Evolutionary Summary of a Horse’s Digestive System
Horses are known as post gastric fermenters meaning that microbial fermentation occurs in their cecum which is after the stomach (gastric). This is beneficial to horses because as an animal of prey with a strong “fight or flight” response horses are constantly on the move and cannot spend long periods of time consuming vast amounts of food or “chewing their cud”. Horses cannot vomit/regurgitate feed due to the one directional movement of the esophagus preventing them from evolving into ruminants. Horses inability to ruminate requires horses to spend a substantial amount of time masticating (chewing) their food before they swallow. Because horses have to spend a large amounts of time masticating they cannot consume vast amounts of feed in short periods of time. While horses were evolving the only food available/edible must have been plants with high cellulose concentrations and the horses who survived were those that could digest cellulose through microbial fermentation. We know now that horses ferment feed in their cecum and the reason the cecum is enlarged is because the degradation of cellulose through microbial fermentation requires several hours to occur. This means in order for microbial fermentation to occur the cecum must be large enough to store chyme for several hours. The stomach is the exact opposite of the cecum. Since horses graze small amounts of feed throughout the entire day their stomach does not expand or contain feed for long periods of time. This either led to the horse’s stomach shrinking, or as the horse evolved their body size increased but their stomach size did not.
The enzyme found is saliva is amylase. The purpose of amylase is starch break down. Since horses consume highly fibrous plants that can only be broken down by microbial fermentation amylase in there saliva would not do them any good. Since horses have no need for amylase they have evolved over time not to produce enzymes in their saliva.
Horses do not have gallbladders which make sense since horses are constantly eating. This means feed is endlessly traveling through their small intestine and there is no need for a horse to store bile. Bile is produced in the liver and directly secreted into the small intestine. As far a evolution goes horses may never have had gallbladders or having gallbladders delayed bile secretion disrupting nutrient digestion and absorption. Through natural selection horses with the most beneficial digestive systems survived.
Horses are known as post gastric fermenters meaning that microbial fermentation occurs in their cecum which is after the stomach (gastric). This is beneficial to horses because as an animal of prey with a strong “fight or flight” response horses are constantly on the move and cannot spend long periods of time consuming vast amounts of food or “chewing their cud”. Horses cannot vomit/regurgitate feed due to the one directional movement of the esophagus preventing them from evolving into ruminants. Horses inability to ruminate requires horses to spend a substantial amount of time masticating (chewing) their food before they swallow. Because horses have to spend a large amounts of time masticating they cannot consume vast amounts of feed in short periods of time. While horses were evolving the only food available/edible must have been plants with high cellulose concentrations and the horses who survived were those that could digest cellulose through microbial fermentation. We know now that horses ferment feed in their cecum and the reason the cecum is enlarged is because the degradation of cellulose through microbial fermentation requires several hours to occur. This means in order for microbial fermentation to occur the cecum must be large enough to store chyme for several hours. The stomach is the exact opposite of the cecum. Since horses graze small amounts of feed throughout the entire day their stomach does not expand or contain feed for long periods of time. This either led to the horse’s stomach shrinking, or as the horse evolved their body size increased but their stomach size did not.
The enzyme found is saliva is amylase. The purpose of amylase is starch break down. Since horses consume highly fibrous plants that can only be broken down by microbial fermentation amylase in there saliva would not do them any good. Since horses have no need for amylase they have evolved over time not to produce enzymes in their saliva.
Horses do not have gallbladders which make sense since horses are constantly eating. This means feed is endlessly traveling through their small intestine and there is no need for a horse to store bile. Bile is produced in the liver and directly secreted into the small intestine. As far a evolution goes horses may never have had gallbladders or having gallbladders delayed bile secretion disrupting nutrient digestion and absorption. Through natural selection horses with the most beneficial digestive systems survived.
Evolutionary Summary of a Cow’s Digestive System
Cows are part of a larger group of successful herbivores known as ruminants. The defining characteristic of ruminants is the ability ferment their food in a four compartment stomach. The process starts by chewing, swallowing, regurgitating, re-chewing, and re-swallowing their food. This process is known as "chewing the cud". This cud then makes its way to the rumen, where various microbes (mostly bacteria and also protozoa, yeast and fungi) start the fermentation process by breaking down the cud from protein and carbohydrates into volatile fatty acids and other gases.
Ruminants evolved many physiological features that enabled them to survive harsh, varying conditions, like fluctuating seasons and drought. They have a physiological niche that allow them to be less selective about the type of food they consume. Since they are able to process otherwise indigestible plant material that many species cannot consume successfully, they have a larger variety of food with less competition. Due to the fermentation process, as well as filtering of food particles, they are able to consume varying sizes and plants that will inevitably be broken down by microbes in the rumen.
Cows are part of a larger group of successful herbivores known as ruminants. The defining characteristic of ruminants is the ability ferment their food in a four compartment stomach. The process starts by chewing, swallowing, regurgitating, re-chewing, and re-swallowing their food. This process is known as "chewing the cud". This cud then makes its way to the rumen, where various microbes (mostly bacteria and also protozoa, yeast and fungi) start the fermentation process by breaking down the cud from protein and carbohydrates into volatile fatty acids and other gases.
Ruminants evolved many physiological features that enabled them to survive harsh, varying conditions, like fluctuating seasons and drought. They have a physiological niche that allow them to be less selective about the type of food they consume. Since they are able to process otherwise indigestible plant material that many species cannot consume successfully, they have a larger variety of food with less competition. Due to the fermentation process, as well as filtering of food particles, they are able to consume varying sizes and plants that will inevitably be broken down by microbes in the rumen.
Evolutionary Summary of a Hippo’s Digestive System
The hippo is a pseudo-ruminate because it does not chew the cud, but benefit from the rumination. It has a three-chambered stomach instead of a four-compartment stomach in ruminants. However, these multiple-chambered stomachs function similarly that the first chamber house contains cellulose-digesting microbes that assist with rumination. In the hippo stomach, the parietal blind sac is the place where colonies occur.
Here is a detailed structure of hippo stomach. The glandular stomach is the abomasums chamber in ruminants, which is the true stomach that secrets HCl, pepsin and other digestive enzymes.
(D, duodenum; O, oesophagus;CC, connecting chamber;
GS, glandular stomach; PB, parietal blind sac)
Although hippos have a ruminant-like digestion, they do not gain maximum benefit from this arrangement because they do not regurgitate the food. This makes hippos have a less sufficient digestive system that extract less nutrition from a leafy plant diet compared to a similarly-sized ruminant obtain from the same meal. Hippos overcome this by living a low energy expenditure lifestyle.
The hippo is a pseudo-ruminate because it does not chew the cud, but benefit from the rumination. It has a three-chambered stomach instead of a four-compartment stomach in ruminants. However, these multiple-chambered stomachs function similarly that the first chamber house contains cellulose-digesting microbes that assist with rumination. In the hippo stomach, the parietal blind sac is the place where colonies occur.
Here is a detailed structure of hippo stomach. The glandular stomach is the abomasums chamber in ruminants, which is the true stomach that secrets HCl, pepsin and other digestive enzymes.
(D, duodenum; O, oesophagus;CC, connecting chamber;
GS, glandular stomach; PB, parietal blind sac)
Although hippos have a ruminant-like digestion, they do not gain maximum benefit from this arrangement because they do not regurgitate the food. This makes hippos have a less sufficient digestive system that extract less nutrition from a leafy plant diet compared to a similarly-sized ruminant obtain from the same meal. Hippos overcome this by living a low energy expenditure lifestyle.
Evolutionary Summary of a Shark's Digestive System
The mouth and teeth directly show the feeding habit of sharks. Sharks do not chew food; the main function of oral cavity is to capture and hold food. Therefore, there is no secretion of digestive enzymes in this part.
Unlike the esophagus in mammals, the esophagus of sharks is short and wide, and there are no “demarcation zones” like the upper and lower esophageal sphincters. Esophagus is composed of striated muscles, and it can stretch during swallowing. There is no enzyme-producing gland in the mucus membrane in the esophagus, so the initial digestion of food takes place in stomach.
The food will enter the J-shaped stomach, which secrets gastric acid and pepsinogen to digest what is eaten. The stomach turns food into mush, which can be easily absorbed by the intestine. The pyloric valve controls the passage of the mush due to its small size. Although the intestine of sharks is short compared to herbivores’, it is effective at absorption due to its large surface area. The intestine of shark is composed of spiral valves, which increase the surface area of the intestine. Finally, the waste products enter the cloaca for excretion.
The mouth and teeth directly show the feeding habit of sharks. Sharks do not chew food; the main function of oral cavity is to capture and hold food. Therefore, there is no secretion of digestive enzymes in this part.
Unlike the esophagus in mammals, the esophagus of sharks is short and wide, and there are no “demarcation zones” like the upper and lower esophageal sphincters. Esophagus is composed of striated muscles, and it can stretch during swallowing. There is no enzyme-producing gland in the mucus membrane in the esophagus, so the initial digestion of food takes place in stomach.
The food will enter the J-shaped stomach, which secrets gastric acid and pepsinogen to digest what is eaten. The stomach turns food into mush, which can be easily absorbed by the intestine. The pyloric valve controls the passage of the mush due to its small size. Although the intestine of sharks is short compared to herbivores’, it is effective at absorption due to its large surface area. The intestine of shark is composed of spiral valves, which increase the surface area of the intestine. Finally, the waste products enter the cloaca for excretion.
Evolutionary Summary of a Tiger’s Digestive System
Historians believe that the first mammals emerged during the Jurassic period (Mesozoic Era. 190 million years ago) from small reptiles. At first they were very basic and their diet and digestive system were pretty similar to small dinosaurs. It was not until 5 million years ago that we could see "modern" mammals. With their emergence, the digestive system was modified depending on the animal's diet, dividing mammals in three big groups: carnivorous, herbivorous and omnivorous. Tiger belongs to the first group.
The most important facts we should know about Tiger's digestive system are:
- Carnivores have shorter digestive tracts that allow them to obtain nutrients from the meat they consume quickly. Their cecum is small due that their diet only consist of small amounts of plant material.
- A carnivore's teeth are long sharp and pointed. These are tools that are useful for the task of piercing into flesh.
- Carnivore saliva's does not contain digestive enzymes.
- Carnivores have greatly enlarged stomachs which encompass between 60 and 70 percent of their entire digestive tracts. Their stomach secretes powerful digestive enzymes with about 10 times the amount of hydrochloric acid than a human or herbivore. The pH is less than or equal to 1 with food in the stomach.
- A carnivore's or omnivore's small intestine is three to six times the length of its trunk. This is a tool designed for rapid elimination of food that rots quickly.
- Carnivore's liver is a tool designed with the capacity to eliminate ten times as much uric acid as the liver of a man or other plant eater.
Historians believe that the first mammals emerged during the Jurassic period (Mesozoic Era. 190 million years ago) from small reptiles. At first they were very basic and their diet and digestive system were pretty similar to small dinosaurs. It was not until 5 million years ago that we could see "modern" mammals. With their emergence, the digestive system was modified depending on the animal's diet, dividing mammals in three big groups: carnivorous, herbivorous and omnivorous. Tiger belongs to the first group.
The most important facts we should know about Tiger's digestive system are:
- Carnivores have shorter digestive tracts that allow them to obtain nutrients from the meat they consume quickly. Their cecum is small due that their diet only consist of small amounts of plant material.
- A carnivore's teeth are long sharp and pointed. These are tools that are useful for the task of piercing into flesh.
- Carnivore saliva's does not contain digestive enzymes.
- Carnivores have greatly enlarged stomachs which encompass between 60 and 70 percent of their entire digestive tracts. Their stomach secretes powerful digestive enzymes with about 10 times the amount of hydrochloric acid than a human or herbivore. The pH is less than or equal to 1 with food in the stomach.
- A carnivore's or omnivore's small intestine is three to six times the length of its trunk. This is a tool designed for rapid elimination of food that rots quickly.
- Carnivore's liver is a tool designed with the capacity to eliminate ten times as much uric acid as the liver of a man or other plant eater.