Tissue

Tissue is the name for a group of similar cells that have a common structure and function and which work together. Tissues fit together to form organs in higher animals These animals have four basic types of tissue.

The animal body is made up of many different kinds of cells. These specialize to perform certain functions, or specific tasks. A group of closely associated or similar cells that work together to do one thing is called a tissue. All the cells in a tissue look very similar and all do the same work.

TYPES OF TISSUE

There are four types of animal tissue: epithelial, connective, muscle, and nervous tissue. Every cell in each of these tissues is an independent unit, yet all of the cells in a given tissue interact with one another. They must do this in order to perform a certain necessary function for the animal's body. For example, an animal's brain is made of nerve tissue that is composed of millions of connected nerve cells. In animals, when two or more tissues are associated and work together, they form an organ such as the stomach or the heart.

The same is true for plants, except they have only three types of tissue. Plant tissue, like animal tissue, is also organized into organs, so that epidermal plant tissue makes up the organ known as a leaf. For both plants and animals, a tissue is the "stuff," or specific type of cellular material, out of which specialized organs are made.

HUMAN TISSUE

As animals, humans have four different types of tissues: epithelial, connective, muscle, and nervous tissue.

Epithelial Tissue. The epithelial tissue, whose closely packed cells make it ideal for forming a lining or a covering, is what makes up the skin. This tissue also makes up the lining for the organs and the many passageways. Because its cells are so tightly packed together, it allows the skin to be an excellent barrier and protects the body against injury and invading microorganisms (any form of life that is too small to be seen without a microscope). It also regulates fluid loss.

Nervous Tissue. The nervous tissue is made up of cells called neurons. These are designed to carry impulses. This highly specialized tissue carries electrical signals from one part of the body to another and allows it to function as an organized unit.

Muscle Tissue. Muscle tissue is responsible for producing movement. Its cells are designed to work by contracting and relaxing. They also are built to respond to stimuli transmitted by neurons. There are three types of muscle tissue. Smooth muscle makes up organs that people do not control, such as the intestines. Striated, or skeletal muscle, is under people's control and makes up the muscles that allow people to move. Cardiac muscle is also called heart muscle and is responsible for the regular and powerful contraction of the heart. Unlike skeletal muscle, it never needs to rest.

Connective Tissue. Finally, connective tissue is the most common tissue in the body, and it is what holds the entire body together. Bone, cartilage, and blood are made of connective tissue. Bone is a type of mineralized connective tissue, cartilage is found between joints, and blood is considered to be a connective tissue in liquid form since it circulates throughout the body.

PLANT TISSUE

Plants have three types of tissue. Their epidermal tissue serves a purpose similar to humans, in that it covers the surfaces of leaves, stems, and roots and protects its inner parts. The tissue through which a plant transports materials is called its vascular tissue. Its cells are elongated and form tubelike organs. The rest of a plant is made up of what is called fundamental plant tissue. In plants and animals then, tissues are the intermediary stage between an organism's individual cells and its specialized organs. Therefore, cells are arranged into groups, called tissues, and tissues are eventually grouped into organs.

[See alsoCell; Organ ]