Dog Digestive System
One of the functions of the blood is to transport nourishment to the body’s cells. The nutrients are prepared for the blood by the digestive system.
The Teeth and Mouth. Mouths of dogs differ markedly among the several species, yet there is a general similarity. The lips are the portal to the mouth. They are also remarkably sensitive organs of touch for some dogs, such as the horse, which can, with its coarse lips, feel among a lot of debris in a manger for a single oat grain! Monkeys to use their lips with singular effectiveness. Fishes rely on them. Dogs, cats, rabbits, guinea pigs, mice, and rats, on the other hand, seem to use their lips almost entirely for their primary purpose to retain the food as it is chewed and the mouth juices, or secretions.
In each species of pet the teeth are unique in some respect number, arrangement, and length yet in major respects there is an unusual similarity. Whereas humans frequently need dental care for cavities in their teeth, dogs develop very few. Nearly all their tooth troubles stem from bacterial infections or defective diets. What accounts for their sound teeth?
Chewing hard foods can’t be the reason, because many dogs are fed soft, mushy diets all their lives, and their teeth, though covered with tartar, do not decay. And most dogs’ teeth are never cleaned. The difference is to be found in the structure of their teeth. Many years ago to investigate the effect of sweets on dogs’ teeth. Diet and heredity determine the quality of teeth.
A dog has two sets of teeth. The first, or the milk teeth, fall out after their roots are partially resorted by the body at about halfway through the puppy’s growing period. The eruption of the new teeth takes place so rapidly that it often causes loss of weight in growing dogs and fever may sometimes accompany the teething.
Anatomists and students of natural history have a method of representing the number and arrangement of teeth of a species. Examples of the dental formulas of all our common pets follow.
The front “biting-off” teeth arc is called the incisors. A dog and a cat have three on each side of the midline of the upper jaw and three on the lower. Observed from the front, there appear to be six even teeth Gina row in the upper and lower jaws.
The part of the tooth above the gum is called the crown, the part between the crown and root is called the neck, and the part embedded in the socket is called the root. Some teeth have one straight root, some several. More than half the length of each canine tooth is embedded inside the gums; the roots of the teeth are strong and exceedingly difficult to extract.
Animal teeth are remarkably tough. When one sees a dog crush Allaire, hard, flinty bone or a squirrel gnaw through a hickory nut, or a raccoon cracks a nut that few of us would want to risk our molars on, our respect for dog teeth deepens.
Enamel adds to the hardness and strength and covers a softer substance called dentine. The root has no enamel covering. Inside each tooth, there is a pulp, a structure with nerves and blood vessels. These structures seldom give way, but pets can and do have tooth and gum troubles even though these rarely have anything to do with cavities. If a dog is sick with a fever-causing disease during teething, the enamel fails to deposit on the teeth. By observing the pits or rings on the canine teeth, for instance, anyone can tell at what time the puppy was sick. The whole period of replacement is not more than forty-five days. In dogs the upper-middle incisors erupt at close to fourteen weeks of age; the canines at about eighteen weeks. Thus, if you see a five-year-old dog with just the tips of the canines devoid of enamel and the lower part of the enamel missing on the incisors, you know it was sick at about four months of age. The teeth may thus form a chart of puppy sickness. It used to be said that pitted teeth in dogs were “distemper teeth.” Pitted teeth can be caused by any one of several diseases, some quite mild.
The teeth of no two species are exactly alike. It has been said that the natural diet of any species of dog can be told by examination of the teeth. This is probably true. Long, sharp tusks like those of cats or raccoons would indicate that the dog’s natural prey was some small dog easily killed and eaten. Dog’s teeth are those of carnivores. The long, powerful tusks help a dog pull the skin off a carcass, tear muscles loose, or rip out organs, while the arrangement of the back teeth for cutting or shearing would suggest that they were once meant to cut off pieces that the canine teeth had torn loose. The molars also have some flat surfaces that indicate usefulness in crunching grains.
A dog bolts its food, usually without making any pretense of chew-in. It will swallow anything small enough to go down its extraordinarily elastic gullet. It is because a dog does bolt everything you give it that it may not digest some foods very well. All other pets, except fish, do a much better job of mastication. Some fishes swallow other fishes whole. Birds, of course, have no teeth, so the problem doesn’t arise.
Glands below or behind the mouth of all dogs secrete a fluid called saliva which in some dogs contains a starch-digesting sub-stance. Dogs and cats have very little. This explains in part why it is so important to cook foods such as potatoes–to break up the starchy granules before feeding them to these pets.
The roof of the mouth has a hard surface, the hard palate, going as far back as the last teeth and made up of ripples, or bars, extending across the mouth. Behind the teeth the roof (soft palate) is flabby. By the time a pet’s food reaches the soft palate, it is practically in the throat.
The Tongue. The tongue, the principal organ for moving food into the mouth, is also the primary taste organ. Taste is experienced by the reaction to chemical stimuli of “taste buds,” or sensitive areas, which stud this organ and produce the sensations of saltiness, sweetness, bitterness, and acidity. The taste buds are situated all over the tongue but are more abundant in the tip and at the back, in the throat proper.
The Throat. The delicate business of getting food correctly started down the esophagus and not the windpipe is accomplished in the throat by the pharynx and larynx. The esophagus is located above the windpipe (trachea). An arrangement called the epiglottis, which is part of the larynx, closes over the windpipe as food and fluid descend the esophagus, then drops down to allow the passage of air.
Peristalsis. The only so-called voluntary muscles involved in digestion are in the lips, throat, and anus, and even these are partly involuntary. Physiologists regard the inside of the alimentary tract, a tube with valves and enlargements, as continuous with the skin of the outside of the body.
Once the food is swallowed, a constriction in the esophagus starts behind it and, as it progresses, forces the bolus (lump) of food into the stomach. The progress may be upward. A dog drinks with its head downward, and the fluid is moved upward for some distance before it goes down into the stomach. The contractions that pass along the tube are called peristalsis.
The Stomach. The ingested food travels down the gullet and into the stomach, which has walls sufficiently elastic to accommodate the varying amounts of food swallowed, and this wavelike movement con-tines and mixes the stomach’s juices with the food. Here some digestion of food takes place through the action of glands that pour into the stomach an acid liquid that helps digest proteins and fats. Starch digestion, begun by salivary enzymes, stops when the food in the stomach becomes acid, but few dogs rely on this kind of digestion.
The Intestines. When the exit valve of the stomach, the pylorus, opens, the food passes into the small intestine in sausage-like gobs pro-duce by the constrictions of the stomach. Soon other constrictions may start and cut the sausages in half, but persistently this process pushes the intestinal contents along through the whole length of the intestine as digestion continues.
The duodenum, a thickened area of unrolled intestine that starts at the stomach, receives via two ducts, or tubes, two important substances. One of these is bile, which is made in the liver and stored in the gallbladder. Bile breaks up fat into infinitesimal globules that have a laxative effect on the food. The yellow substance that a dog vomit is both the stomach contents and the bile that has been forced backward into the stomach by regurgitation.
The second duct transmits more stars-digesting substances manufactured in the pancreas. These enzymes turn starches into dextrin, which, as the food is pushed along, is further broken down into glucose by another substance excreted by the small intestine itself. The glucose is then absorbed through the intestines and winds up in the bloodstream. Glucose is also the sugar of grapes and corn syrup. And so in this way, digestion transforms the carbohydrates in the food into a form transportable by the blood. Proteins and fats are also reduced to their parts, amino acids, and fatty acids; as such they too can pass through the intestinal walls and into the lymph and blood.
Absorption of materials from the intestine is increased by a unique arrangement. The velvety inner surface is studded with microscopic, short, hairlike projections called villains. Each one, while minute in itself, increases the surface of the intestine a little, and in the aggregate,, these tiny projections increase the area of the intestines immensely.
How the inside of a dog’s intestine appears when magnified to show thrill. This arrangement increases the absorbing surface of the intestine enormously.
This efficient “factory” of the digestive system is like an automobile assembly line running backward, with the cars being taken to pieces bit by bit, instead of being built up. As it passes through the digestive system the whole mass of food that entered the mouth is reduced to its essential parts fatty acids, glucose, and amino acids and these disassembled products are absorbed into the blood.
The Liver. The liver is the largest solid organ of the body. It lies in front of the stomach and just behind the diaphragm, which is the partition separating the abdominal cavity from the thoracic cavity, and is constantly massaged by the regular inhalations and exhalations caused by breathing. The healthy liver is dark red with a glistening surface and several lobes, the number depending on the species. The activities of the liver are not limited to digestion; it is also ap rime organ of regulation and manufacture. Bile comes from the liver. Besides aged red blood cells, bile contains bile salts, cholesterol, lecithin, fat, mucking, and pigments.
Urea, another liver product, is made by converting ammonia left over from protein metabolism (chemical changes). Bacteria are destroyed in the liver to twosome extent, too, as they are in the lymphatic system and spleen. The liver is essential as a sugar regulator for the body. If for example, glucose were absorbed from the intestine in greater quantities than the body could use, the liver would then change it into glycogen (dog starch) and store it. When the blood sugar level drops too low, the liver obliges by releasing glucose from the conversion of glycogen. When the gall duct, or gallbladder, becomes obstructed or the bile cannot escape, the pigment gets into the blood, causing the skin to turn a yellow color. Jaundice, as it is called, is not a disease but a condition or a symptom.
Another function of the liver is the absorption of fat, which is deposited in the tissues of the body to be used when needed.
The Pancreas. Besides furnishing enzymes (digestive ferments), the pancreas regulates the power of the body to handle blood sugar. In this task, it functions with the liver, which, stores up or liberates glucose. Tiny cells called the islets of Angoras in the pancreas manufacture insulin, a substance that in some unknown way regulates the percentage of glucose in the blood. If it is too much, it causes the liver to store it; if too little, the pancreas sees that glucose is called out. A lack of insulin causes diabetes mellitus or sugar diabetes. The excess sugar escapes into the urine and may be measured. The disease also causes an increase in thirst and the amount of urine excreted.
Final Steps in Digestion. What remains of the food after it has traveled through the small intestine is deposited through a valve into the large intestine. Here excess water is absorbed, and a huge growth of bacteria takes place. In some species, it has been estimated that over half the feces is living and dead bacteria. The more unassimilated food ends up in the colon, the more there is for bacteria to work on. There are also more products of bacteria to be absorbed by the body along with the surplus water. This is another good reason for not overfeeding and underexercising pets.
Blood also acts as a vehicle for transporting substances known as hormones, produced by the body regulators, only one of which is considered the pancreas. For the most part, these regulators are ductless glands, that is, glands lacking an outlet except back into the blood. Though the spleen and lymph glands are also ductless, they do not secrete hormones. The important, strictly ductless glands are the pituitary, adrenal, thymus, thyroid, and parathyroid. Salivary glands are good examples of ordinary glands because they have ducts that lead their products away from the glands; in this case, saliva is secreted into the mouth.
Some glands, like the pancreas, are a combination of ductless and ordinary glands and are considered body regulators. The important mixed ductless and ordinary glands are the pancreas, ovaries, and testicles.
See more: Dog Drugs and the Reproductive System
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