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By the end of this section, you will be able to:
  • Identify the four main tissue types
  • Discuss the functions of each tissue type
  • Relate the structure of each tissue type to their function
  • Discuss the embryonic origin of tissue
  • Identify the three major germ layers
  • Identify the main types of tissue membranes

The term tissue    is used to describe a group of cells found together in the body. These cells work together to perform a certain function. The cells might protect us, fight disease or produce hormones.

Although there are many types of cells in the human body, they are organized into four broad categories of tissues: epithelial, connective, muscle, and nervous . Each of these categories is characterized by specific functions that contribute to the overall health and maintenance of the body. Histology is the microscopic study of tissue appearance, organization, and function.

The four types of tissues

Epithelial tissue , also referred to as epithelium, refers to the sheets of cells that cover exterior surfaces of the body, line internal cavities and passageways, and form certain glands. Connective tissue , as its name implies, binds the cells and organs of the body together and functions in the protection, support, and integration of all parts of the body. Muscle tissue is excitable, responding to stimulation and contracting to provide movement. Nervous tissue is also excitable, allowing the formation of signals that communicate between different regions of the body ( [link] ).

The next level of organization is the organ, where several types of tissues come together to form a working unit. Just as knowing the structure and function of cells helps you in your study of tissues, knowledge of tissues will help you understand how organs function. The epithelial and connective tissues are discussed in detail in this chapter. Muscle and nervous tissues will be discussed only briefly in this chapter.

Four types of tissue: body

This diagram shows the silhouette of a female surrounded by four micrographs of tissue. Each micrograph has arrows pointing to the organs where that tissue is found. The upper left micrograph shows nervous tissue that is whitish with several large, purple, irregularly-shaped neurons embedded throughout. Nervous tissue is found in the brain, spinal cord and nerves. The upper right micrograph shows muscle tissue that is red with elongated cells and prominent, purple nuclei. Cardiac muscle is found in the heart. Smooth muscle is found in muscular internal organs, such as the stomach. Skeletal muscle is found in parts that are moved voluntarily, such as the arms. The lower left micrograph shows epithelial tissue. This tissue is purple with many round, purple cells with dark purple nuclei. Epithelial tissue is found in the lining of GI tract organs and other hollow organs such as the small intestine. Epithelial tissue also composes the outer layer of the skin, known as the epidermis. Finally, the lower right micrograph shows connective tissue, which is composed of very loosely packed purple cells and fibers. There are large open spaces between clumps of cells and fibers. Connective tissue is found in the leg within fat and other soft padding tissue as well as bones and tendons.
The four types of tissues are exemplified in nervous tissue, stratified squamous epithelial tissue, cardiac muscle tissue, and connective tissue in small intestine. Clockwise from nervous tissue, LM × 872, LM × 282, LM × 460, LM × 800. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)

Tissue membranes

A tissue membrane    is a thin layer or sheet of cells that covers the outside of the body (for example, skin), the organs (for example, pericardium), internal passageways that lead to the exterior of the body (for example,inside of cheek), and the lining of the moveable joint cavities. A synovial membrane    is a type of connective tissue membrane that lines the cavity of a joint. For example, synovial membranes surround the joints of the shoulder, elbow, and knee which form synovial fluid, a natural lubricant for the joints.

Tissue membranes

This illustrations shows the silhouette of a human female from an anterior view. Several organs are showing in her neck, thorax, abdomen left arm and right leg. Text boxes point out and describe the mucous membranes in several different organs. The topmost box points to the mouth and trachea. It states that mucous membranes line the digestive, respiratory, urinary and reproductive tracts. They are coated with the secretions of mucous glands. The second box points to the outside edge of the lungs as well as the large intestine and states that serous membranes line body cavities that are closed to the exterior of the body, including the peritoneal, pleural and pericardial cavities. The third box points to the skin of the hand. It states that cutaneous membrane, also known as the skin, covers the body surface. The fourth box points to the right knee. It states that synovial membranes line joint cavities and produce the fluid within the joint.
The two broad categories of tissue membranes in the body are (1) connective tissue membranes, which include synovial membranes, and (2) epithelial membranes, which include mucous membranes, serous membranes, and the cutaneous membrane, in other words, the skin.

The Cutaneous membrane is composed of epithelium attached to a layer of connective tissue, and is the membrane you know as your skin. The mucous membrane    is also made of of connective and epithelial tissues. These membranes line the body cavities and hollow passageways that open to the external environment , and include parts of the digestive, respiratory, excretory, and reproductive tracts. Mucous, produced by glands called goblet cells , covers the membrane.

A serous membrane    is an epithelial membrane that lines the closed cavities of the body, that is, those cavities that do not open to the outside. They also cover the organs located within those cavities. Three serous membranes line the thoracic cavity; the two pleura that cover the lungs and the pericardium that covers the heart. A fourth, the peritoneum, is the serous membrane in the abdominal cavity that covers abdominal organs and forms double sheets of mesenteries that suspend many of the digestive organs.

Chapter review

The human body contains more than 200 types of cells that can all be classified into four types of tissues: epithelial, connective, muscle, and nervous. Epithelial tissues act as coverings controlling the movement of materials across the surface. Connective tissue integrates the various parts of the body and provides support and protection to organs. Muscle tissue allows the body to move. Nervous tissues send information from one part of the body to another.

Different types of tissues form membranes that enclose organs, provide a friction-free interaction between organs, and keep organs together. Synovial membranes are connective tissue membranes that protect and line the joints. Epithelial membranes are formed from epithelial tissue attached to a layer of connective tissue. There are three types of epithelial membranes: mucous, which contain glands; serous, which secrete fluid; and cutaneous which makes up the skin.

Questions & Answers

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Source:  OpenStax, Histology. OpenStax CNX. Feb 27, 2015 Download for free at http://legacy.cnx.org/content/col11764/1.1
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