In atlas A, the major cavities of the body were described, as well as some of the membranes that line them and cover their viscera. We now consider some histological aspects of the major body membranes.
The largest membrane of the body is the cutaneous (cue-TAY-nee-us) membrane—or more simply, the skin (detailed in chapter 6). It consists of a stratified squamous epithelium (epidermis) resting on a layer of connective tissue (dermis). Unlike the other membranes to be considered, it is relatively dry. It retards dehydration of the body and provides an inhospitable environment for the growth of infectious organisms.
The two principal kinds of internal membranes are mucous and serous membranes. A mucous membrane (mucosa) (fig. 5.33), lines passageways that open to the exterior environment: the digestive, respiratory, urinary, and reproductive tracts. A mucosa consists of two to three layers: (1) an epithelium, (2) an areolar connective tissue layer called the lamina propria38 (LAM-ih-nuh PRO-pree-uh), and sometimes, (3) a layer of smooth muscle called the muscularis (MUSK-you-LAIR-iss) mucosae. Mucous membranes have absorptive, secretory, and protective functions. They are often covered with mucus secreted by goblet cells, multicellular mucous glands, or both. The mucus traps bacteria and foreign particles, which keeps them from invading the tissues and aids in their removal from the body. The epithelium of a mucous membrane may also include absorptive, ciliated, and other types of cells.
A serous membrane (serosa) is composed of a simple squamous epithelium resting on a thin layer of areolar connective tissue. Serous membranes produce watery serous (SEER-us) fluid, which arises from the blood and derives its name from the fact that it is similar to blood serum in composition. Serous membranes line the insides of some body cavities and form a smooth outer surface on some of the viscera, such as the digestive tract. The pleurae, pericardium, and peritoneum described in atlas A are serous membranes.
The circulatory system is lined with a simple squa-mous epithelium called endothelium, derived from meso-derm. The endothelium rests on a thin layer of areolar tissue, which often rests in turn on an elastic sheet. Collectively, these tissues make up a membrane called the tunica interna of the blood vessels and endocardium of apo = from, off, away lamina = layer + propria = of one's own apo = from, off, away lamina = layer + propria = of one's own
Saladin: Anatomy & I 5. Histology I Text I I © The McGraw-Hill
Physiology: The Unity of Companies, 2003 Form and Function, Third Edition the heart. The simple squamous epithelium that lines the pleural, pericardial, and peritoneal cavities is called mesothelium.
Some joints of the skeletal system are lined by fibrous synovial (sih-NO-vee-ul) membranes, made only of connective tissue. These membranes span the gap from one bone to the next and secrete slippery synovial fluid (rich in hyaluronic acid) into the joint.
Before You Go On
Answer the following questions to test your understanding of the preceding section:
19. Compare the structure of tight junctions and gap junctions. Relate their structural differences to their functional differences.
20. Distinguish between a simple gland and a compound gland, and give an example of each. Distinguish between a tubular gland and an acinar gland, and give an example of each.
21. Contrast the merocrine and holocrine methods of secretion, and name a gland product produced by each method.
22. Describe the differences between a mucous and a serous membrane.
23. Name the layers of a mucous membrane, and state which of the four primary tissue classes composes each layer.
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