Abdominal Regions.—For convenience of description the abdominal cavity has been divided into nine regions by means of two transverse parallel lines, the one through the ninth costal cartilages and the other just over the iliac crests, and two perpendicular parallel lines through the cartilage of the eighth rib and the middle of Poupart’s ligament on either side. These nine regions have been named as follows: The right and left [hypochondriac regions] up under the ribs with the epigastrium between, the right and left [lumbar regions] next below with the [umbilical] between, and the right and left [inguinal] with the [hypogastric] between. Others divide it into quadrants by one line drawn across and another down through the umbilicus. The contents of the abdomen in full are the stomach, intestines, liver, gall-bladder, spleen, pancreas, kidneys, suprarenal capsules, and the great vessels, that is, the organs of digestion and excretion. When distended the bladder extends up into the abdominal cavity, as does the uterus also when enlarged.
Salivary Digestion.—Although most of the digestive organs are situated in the abdomen, the food enters the body through the mouth, where its prehension is a voluntary act. Here digestion also begins and from the first the process is a double one, mechanical and chemical, mechanical digestion consisting largely of muscular movements by which the food is ground up and carried through the digestive tract. Thorough mastication or grinding of the food by the teeth is necessary, while the tongue assists by moving the food about and by mixing it thoroughly with the saliva, a viscid fluid composed of water and salts and having a slightly alkaline reaction. The saliva is secreted by the parotid, sublingual, and submaxillary glands, and serves to soften and dissolve the food and by virtue of its unorganized ferment, ptyalin, to convert starch into sugar. Upon proteins and fats it has practically no digestive action. Moderate warmth and an alkaline medium favor its action, while extremes of heat or cold or an acid medium hinder it. There is little absorption in the mouth, though starch, nicotine, and alcohol may be absorbed in small quantities.
The Pharynx.—When the food is ready for deglutition or swallowing, it is thrust back into the pharynx, a somewhat conical, musculo-membranous sac, situated, base upward, behind the nose and mouth and behind, but somewhat above, the larynx. The pharynx is about four and a half inches long and ends on a level with the cricoid cartilage in the esophagus or gullet. It is attached to the vertebræ at the back and opens in front into the mouth. The posterior nares, the Eustachian tubes, and the larynx also open into it, the last being protected by the epiglottis, which closes during deglutition to prevent food from entering the air passages, just as the soft palate is drawn back to prevent regurgitation of food into the nose. There are three coats to the pharynx: 1. a mucous coat continuous with that of the mouth and ciliated down to the floor of the nares; 2. a fibrous coat, and 3. a muscular coat containing among others the constrictor muscles which serve to carry the food down to the esophagus. Its arteries are branches of the external carotid and its nerves come from the spinal accessory and the sympathetic. Occasionally a foreign body gets lodged in the pharynx just out of reach of the finger and threatens strangulation. Retropharyngeal abscess on the posterior wall occurs rarely.
Fig. 53.—Position of the thoracic and abdominal organs,
front view. (Morrow.)
The Esophagus.—From the pharynx the food passes to the cardiac orifice of the stomach, opposite the tenth dorsal vertebra, through the esophagus, a muscular tube about nine inches long, which collapses when empty, its lumen then appearing as a transverse slit. It, too, has three coats: 1. an inner mucous coat; 2. an areolar coat, and 3. a muscular coat, the muscles being arranged in two sets, an outer longitudinal layer and an inner circular layer. By a series of rhythmic contractions, especially of the circular fibers, the food is pushed along, though sometimes with liquid food there is no peristaltic action of the esophagus, the pharyngeal muscles alone sending it to the stomach. At the lower end of the esophagus an especially strong band of circular muscle fibers form a sort of sphincter, which prevents the regurgitation of food. The whole act of swallowing is a reflex, not a voluntary act and is due to irritation set up by the stimulus of the foreign body, the food. Stricture of the esophagus is common and may be of three kinds: 1. spasmodic, occurring in nervous women; 2. fibrous, due to scar tissue, or 3. malignant, due to cancer.
The Stomach.—[The stomach] is a pear-shaped dilatation of the alimentary canal, lying under the [liver] and diaphragm in the epigastrium and left hypochondrium and connecting the esophagus with the small intestine. It lies largely behind the ribs, but the greater curvature is only two fingers’ breadth above the umbilicus and can be manipulated through the skin. The cardiac end, into which the esophagus enters, is the larger and points upward to the left. The lesser and lower end, known as the pylorus, is at the right and its opening into the small intestine is guarded by the pyloric sphincter. The lesser curvature is concave and on the upper surface; the greater, convex and on the under surface. The great omentum is attached to the latter.
In size the stomach varies more or less, that of a man generally being larger than that of a woman, but it is usually about ten inches long and four or five inches across. It has a capacity of about five pints and serves as a storehouse for food.
The stomach has four coats: 1. a serous coat derived from the peritoneum; 2. a muscular coat of three layers with longitudinal fibers continuous with those of the esophagus, circular fibers, and oblique fibers; 3. an areolar coat, and 4. a mucous coat, which, when the stomach is empty, is thrown into longitudinal folds or rugæ, and whose surface is covered with glands, the gastric glands, for the secretion of the digestive fluids.
The arteries come from the celiac axis and the nerves from the pneumogastric and the solar plexus.