Monday, March 30, 2009
Ruminating Monkeys :D
On page 113, Sean Carroll talks about special digestive system of Colubus monkey. Compare and contrast the digestive tract of colubus monkey and human. Describe different digestive enzymes of Colubus monkey and explain how digestion is regulated in both human and the Monkey. Also, what is the selective advantage of Colobus monkeys as leaf-eaters?
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The Colobus Monkeys have developed a four chambered stomach, as opposed to the human's one chamber stomach, which aides in the breakdown of nitrogen from plants. Humans, are not able to digest the cellulose that is found in plants; however, these ruminant monkeys, contain anaerobic bacteria which break apart the cellulose found in plant leaves. The monkeys, also like cows, regurgitate their food, so that they can break it down further and then send it back down to their stomach for even more further digestion.The fermentation of greens occurs in the Colobus Monkey's enlarged saccus gastricus, which is one of the four chambers of the stomach. This is a selective advantage for these monkeys because they are able to make use of a lot more nitrogen in their diets. But why is nitrogen important in one's diet? Well, the answer to that is the fact that one of the components to make DNA is nitrogen, and in order for an organism to replicate its DNA or RNA in cell division, it must have a sufficient amount of nitrogen.
ReplyDeleteAccording to Carroll, the colobus monkeys, in contrast to other primates, are leaf-eaters. The leaves they eat undergo the process of fermentation caused by bacteria that live in one of the chambers of the multi-chambered digestive tract of the colobus monkey. Colobus monkeys have unusual stomachs, which are similar to the digestive systems of cows. The important feature of a colobus' stomach is that it has three or four different regions. The upper "sacculated" regions are very large and are separated from the lower acid region. The sacculated stomach and the specialized bacterial microflora enables the monkeys to digest large volumes of leafy material. If the stomach was not as large as it is these monkeys would not be able to get ample nutrition from their food. Colobus monkeys always have a belly full of food which is in the process of being digested.
ReplyDeleteIn addition, Carroll states that the monkey extracts the nutrients from the leaves from enzymes, such as ribonuclease, which “harvest the large amounts of nitrogen in the RNA of the fermenting bacteria” (113). In contrast to humans, who do not employ ribonuclease as a major digestive enzyme, these monkeys have large amounts of this enzyme to facilitate digestion. As a result of their abnormal number of ribonucleases, these monkeys select food items that are rich in mineral nutrients and nitrogen and low in content of the general digestion-inhibitors, lignin and tannin.
The reason, according to Carroll, for such an anomaly is that instead of having one copy of the gene which makes the ribonuclease, this species has three copies of the gene. Some time during the evolution, it proved a selective advantage to duplicate the gene because of the eating habits of these animals. These copied genes, however, are not exact replicas of the original gene. They have acquired certain advantages along with their evolution. For example, because they teem in the acidic environment of the digestive tract, the proteins of the new genes live in optimal conditions of highly acidic environment.
In comparison to these monkeys, humans have a very small gut. This most likely is because the belly of a colobus monkey is always filled with the leaves it is digesting where as humans store the energy of food in things like fat reserves and glycogen in the liver; thus, we do not need such big guts to constantly store our food.
Most likely the colobus monkey relies heavily on leaves to constitute their diet in comparison to other primates because of their lack of thumbs. This proves a selective advantage for them because it enables them to quickly move through trees thus making it easy for them to find new reserves of food in their habitats and also to avoid predation.
In accordance with the theme of structure and function, the unique structure of the colobus’ tooth serves as a selective advantage to it in order to exploit its ecological niche. The bilophodont teeth of these animals serve as a pair of wedges bordered by blades that are adapted for processing young leaves and though seeds. Thus, although they lack thumbs, these monkeys can still take advantage of the resources in their environment because the morphology of their teeth exposes them to a wider range of leaves/food to eat from.
Because colobus eat leaves, which are low in nutritional value, they have to eat a lot more than humans, which can receive large amounts of nutrition from meats, vegetables, etc. Another contrast between humans and these monkeys related to digestion is the level of activity. Because of the aerobic processes of cellular respiration, the breakdown of foods to ATP is fast and efficient; anaerobic respiration only takes place during times such as extremely strenuous exercise. However, Colobus have long periods of inactivity possible related to the fermentation process, which is very slow compared to the process undergone by humans. Another side effect of this process is a build up of methane and carbon dioxide gases.
A similarity between a human’s and colobus’s process of digestion is that the stomach functions in protein digestion with some of the basic enzyme: pepsin. Similarly, digestion of lipids, like in humans, takes place in the small intestines. It is the digestion of carbohydrates that presents divergence.
The digestion of simple sugars like fructose and glucose is similar: they are readily absorbed by the body and are used directly along ordinary metabolic pathways. Disaccharides, such as sucrose or lactose, must be hydrolyzed into simple sugars in the small intestine before they can be absorbed and used, similar to how humans process lactose.
As Stacey already mentioned, one of the major differences between humans and Colobus monkeys is the ability to digest cellulose-essential for a leaf-based diet. The process begins the same with salivary amylase beginning the breakdown of carbs. The difference comes later. In primates, as in other plant-eating vertebrates, digestion of structural carbohydrates is carried out by symbiotic microorganisms that live in the digestive tracts of their hosts. In the process of fermentation, cellulolytic bacteria degrade the structural components of plant cell walls. As a byproduct of this activity, the bacteria release volatile fatty acids, (VFAs) also known as short-chain fatty acids. The host animal uses these acids, among them acetic, propionic, and butyric acid, as readily available energy in the bloodstream or, ultimately, glucose storing them in the liver. The evolution of this symbiotic relationship is essential because no vertebrae produce the cellulose-breaking down enzyme. As symbiotic bacteria die off, lysozymes (digestive enzymes) break down the bacterial cell walls, reducing the microbes to a form that is usable for protein.
Sources:
http://www.springerlink.com/content/c535662661884713/
http://www.anthropology.wisc.edu/lambert/pdf/Lambert1998.pdf
The human digestive system is fairly easy to follow. Food is taken in through the mouth where digestion begins. The teeth grind up the food which increases the surface area, making it easier for digestive enzymes to access the food and being breaking it down. Salivary amylases are released into the mouth from the salivary glands which begin breaking down carbohydrates. The food, now called a bolus, enters the pharynx which is a junction that opens up to the esophagus and the trachea. The epiglottis, a cartilaginous flap, covers the trachea and allows food to pass into the esophagus where peristalsis, or muscles waves, help to carry the bolus down into the stomach. The stomach releases gastric juice which helps to break down the extracellular matrix that binds cells in meat and plants together as well as kills off any potentially harmful bacteria. Another component of gastric juice is pepsin. Pepsin is an enzyme that breaks down proteins. The now partially digested food is referred to as acid chime. The acid chime then passes into the small intestine. Carbohydrate digestion that began in the mouth continues here with pancreatic amylases such as maltase and sucrose. Proteins are further digested by trypsin, chymotrypsin, aminopeptidase, carboxypeptidase, and dipepsidase. The digestion of DNA and RNA is facilitated by nucleases and fat is digested first by bile salts and then by lipase. After all of these enzymes have been activated and begin breaking down the food, the nutrients are absorbed through the wall of the small intestine and into the blood stream. Everything that is not absorbed is passed into the large intestine. It passes by the appendix which no longer serves a function in humans. While in the large intestine, much of the water is reabsorbed. The large intestine also contains the bacteria E. coli which generate gases and even produce vitamins which are absorbed by the human. At the end of the large intestine is the rectum. This is where the feces, what is left of the food, is stored until it is expelled from the body through the anus.
ReplyDeleteThe human digestive system is regulated by a few key hormones. Gastrin, one such hormone, is released by the stomach which stimulates the production of gastric juice in the stomach. Enterogastrones are group of hormones secreted by the small intestine. When chyme enters the small intestine, its acidic pH stimulates the release of secretin which signals the pancreas to secrete bicarbonate which neutralizes the acid in the chyme. Cholecystokinin (CCK) is released in response to the presence of amino or fatty acids. CCK triggers the release of bile from the gall bladder as well as the release of pancreatic enzymes.
One of the most obvious differences between the colobus monkeys and humans is that the monkeys have a three or four sectioned stomach. The upper regions are much larger than the lower acidic stomach. This upper stomach along with the presence of bacterial microflora enables the monkey to digest large volumes of food. Without this, the monkeys would not be able to extract enough nutrition from their food as the leaves are not highly nutritious and large volumes of them are required to sustain the monkeys. The enlarged upper portion of the stomach is referred to as the saccus gastricus and is the site of over half of the monkey’s digestive processes. The monkeys are continually digesting as their stomachs are always full of leaves. This would explain why the colobus’s digestive system is so much larger than that of humans and also explains why the monkeys always appear to have a pot-belly. Their food constitutes roughly a quarter of an adult’s body weight. The partially digested leaves are periodically regurgitated to the mouth so further chewing can occur before it is re-swallowed back to the stomach. Their stomachs contain specialized bacteria that help break down the leaves and also help to neutralize toxins that are common in the leaves. The monkeys maintain relatively constant temperature and level pH in their stomachs to facilitate the survival of these vital bacteria. Ribonuclease is an enzyme that is found in the colobus monkey that Carroll focuses on. The monkey contains three forms of the pancreatic enzymes as opposed to the single form in most other organisms including humans, which helps to, “harvest the large amounts of nitrogen in the RNA of the fermenting bacteria,” (Carroll, 113). Once the leaves have been digested enough, they pass into the small intestine. This step is very similar to that of a human as enzymes from the pancreas are released and continue digestion while the walls of the small intestine absorb any available nutrients. The large intestine, where the food goes next, also serves the same function in the monkeys as it does for humans. Water is reabsorbed by its walls before the remainder of unabsorbed material is passed out of the body through the anus.
The ability of the colobus monkey to digest these leaves is a huge selective advantage. The leaves are an extremely prevalent food supply and are not difficult to find. This means that the monkeys do not have to search very hard to find food and are therefore in no danger of starvation. Their extremely large digestive system allows them to continually digest food in order to absorb enough nutrients and the presence of specialized bacteria in their stomachs allow them to break down the cellulose in the leaves that they would be unable to do without the bacteria.
Sources:
http://www.zoo.org/factsheets/colobus/colobus.html
http://www.totallywild.net/press/index.php?p=press_item&id=365
http://edis.ifas.ufl.edu/DS061
http://resources.metapress.com/pdf-preview.axd?code=v20p251841850891&size=largest
The Colobus monkey has a special system of digestion that is unique to its self as a monkey and a primate. Like all old world monkeys it has the ability to have trichromatic vision, which allows it to see across the visible spectrum. This allows the Colobus monkeys to select the younger, juicier, and greener leaves that are very nutrient filled; they are able to detect them because the greener the leaf the younger and healthier. They also have something that not any other chimp or ape and only his close relative cousins posses. Colobus monkeys are ruminants. That means his diet can be mainly leaves because his stomach is larger than normal and contains four chambers. An adult monkey will consume four to six pounds of leaves a day. This four chambered stomach aides in the breakdown of nitrogen from plants, and they have the right enzymes to digest cellulose. But their has been a unique bacteria that has grown in their digestive tract; which helps digest the large bolus of leaves as it travels slowly from each chamber, and at the same time it travels slowly to get maximum efficiency. The products left over from the bacteria are essential nutrients that the monkeys need. To break it down, the Colobus monkeys have evolved to create unique enzymes that will break the nutrients down so they can be used by the monkey. The enzymes they use to get their energy are ribonuclease. A study of their digestive juices shows that they have large numbers of ribonuclease. This is why they eat a lot of leafy food because they are able to get the nitrogen out of the food. Carroll says this because they have three copies of the ribonuclease gene. Their complex stomach also lets them digest mature and or toxic foliage that other monkeys are not able to. The upper regions of the stomach are much larger than the lower regions. They are also very well separated because the lower region is much more acidic. The upper stomach and the specialized bacteria, microflora, is what enables it to take in large amounts of leafy material. Then the lower stomach is used to extract what the bacteria couldn’t by breaking it down as much as possible. These large stomachs are a necessity to their survival because leafs do not have that much nutrition, so they need large amounts of it to get ample food. They always have a belly full of food that is in the process of being digested. They spend much of their time eating. Once the leaves have been digested enough, they pass into the small intestine. This then becomes very similar to human digestion because many enzymes act upon the further breakdown and absorption of the food. There is a selective advantage to the monkeys having a large stomach and mainly leaf eaters. They live on top of the trees, where the most nutritious and healthiest leaves are found. However, they still feed on leaves that are not filling. Since they have large stomachs they are able to feed on many leaves to meet their energy demands. Also living on top of the trees, they are mainly by themselves, so they will have many young leaves. They will always have a constant food supply that will be there because; they are able to feed on leaves like no other monkey can.
ReplyDeleteThe human digestive system is very different from the Colobus monkey digestion. Humans like the monkeys have trichromatic full color vision. This is used to help find food quicker and led to the decline of our sense of hearing and smell. Unlike the monkey humans have one stomach, but are able to get larger amounts of energy and nutrients from their food because they are omnivores. This allows humans to eat green leafy food, as well as meat to meet all their energy demands. The human digestive system has a lot of mechanical digestion like chewing and the churning of the stomach. This is used to help let the chemical digestion to be as effective as possible. The chemical digestion begins in the mouth with salivary amylase breaking down the carbohydrates, and while the teeth chew it increases surface area to allow more of the amylase to reach all the carbs. Then the food bolus passes through the throat, down the esophagus and into the stomach. Then in the stomach the gastric juices, much like the acid in the Colobus monkey, help break down the proteins and make the fats in small molecules. The stomachs juices are a feedback relationship that starts producing the acid once it sense food in the mouth. Then pepsin is added to help break down the proteins. The acid does not do any of the digestion, it creates optimal conditions for the enzymes to work and it denatures the proteins. The largest process of the digestion occurs in the small intestine. In here all the smaller macromolecules are broken down even further, by the many enzymes and digestive juices created by the liver and pancreas. Bile emulsifies fat into small molecules that will later be absorbed by the villi. In here maltase, sucrase, and lactase each break down the sugars from specific things that were not able to be broken down by the salivary amylase. Trypsin, chymotrypsin, aminopeptidase, carboxypeptidase, and dipepsidase finish the job of pepsin and break down the protein and its peptide bonds. Then the fat molecules are further digested by lipase. The nucleaic acids found in the food are broken down by nucleases. This all happens in the upper part of the small intestine, and then it moves to the lower part of the intestine. Where villi and micro villi are used to absorb the nutrients into the blood stream. The nutrients not absorbed by the small intestine move to the large intestine which contains E. coli. The E. coli extracts some vitamins from the food and then the large intestine absorbs that and the left over water that wasn’t picked up by the small intestine. The waste is then excreted through the uranus. There are many more enzymes in a human digestive system, which is why we are able to eat both leafy food as well as meats. The only thing is that humans are not able to digest cellulose because they do not contain the right enzymes that break apart the chains in the cellulose. Also because the human digestive system is more advance, humans are able to eat and go long periods of time between eating. This is because we are more efficient at getting nutrients in our diet; as well as a balanced diet that provides us with food with higher caloric intake. Unlike the Colobus monkey, humans don’t have a full stomach all the time, so this regulation happens with hormones. When we see, smell, or taste food, impulses from the brain to the stomach initiate the secretions of gastrin. This then stimulates the release the of gastric juice. This starts with a large amount of gastrin and then recycles during the meal and has a constant amount gastrin to be released. The small intestine has its own hormones, secretin and cholecystokinin (CCK). These two hormones together are caller enterogastrones. The pH of the acidic chyme stimulates the release of secretin, which tells the pancreas to release bicarbonate to neutralize the pH of the chyme. CCK is stimulated by the fatty acids in the chyme and tells the gallbladder to release bile to start the emulsification of the fatty acids.
http://itech.fgcu.edu/faculty/sstans/ColoHuff.html
http://www.zoo.org/factsheets/colobus/colobus.html
AP bio book