Digestive tract

“ Comminution of hard food is of first importance, undoubtedly, but insalivation and neutralisation or alkalinisation are, seemingly, much more easily and quickly accomplished in the mouth than farther on in the alimentary canal. The intestines can do all in the way of digestion, even if the mouth and stomach are passed and their assistance in the digestive process is entirely neglected, but it is done at tremendous disadvantage in the supplementary digestive tract of the intestines. ”

“ In the animal the absorbent surfaces of these organs are internal; in the plant, external. In nearly all the higher animals there is a mouth opening, through which solid as well as liquid food may pass into the digestive cavity, which is furnished with specialized glandular appendages, such as the salivary glands, liver, etc. Within the digestive tract the food is elaborated and prepared for digestion and digested, and the indigestible refuse is discharged from the body through a definite anal opening. ”

“ The integrity of the functions of the intestines is of supreme importance, for it is here that absorption and assimilation of most 183of our food occurs. If our intestines are not in perfect order we shall soon waste and dwindle away, even within a short period, and sometimes very rapidly. Thus if we wish to retain our strength we must treat the intestine with the greatest care. This is especially the case in old age, for then an atrophy of the glandular mechanism of the digestive tract, stomach, and intestines, takes place. ”

“ The normal stool is a mixture of— (a) Water; (b) undigested and indigestible remnants of food, as starch-granules, particles of meat, plant-cells and fibers, etc.; (c) digested foods, carried out before absorption could take place; (d) products of the digestive tract, as altered bile-pigments, mucus, etc.; (e) products of decomposition, as indol, skatol, fatty acids, and various gases; (f) epithelial cells shed from the wall of the intestinal canal; (g) harmless bacteria, which are always present in enormous numbers. ”

“ What might seem to be a stupor comes over the digestive tract, and while the nervous influence which determines digestion ceases entirely, that which tends to bring about the expulsion of material from the digestive tract may become more active and all the material contained in the digestive viscera may, in a short time, be expelled. ”

“ Ordinarily, the digestive tract acts like a sponge which absorbs the elements of nutrition; but in acute diseases the process is reversed, the sponge is being squeezed and gives off large quantities of morbid matter. The processes of digestion and assimilation are at a standstill. In fact, the entire organism is in a condition of prostration, weakness and inactivity. The vital energies are concentrated on the cleansing and healing processes. ”

“ You are aware of the irritation that a grain of sand will set up when it comes in contact with the mucous membrane of the eye. Then can you not realize that you will torment the forty-five feet of intestinal mucous membrane with like indigestible stuff? It is estimated that ten per cent. of the really suitable food is residue matter with which the digestive tract has to deal and get rid of with as much economy and as little friction as possible. ”

“ In the former this segment of the canal functions as an accessory digestive apparatus and hence, as we will see, often develops accessory structural modifications, such as a large cæcum and spiral colon, while in the latter it acts almost solely as a canal for the evacuation of the indigestible remnants.
Again, the large intestine is better developed in the higher animals, in mammalia and to a lesser degree in birds, in whom the functional demands for nutrition are active and require that a relatively large amount of food should pass through the digestive tract in a given time. ”

“ Experiments with pigs show that if large amounts of coarse, granular foods are consumed, the tendency is for the digestive tract to become inflamed and less able to exercise its normal functions. Coarsely granulated foods have a tendency to pass through the digestive tract in less time than those that are finely granulated, due largely to increased peristaltic action, and the result is the food is not retained a sufficient length of time to allow normal absorption to take place. ”

“ Ruminating animals, or animals which chew the cud, such as the Cow, have several stomachs, and the food undergoes mastication several times, at each time being passed into a different stomach, before being finally acted upon by the gastric juice, after which it is transmitted through a long tract of intestines. This is an example of the most complex 360 digestive organ fitted to act upon hard and fibrous food, which must be subjected to the action of several menstrua preparatory to its being acted upon by the gastric juice. ”

“ Of all domestic animals the most simple digestive tract occurs in the dog. These variations in the development of the different organs of digestion, together with the difference in the character of the feed and method of feeding, cause a variation in the kind of diseases met with in the different species. The complicated stomach of ruminants predispose them to diseases of this portion of the digestive tract. Because of their complicated intestinal tract solipeds are prone to intestinal disease. ”

“ People have heard much of the flora of the digestive tract, until they have come to think with anxiety of the almost infinite number and multitudinous variety of the minute plant life that finds a habitat in the human intestine. Most people think that all of these are, in tendency at least, {96} harmful, and are only kept from being positively dangerous by the overwhelming vital activity of the mucous membrane and the secretions which keep them from exerting their malign activity. ”

“ The histology of the œsophagus and the other regions of the digestive tract will be described later.
Fig. 34. Digestive System of A. Mississippiensis.
bd, bile duct; bs, bile sac; c, cloaca; e, œsophagus; f, larger or fundic region of stomach; h, hyoid apparatus; l, liver; p, smaller or pyloric region of the stomach; pa, pancreas; r, rectum; s, small intestine; t, tongue; tr, trachea.
The Stomach
The stomach, as is well known, is made up of two distinct parts; that on the animal’s left, into which the œsophagus opens, is many times larger than the part from which the small intestine leads. ”

“ During cooking, as discussed in Chapter II, extensive physical and chemical changes occur, and these in turn affect digestibility. When the cooking has not been sufficient to mechanically disintegrate vegetable tissue, the digestive fluids fail to act favorably upon the food. Cooking is also beneficial because it renders the food sterile and destroys all objectionable microörganisms which, if they remain in food, readily undergo incubation in the digestive tract, interfering with normal digestion. ”

“ We have seen that the intestinal tube of all vertebrates is the product of two of the embryonal blastodermic layers, the entoderm and mesoderm. The former furnishes the characteristic and cardinal elements of the digestive tract, viz., the secretory and absorbing epithelium of the mucous membrane and of the accessory digestive glands, the liver and pancreas. ”

“ A great variety of germs are found in drinking water, and no doubt countless numbers are taken into the digestive tract, and the principal reason why pathological conditions do not occur more frequently is on account of the germicidal qualities of the gastric juice. ”

“ It must also be borne in mind that the indigestible food residues, as finally voided by the animal, have played an important mechanical part as an aid to digestion of those constituents more readily attacked in the digestive tract of animals. ”

“ The patient may have nausea, vomiting, pain or even more severe symptoms. The severity of the symptoms and their effect upon the patient depend somewhat upon the average vigor or stability ordinarily displayed by the digestive tract under a lesser strain. People with so-called delicate digestions may be greatly upset by combinations of food which others are able to cope with and suffer little or no inconvenience. ”

“ The mucous and serous membranes of the canal and the glandular elements of the associated organs are the parts most subject to inflammatory affections. Among the several sections of the digestive tract itself, the oesophagus and jejunum are singularly exempt from inflammatory processes; the fauces, stomach, caecum and appendix, ileum, mouth and duodenum (including the opening of the common bile-duct) , are more commonly involved. Stomatitis, or inflammation of the mouth, Inflammatory lesions. ”

“ The oesophagus expands into a curious gizzard, which is armed internally with large horny processes, some broad and thick, others spinous, fitted to act as crushing instruments. From this we pass to a stomach and a coil of intestine embedded in the lobes of a voluminous liver; a caecum of large size is given off near the commencement of the intestine. The liver opens by two ducts into the digestive tract. ”

“ Hence the reason why on leaving a warm room to enter a cold frosty air there is an immediate action of the visceral organs from pressure of blood on them, and not unfrequently a tendency to diarrhoea from temporary congestion of the digestive tract. ”

“ A cæcal pouch or diverticulum in some form at the junction of mid- and hindgut is a very common and widely distributed mammalian character. The activity of the tissue-changes in warm-blooded animals, and the consequent necessity for a rapid and complete digestive process, account for the structural modifications of the alimentary tract so commonly encountered among these forms. On the other hand, in the lower cold-blooded vertebrates, notably in fishes and amphibians, the metabolism is slow and the alimentary canal usually simple. ”

“ Thus we know that the stimulus of food in the stomach sends a chemical substance from one ductless gland in the digestive system chasing through the blood to another gland which prepares a different digestive secretion further on. ”

“ And it is not at all strange that they should, since there is so much pressure from within, so much pressure downward, and so much pressure from without—all through the requirements of fashion, indulgence, and ignorance. But the stomach, upper portion of the duodenum, and small intestine, cæcum, the ascending colon, and especially the transverse colon and sigmoid flexure, are susceptible to various forms of displacement, inhibiting the ready flow or passage of food stuffs, gases, and feces from one segment of the digestive apparatus to another, until the vent is reached. ”

“ The lack of a sufficiently vigorous flow of blood is followed by deficient secretion of digestive agents from the glandular elements involved, by decreased motility of the muscular coats of the stomach and bowel, and lessened adaptability throughout for dealing with even slight irregular demands on their powers. ”

“ I refer to the production of gastric juice in the empty stomach, as a result merely of the swallowing of food in the so-called sham feeding of an œsophagotomised dog. When one takes into consideration the absolute independence of this factor, and the intensity of the effect, which makes itself evident in the secretion of a large quantity of juice of high digestive power, the exciting agency which brings about such secretion must be recognised as one of the most important and effective processes in gastric digestion. ”

“ Adjuvants to Digestion.—In atony of the stomach the gastric mucous membrane responds feebly to the stimulus of food. There is failure in both muscular movement and gastric secretion, with slowness of digestion as a result. To meet this condition we seek to increase the digestive power by the addition of certain principles natural to the digestive process—viz. the mineral acids, pepsin, and pancreatin. Of these acids, the hydrochloric should be preferred, because it is the natural acid of the gastric juice. ”

“ Not only that the progress of digestion is thus interrupted, not only that the body derives no strength from the inert mass of ingesta, but that mass, by undergoing a putrid instead of peptic decomposition, vitiates the humors of the system it was intended to nourish, irritates the sensitive membranes of the stomach, and gradually impairs the vigor of the whole digestive apparatus. ”

“ If the eliminating power of the intestinal canal is normally active, the fortunate individual may eat abundantly, or really in excess of the requirements of the system, and still escape any ill effects, such as indigestion, biliousness, acid in the urine, etc. The hearty consumer of food whose bowels eliminate properly may suffer a loss of appetite, but it will not be accompanied with foulness of the digestive apparatus.
When all the organs of the body perform their functions in a normal manner, no part of the structure is in immediate need of repair. ”

“ The process of digestion, as the food passes from one end of the tract to the other, is performed by the aid of the secretions of various glands, which open into the alimentary canal at different points in its course. The principal of these are the salivary glands, situated on the pharynx and oesophagus, and the liver, biliary or hepatic gland, connecting with the stomach. With these may be considered the anal and ink-glands, which, in certain genera, connect with the terminal portion of the rectum. ”