Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 39

The term squamous means resembling the scale of a fish, therefore squamous cells are described as being thin and flat in appearance (Figure 1.8A). This tissue is found in multiple locations within the body including the alveolar walls of the lung, endothelial lining of blood vessels and capillary walls, and lining the major serous membranes and serous layers of organs.

Since the cells of squamous epithelium are so thin and flat, they are perfectly adapted to locations where simple diffusion takes place such as the alveoli of the lungs. Their thinness also imparts elasticity to the alveolar wall, allowing inflation of the lungs when air is inspired.

From a surface (apical) view, squamous epithelial cells have an appearance that resembles ‘crazy paving’, and for this reason this tissue is also commonly referred to as pavement epithelium. Many of the body’s internal membranes, such as the peritoneal membrane which lines the abdominopelvic cavity, the pericardial membranes that surround the heart and the pleural membranes that surround the lungs, have a layer of squamous epithelial cells associated with them. These membranes are referred to as serous membranes since their resident squamous cells secrete a thin watery fluid called serous fluid.

This fluid is very slippery and acts as a natural internal lubricant within the body, reducing friction between the visceral organs during bodily movement. Many of the body’s internal organs such as the outer layers of the gut (serosa) and the uterus (perimetrium) also have a thin serous layer composed of squamous cells, which contribute further to the secretion of this internal lubricant. When major body cavities are opened during surgery this serous fluid is clearly visible as a glistening shiny surface coating the internal organs.