Unit 10

Pre-text assignments

1 Learn the key words and phrases:

innervation, distinct layers, innermost tissues, mucous membrane, folds, lumen, tubular invaginations, visceral peritoneum

2 Memorize the explanation to the terms:

break to separate into parts

absorb to take in and use as nourishment

moist to wet moderately

lubricate to make smooth or slippery

The Alimentary Canal

The alimentary canal is a muscular tube about 9 meters long that passes through the body's ventral cavity. Although it is specialized in various regions to carry on particular functions, the structure of its wall, the method by which it moves food, and its type of innervation are similar throughout its length.

The wall of the alimentary canal consists of four distinct layers, although the degree to which they are developed varies from region to region. Beginning with the innermost tissues, these layers, include the following:

1 Mucous membrane (mucosa). This layer is formed of surface epithelium, underlying connective tissue (lamina propria), and a small amount of smooth muscle. In some regions, it develops folds and tiny projections that extend into the lumen of the digestive tube and increase its absorptive surface area. It may also contain glands that are tubular invaginations into which the lining cells secrete mucus and digestive enzymes. The mucosa protects the tissues beneath it and carries on absorption and secretion.

2 Submucosa. The submucosa contains considerable loose connective tissue as well as blood vessels, lymphatic vessels, and nerves. Its vessels nourish the surrounding tissues and carry away absorbed materials.

3 Muscular layer. This layer, which is responsible for the movements of the tube, consists of two coats of smooth muscle tissue. The fibers of the inner coat are arranged so that they encircle the tube, and when these circular fibers contract, the diameter of the tube is decreased. The fibers of the outer muscular coat run lengthwise, and when these longitudinal fibers contract, the tube is shortened.

4 Serous layer (serosa). The serous, or outer covering of the tube is composed of the visceral peritoneum, which is formed of epithelium on the outside and connective tissue beneath. 6 The cells of the serosa secrete serous fluid, which keeps the tube's outer surface moist. This lubricates the surface so that the organs within the abdominal cavity slide freely against one another.

Post-text assignments

1 Answer the following:

1 What is the alimentary canal?

2 Distingwish between mucosa and submucosa.

3 Distingwish between muscular layer and serous layer.

2 Ask questions using the parenthesized words:

1 The alimentary canal is a muscular tube about 9 maters long. (What size) 2 The wall of the alimentary canal consists of four disfinct layers. (How many) 3 Mucous membrane is formed of surface epithelium and a small amount of smooth muscle. (What ... of) 4 The mucosa protects the tissues beneath. (What) 5 The fibers of the outer muscular coat run lengthwise. (How) 6 The cells of the serosa secrete serous fluid. (What)

3 Summarize the characteristics of these layers:

Layer	Composition	Function
Mucous membrane	Epithelium, connective tissue, smooth muscle	Protection, absorption, secretion
Submucosa	Loose connective tissue, blood vessels, lymphatic vessels, nerves	Nourishes surrounding tissues, transports absorbed materials
Muscular layer	Smooth muscle fibers arranged in circular and longitudinal groups	Movements of the tube and its contents
Serous layer	Epithetium, connective tissue	Protection