Tissues and body cavities

Chapter 2 Tissues and body cavities

Within the body individual cells are grouped together to form tissues and organs. Thus:

Body tissues

Each tissue type consists of three main components:

There are four main types of tissue:

Epithelial tissue

Epithelial tissue or epithelium covers the surface of the body and the organs, cavities and tubes within it – it covers the internal and external surfaces of the body. Its main function is to protect delicate structures lying beneath it but in some areas the epithelium may be secretory, e.g. glands, or absorbent, e.g. in the small intestine. The epithelium lining structures such as the inside of the heart, blood vessels and lymph vessels is referred to as endothelium.

Epithelium may be described according to the number of layers of cells, i.e. its thickness:

The thickness of the epithelium reflects its ability to protect: the more layers of cells, the more protection is provided. The epithelium on the footpads consists of many layers of cells providing protection when walking on rough surfaces, while the epithelium over the abdominal wall is only a few cells thick and additional protection is provided by fur. Further protection may be provided by the presence of the protein keratin. The epithelium is described as being a keratinised stratified epithelium and this type can be seen in claws and nails.

Epithelium may also be described according to the shape of the cells within it (Fig. 2.1). There are three basic shapes of epithelial cell:

The full classification of the type of epithelium is based upon the shape of the cell and the number of layers present. There are a number of different types of epithelial tissue in the body, these include:

Ciliated epithelium – this is a more specialised epithelium consisting of a single layer of column-shaped cells (Figs 2.1, 2.3). The free surface of the cells has tiny hair-like projections called cilia whose function is to ‘waft’ foreign particles along the epithelial surface and out of the body. Ciliated epithelium lines the upper respiratory tract, where it helps to trap solid particles that have been inhaled, preventing them from entering the more distal parts of the respiratory system. The uterine tubes are also lined with ciliated epithelium, which helps to move the fertilised egg along the reproductive tract.

Stratified epithelium – this is composed of a number of layers of cells and is thicker and tougher than the other types of epithelium. It is found in areas that are subjected to wear and to friction and shearing forces, e.g. the epidermis of the skin (see p. 44). Pseudostratified epithelium (Fig. 2.3) appears to be multilayered because of the irregular positioning of the nuclei but is actually a single layer of cells. This may be found in areas such as the trachea.


Glandular tissue is a modification of epithelial tissue. The epithelium, in addition to its protective function, may also be a secretory membrane. Glands are either:

Unicellular glands – these have individual secretory cells that are interspersed throughout the tissue. The most common type is the goblet cell (Fig. 2.4), which secretes clear sticky mucus directly on to the membrane surface. The epithelium is known as a mucous membrane. Mucus traps particles, providing extra protection, and also lubricates the epithelial surface. Mucous membranes are found covering the oral cavity, lining the vagina and the trachea and in many other parts of the body.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Tissues and body cavities

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