Content area
Full Text
Abstract
This article, which forms part of the life sciences series, examines cellular organisation in the formation of body tissues, membranes, organs and systems. Four main types of body tissue are described: epithelial, connective, muscle and nervous tissue. Each class of tissue is described in terms of its structure and function. Where appropriate, subgroups within the classifications are identified. Different membranes in the body are considered and the organisation of tissues and membranes into more complex structures, such as organs and body systems, is outlined.
Keywords
Body systems, cells, membranes, organs, tissues
Early in emb ryonic life, cells begin to differentiate according to the functions they will later assume in life. Various types of cells are organised into structures of increasing complexity. In this article, levels of cellular organisation are discussed. Tissues, which are collections of cells that have a common origin, are considered. A number of different types of tissue exist in the body. The article provides a brief overview of the arrangement of cells to form sheets of material or membranes. The organisation of tissues and membranes into more complex structures such as organs and body systems is also outlined.
Tissues
Tissues of the body consist of many cells, which are not identical, but have the same origin, acting together to perform a common function. Tissues vary in terms of the size, shape and function of the cells (Thibodeau and Patton 2010). Organs are formed by the functional grouping of two or more tissues serving a common purpose. In the body, organs and tissues are organised into systems that carry out specific aspects of human physiology, for example respiration. These are known as body systems. The different body systems are listed in Box 1.
There are four main types of tissue, based on their structure and functions, including epithelial, connective, muscle and nervous tissue.
Epithelial tissue
Epithelial tissue (epithelium) can be divided into two types:
* Covering and lining epithelium.
* Glandular epithelium.
Epithelium covers the internal and external organs of the body and lines vessels, body cavities, glands and organs. Glandular epithelium is composed of secreting cells and is found in sweat or salivary glands.
Epithelial cells are packed closely together with little extracellular material between them. They are arranged in...