Four Types of Tissue
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. A disruption of the structure is a sign of injury or disease. Such changes can be detected through histology, the microscopic study of tissue appearance, organization, and function.
- Tissues are a group of similar cells that carry out a specialized function.
- There are four broad classifications of tissue: epithelial, connection, muscle, and nervous tissue.
- Each tissue type also has sub-classifications.
What are Tissues?
Tissues are groups of similar cells group of similar cells carrying out related functions. These tissues combine to form organs—like the skin or kidney—that have specialized functions within the body. Organs are organized into organ systems to perform functions. For example, the circulatory system consists of the heart and blood vessels, while the digestive system, consists of several organs, like the stomach, intestines, liver, and pancreas. Collectively, organ systems work together to for a organism for function properly.
Although there are many types of cells in the human body, they are organized into four broad categories of tissues:
- Epithelial Tissue
- Connective Tissue
- Muscle Tissue
- Nervous Tissue
Epithelial tissues provide the body’s first line of protection from physical, chemical, and biological wear and tear. The cells of an epithelium act as gatekeepers of the body controlling permeability and allowing selective transfer of materials across a physical barrier. All substances that enter the body must cross an epithelium. Some epithelia often include structural features that allow the selective transport of molecules and ions across their cell membranes.
Many epithelial cells are capable of secretion. Some epithelial cells secrete mucous. One example being the cells of the respiratory tract that secrete mucous to trap incoming microorganisms and particles. Other epithelial cells can secrete enzymes. For example, the epithelial cells of the small intestine releases digestive enzymes.
There are three general classifications whose names a derived by their appearance: sqaumous, cubodial, and columnar. Squamous cells appear to be like ‘scales’; cubodial cells appear to be cube-shaped; and columnar cells like columns. Note that there are also subclassifications of these, and also a couple other general classifications.
Connective tissue is diverse collection of tissues that support and connect other tissues, but also have protective functions. A main feature of connective tissue is that they contain a matrix that gives the tissue it’s density.
Some bones – like our rib cage – protect delicate organs and. Specialized cells in connective tissue defend the body from microorganisms that enter the body. Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and lymph. Adipose cells store surplus energy in the form of fat and contribute to the thermal insulation of the body.
The primary function of muscle tissue is movement, but muscle has an important role in generating heat for the body. Muscle cells are excitable, meaning they generate a current when stimulated. When muscle cells are excited, they tend to contract – or shorten. If muscle tissue is attach to two different bones, when that muscle shortens, one of the bones will be pulled.
Some muscle movement is voluntary, which means it is under conscious control. Most voluntary movement is the work of skeletal muscle. Other movements are involuntary. The contraction of your pupil and the movement of digested food through your intestines is the work of smooth muscle. While the contractions of our heart is also involuntary, it is done by a separate class of muscle tissue called cardiac muscle.
Nervous tissue is characterized as being excitable and capable of sending and receiving electrochemical signals that provide the body with information. Two main classes of cells make up nervous tissue: the neuron and neuroglia. Neurons propagate information via electrochemical impulses, called action potentials, which are biochemically linked to the release of chemical signals. Neuroglia play an essential role in supporting neurons and modulating their information propagation.
- Clark MA, Douglas M, Choi J. “33.2 Animal Primary Tissues.” Biology 2e. OpenStax, 2018. Houston, TX. https://openstax.org/books/biology-2e/pages/33-2-animal-primary-tissues. License: CC BY 4.0 | License Terms: Edited & Adapted | Access for free https://openstax.org/books/biology-2e/pages/1-introduction.
- Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, Korol O, Johnson JE, Womble M, DeSaix P. “4.1 Types of Tissues.” Anatomy and Physiology. OpenStax, 2013. Houston, TX. https://openstax.org/books/anatomy-and-physiology/pages/4-1-types-of-tissues. License Terms: Edited & Adapted | Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.