Herbivores, Carnivores digestive systems
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Herbivores:
animals that eat vegetation. They can digest and use as food the cellulose that forms the cell walls of all plants.
Carnivores:
animals that eat herbivores. The digestion of the predator cannot break down the walls of plant cells.
Plant material is more difficult to digest than animal tissue. Consequently, the intestines of herbivores are longer and more complex than those of carnivores. Herbivores usually have a compartment (rumen or functional cecum) that contains microorganisms that break down the cellulose wall of plants.
Carnivorous animal - the dog
The dog is a pure carnivore. Since the digestive systems of all carnivores are the simplest, being essentially long pieces of tubing with a single bulge near the beginning, we will look at the dog first.
The first thing to note about the digestive systems of all carnivores is that they are remarkably similar and all function in the same way. Although they will vary in length, as carnivores come in all sizes, the total length of a carnivorous animal's digestive tract is quite short: about six times the length of the animal's body. Let's walk through the digestive tract from one end to the other to discover what each part does.
Mouth
The dog's jaw has incisors, canines, and molars in both jaws, and the molars are serrated. The jaw moves up and down. This fact, together with the underbite of the molars, indicates that they are used for tearing or crushing. The salivary glands serve only for lubrication and have no important digestive function. Food is rarely chewed into small pieces, but is "swallowed" whole.
Stomach,
The dog's stomach, the only bulge in the digestive "tube," is small, holding about four pints. Its small size gives a good estimate of the amount of food the animal can consume at any one time. The stomach has two purposes. First, it is a reservoir. Although relatively small, this is all that is necessary, since the food of a carnivore, consisting entirely of meat and fat, is nutrient-dense, allowing a small meal to last for many hours. The second function of the stomach is to subject the food to a concentrated solution of hydrochloric acid, which dissolves and liquefies it. Only food that dissolves can be digested. Different foods dissolve at different rates and leave the stomach at different rates. Those that cannot be digested—raw plant matter, cellulose, and bone—pass through the animal unchanged, while those that are too large to pass into the small intestine are regurgitated. The stomach of a dog, if full of its normal diet of meat and fat, will empty in about three hours. The stomach then rests until the next meal. Very little digestion has taken place so far, and in a carnivorous animal the stomach is not an essential organ.
The small intestines,
The small intestine, about twenty feet long in a dog, is vital. Without it, digestion could not take place and the animal could not survive. The dissolved food, called "chyme" at this stage, leaves the stomach in a series of streams controlled by a valve, the pylorus, and enters the small intestine. In the small intestine, the food is digested and enters the bloodstream. A few inches later, two ducts connect from the pancreas and liver to the small intestine. These two organs supply and deliver the enzymes necessary to break down fats and proteins into their constituent fatty acids and amino acids. Only in this form can they pass through the intestinal wall into the bloodstream. These enzymes are vital to carnivores. Those from the pancreas immediately begin to break down the chyme into its basic components and continue to do so as the chyme passes through the small intestine.
Chyme is a watery mixture, but fat will not mix with water, so special processing is required. This is where bile comes in. Bile is produced in the liver and stored in the gallbladder until it is needed. When fatty tissue is found in the small intestine, it causes the stored bile to be released, which enters the intestine through the bile duct. Bile acts as a detergent, as it emulsifies fat to make it water-soluble. This action makes the fat susceptible to digestion by digestive enzymes.
In carnivores, there are large amounts of fat in the diet, and because bile is so important, their waste is not allowed. The liver makes bile continuously, with the excess diverted to the gallbladder to be stored and concentrated until needed (for the next meal). When a hormone in the upper intestine signals that fat tissue is back in the intestine, the stored bile is forced out to perform its function.
The digestion of food in a carnivore is done by enzymes produced by glands in the animal's own body, and all the absorption of nutrients in that food is through the wall of the small intestine. This is an important consideration when we compare it later with the digestion of a herbivore.
The digestion of protein and fat, with little or no carbohydrate, in the intestines of carnivores is remarkably efficient. Experiments that have measured the amount of various nutrients eaten and compared them with the amounts passed out in the animals' excrement have shown that a healthy animal loses no more than four percent of its fat intake and only a trace of protein.
Since there is no enzyme in the carnivore capable of digesting cellulose, the material in which the cell walls of all plants are built, little or no carbohydrate digestion can occur.
The cecum.
The small intestine does not join the large intestine in a straight line, but at a right angle. At this point is a small appendage, two or three inches long, called the cecum. While this has no functional use in a carnivore, it is worth noting because it is one of the main differences between a carnivore and a herbivore.
By the time the chyme has passed through the animal's small intestine, the process of digesting and absorbing the nutrients in the food is complete. The large intestine, or colon, has only one function. It would be wasteful to allow water to escape, so the colon extracts the water and compacts the rest of the waste material from what is left of the chyme into a small, compact mass where it is stored in the rectum until finally expelled through the anus. A colon in a carnivorous animal is not essential, it is simply a convenience.
Intestinal flora.
Virtually the entire gastrointestinal tract of a carnivore is sterile. The hydrochloric acid in the stomach ensures that most bacteria and other microorganisms in ingested food are killed. Those that escape the stomach rarely survive the digestive processes - they are made of protein, after all. The colon is an exception. This, where no further digestive processes take place, tends to harbor various organisms that form certain vitamins such as pyridoxine, vitamin B-12, biotin, vitamin K, and folic acid, but since they are not absorbed through the wall of the colon, they have little effect.
The length of the gastrointestinal tract of a carnivorous animal. The intestines of any animal are usually measured after death, when its muscles are relaxed. This gives a rather misleading impression. While the animal we have been discussing measures over thirty feet when the dead dog is dissected, this is not its normal length when the animal is alive. It has been found by passing a rubber tube through a live dog, which has a similar length of intestine when dissected, that the anterior end emerges at its anus when a little more than ten feet has entered the mouth. From such measurements it is generally believed that the total length of the intestines of a carnivorous animal is probably about five to six times the length of the animal's body.
reference
1. Walter Voegtlin, The Stone Age Diet, Vantage Press, Inc, New York, NY, 1976
You can also look at:
https://en.m.wikibooks.org/…/Anatomy…/The_Gut_and_Digestion
animals that eat vegetation. They can digest and use as food the cellulose that forms the cell walls of all plants.
Carnivores:
animals that eat herbivores. The digestion of the predator cannot break down the walls of plant cells.
Plant material is more difficult to digest than animal tissue. Consequently, the intestines of herbivores are longer and more complex than those of carnivores. Herbivores usually have a compartment (rumen or functional cecum) that contains microorganisms that break down the cellulose wall of plants.
Carnivorous animal - the dog
The dog is a pure carnivore. Since the digestive systems of all carnivores are the simplest, being essentially long pieces of tubing with a single bulge near the beginning, we will look at the dog first.
The first thing to note about the digestive systems of all carnivores is that they are remarkably similar and all function in the same way. Although they will vary in length, as carnivores come in all sizes, the total length of a carnivorous animal's digestive tract is quite short: about six times the length of the animal's body. Let's walk through the digestive tract from one end to the other to discover what each part does.
Mouth
The dog's jaw has incisors, canines, and molars in both jaws, and the molars are serrated. The jaw moves up and down. This fact, together with the underbite of the molars, indicates that they are used for tearing or crushing. The salivary glands serve only for lubrication and have no important digestive function. Food is rarely chewed into small pieces, but is "swallowed" whole.
Stomach,
The dog's stomach, the only bulge in the digestive "tube," is small, holding about four pints. Its small size gives a good estimate of the amount of food the animal can consume at any one time. The stomach has two purposes. First, it is a reservoir. Although relatively small, this is all that is necessary, since the food of a carnivore, consisting entirely of meat and fat, is nutrient-dense, allowing a small meal to last for many hours. The second function of the stomach is to subject the food to a concentrated solution of hydrochloric acid, which dissolves and liquefies it. Only food that dissolves can be digested. Different foods dissolve at different rates and leave the stomach at different rates. Those that cannot be digested—raw plant matter, cellulose, and bone—pass through the animal unchanged, while those that are too large to pass into the small intestine are regurgitated. The stomach of a dog, if full of its normal diet of meat and fat, will empty in about three hours. The stomach then rests until the next meal. Very little digestion has taken place so far, and in a carnivorous animal the stomach is not an essential organ.
The small intestines,
The small intestine, about twenty feet long in a dog, is vital. Without it, digestion could not take place and the animal could not survive. The dissolved food, called "chyme" at this stage, leaves the stomach in a series of streams controlled by a valve, the pylorus, and enters the small intestine. In the small intestine, the food is digested and enters the bloodstream. A few inches later, two ducts connect from the pancreas and liver to the small intestine. These two organs supply and deliver the enzymes necessary to break down fats and proteins into their constituent fatty acids and amino acids. Only in this form can they pass through the intestinal wall into the bloodstream. These enzymes are vital to carnivores. Those from the pancreas immediately begin to break down the chyme into its basic components and continue to do so as the chyme passes through the small intestine.
Chyme is a watery mixture, but fat will not mix with water, so special processing is required. This is where bile comes in. Bile is produced in the liver and stored in the gallbladder until it is needed. When fatty tissue is found in the small intestine, it causes the stored bile to be released, which enters the intestine through the bile duct. Bile acts as a detergent, as it emulsifies fat to make it water-soluble. This action makes the fat susceptible to digestion by digestive enzymes.
In carnivores, there are large amounts of fat in the diet, and because bile is so important, their waste is not allowed. The liver makes bile continuously, with the excess diverted to the gallbladder to be stored and concentrated until needed (for the next meal). When a hormone in the upper intestine signals that fat tissue is back in the intestine, the stored bile is forced out to perform its function.
The digestion of food in a carnivore is done by enzymes produced by glands in the animal's own body, and all the absorption of nutrients in that food is through the wall of the small intestine. This is an important consideration when we compare it later with the digestion of a herbivore.
The digestion of protein and fat, with little or no carbohydrate, in the intestines of carnivores is remarkably efficient. Experiments that have measured the amount of various nutrients eaten and compared them with the amounts passed out in the animals' excrement have shown that a healthy animal loses no more than four percent of its fat intake and only a trace of protein.
Since there is no enzyme in the carnivore capable of digesting cellulose, the material in which the cell walls of all plants are built, little or no carbohydrate digestion can occur.
The cecum.
The small intestine does not join the large intestine in a straight line, but at a right angle. At this point is a small appendage, two or three inches long, called the cecum. While this has no functional use in a carnivore, it is worth noting because it is one of the main differences between a carnivore and a herbivore.
By the time the chyme has passed through the animal's small intestine, the process of digesting and absorbing the nutrients in the food is complete. The large intestine, or colon, has only one function. It would be wasteful to allow water to escape, so the colon extracts the water and compacts the rest of the waste material from what is left of the chyme into a small, compact mass where it is stored in the rectum until finally expelled through the anus. A colon in a carnivorous animal is not essential, it is simply a convenience.
Intestinal flora.
Virtually the entire gastrointestinal tract of a carnivore is sterile. The hydrochloric acid in the stomach ensures that most bacteria and other microorganisms in ingested food are killed. Those that escape the stomach rarely survive the digestive processes - they are made of protein, after all. The colon is an exception. This, where no further digestive processes take place, tends to harbor various organisms that form certain vitamins such as pyridoxine, vitamin B-12, biotin, vitamin K, and folic acid, but since they are not absorbed through the wall of the colon, they have little effect.
The length of the gastrointestinal tract of a carnivorous animal. The intestines of any animal are usually measured after death, when its muscles are relaxed. This gives a rather misleading impression. While the animal we have been discussing measures over thirty feet when the dead dog is dissected, this is not its normal length when the animal is alive. It has been found by passing a rubber tube through a live dog, which has a similar length of intestine when dissected, that the anterior end emerges at its anus when a little more than ten feet has entered the mouth. From such measurements it is generally believed that the total length of the intestines of a carnivorous animal is probably about five to six times the length of the animal's body.
reference
1. Walter Voegtlin, The Stone Age Diet, Vantage Press, Inc, New York, NY, 1976
You can also look at:
https://en.m.wikibooks.org/…/Anatomy…/The_Gut_and_Digestion
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