the floor, such as the lining of the mouth, nose, blood vessels, and so on.
• Cuboidal: These cells have a cube shape, such as kidney tubules or thyroid vesicles.
• Columnar: These are cylindrical in shape, such as the lining of the intestine.
• Transitional: These cells alter shape as organs, such as the urinary bladder, stretch and relax.

2. Connective Tissues

Connective tissues unite and connect parts of the body and organs. It is made up of three components:

• Cells
• Fibres
• Matrix (ground substance)

The following are the numerous forms of connective tissue:

1. Areolar Connective Tissue: These are composed of yellow and white fibres and cells. They serve as supporting and packing material, a passage for blood vessels, and a means of attaching the skin to the muscles.
2. Adipose Connective Tissue: It is made up of fat cells. It offers insulation, stores body reserves, and acts as a shock absorber.
3. Reticular Connective Tissue: Made up of branched fibres. Forms the foundation for a variety of vital organs such as the liver, spleen, tonsils. Bone and cartilage are supportive connective tissues, whereas blood is a fluid connective tissue.

Bone (Osseous Tissue)

It is a type of connective tissue that is both strong and flexible. It is composed of three primary connective tissue components.

1. Solid Matrix: A protein matrix coated with calcium and magnesium salts such as phosphates and carbonates.
2. Cells: Bone cells are known as oesteoblasts and osteocytes. These cells are found in fluid-filled areas known as lacunae.
3. Fibres: These are collagen fibres.

Cartilage

It is a flexible but less vascularised connective tissue than bone. Its structure is similar to bone, with a protein matrix and cells suspended in the matrix known as chondrocytes. Cartilage cells are found in groups of two or three in lacunae. It is found in flexible regions such as the ear pinna, epiglottis, trachea rings.

3. Muscular Tissue

These are of 3 types:

1. Skeletal or Striated Muscle Fibres: Alternate light and dark bands aer present in these fibres. The fibres are cylindrical, multinucleate with peripheral nuclei. They are voluntary and attached to the skeleton.
2. Smooth Muscle Fibres: There fibres have no stripes. These are spindle-shaped, pointed at both the ends, bear a single nucleus which is central. They are involuntary and present in internal organs.
3. Cardiac Muscle Fibres: These are striped muscular fibres as well. There form branch like structure. The existence of “tight junctions” suggests that these are multinucleate with central nuclei. They are found in the heart and are involuntary. Their primary purpose is to contract the heart.

4. Nervous Tissues (Neuron)

Nervous tissue is made up of three main components:

1. Cell body: With a nucleus as well as strongly pigmented particles known as Nissl granules (ribosomes) and other cellular organelles.
2. Dendrite: Many short processes known as dendrites accept information or impulses.
3. An Axon: A single, long process with fine branching at the ends. Axons of myelinated nerve fibres are lined by a lipid layer called the myelein sheath, which is interrupted at certain sites called Nodes of Ranvier.

Functions of Animal Tissues

The following are the functions of animal tissues:

• Animal tissues functions include protection, transport secretion, sensory reception.
• Provide the Maintenance of posture, Generation of heat (thermogenesis) etc.
• Provide movement of the internal organs.

Types of Plant Tissues

Plants do not have the same tissues as humans, and their movement is limited. Plants require dead tissues for mechanical support, hence they do not require living tissues. Plants have two types of tissues: those that divide and those that do not divide. Plants do not grow uniformly throughout their bodies; instead, growth is restricted to some areas, which contain tissues that can divide. Plant tissues can be divided into plant tissue systems, each of which performs a specific purpose.

A plant tissue system is a functional unit that connects all of a plant’s organs. The plant tissue system is also divided into different tissues based on their functions. Plant tissues are divided into Meristematic tissue and Permanent tissues based on their ability to divide.

Meristematic Tissue

Made up of a group of cells with the ability to divide. They are small, cuboidal, densely packed cells that divide to generate new ones. These tissues can stretch, enlarge, and differentiate into other types of tissues. Meristematic tissues are classified into three groups based on their location:

• Apical meristems
• Lateral meristems
• Intercalary meristems

Permanent Tissue

These tissues have lost their ability to divide and are produced from meristematic tissues. They have reached their mature state. They are further classified into two types:

• Simple
• complex

Simple Permanent Tissue

These are made from Parenchyma, Collenchyma and Sclerechyma.

Parenchyma

Found in the soft sections of plants such as roots, stems, leaves, and flowers. Tissue cells are loosely packed and have wide intercellular spaces between them. A vacuole is located in the centre of each cell. Storage, photosynthesis, and helping the plant float on water are all activities of parenchyma tissues.

Collenchyma

Cells have stronger cell walls than parenchyma cells. They are intended to offer mechanical support to the plant structure in areas such as the leaf’s petiole.

Sclerechyma

This tissue’s cells are dead. They are stiff and have thick, lignified secondary walls. Their primary role is to offer strength and support to plant sections.

Complex Permanent Tissue

Made up of several types of cells, as opposed to simple permanent cells. Plant vascular bundles contain complicated permanent tissues called xylem and phloem. Xylem was created by tracheids, vessels, xylem parenchyma, and xylem fibres. Tracheids and vessels are hollow tube-like structures that let water and minerals move.

Functions of Plant Tissues

The following are the functions of plant tissues:

• Provide photosynthesis, storage and secretion.
• Provide mechanical support to the growing parts of the plant.
• Help in the mechanical strength of organs, flexibility of the organs.
• The xylem and phloem tissues help in material transfer throughout the plant.
• They divide to make new cells and aid in plant growth.
• They aid in cellular metabolisms such as photosynthesis, regeneration, and respiration.

FAQs on Tissue

1. What are Tissues?

A group of cells that have similar structure and function together as one unit is known as tissue. There are 4 basic types of tissue: connective tissue, epithelial tissue, muscle tissue, and nervous tissue. Connective tissue supports other tissues and binds them together (bone, blood, and lymph tissues.

2. What is the function of Tissue?

A group of cells that have similar structure and function together as one unit is known as tissue. Tissues provide shape to the body and help body to conserve heat and store energy. There are four types of tissues: Connective tissue, Epithelial tissue, Muscle tissue and Nervous tissue.

3. What is Permanent Tissue?

Permanent tissues are a group of living or dead cells which are formed by meristematic tissues that have lost their ability to divide. That is, these tissues have undergone differentiation and are incapable of meristematic activities.

4. What is Human Tissue?

Human body tissue makes up organs and other body parts. There are four types of tissue: muscle, epithelial, connective and nervous. All tissues are made up of specialized cells that are grouped together according to structure and function. Muscle is found throughout the body and even includes organs such as the heart.

5. Who Discovered Tissue?

The concept of tissues can be traced back to 1801 when it was introduced by Xavier Bichat, a French anatomist and pathologist. He had proposed that tissues are a central element in human anatomy, concluding that organs are essentially a collection of distinct tissues.