Internal Structural Adaptations Essay, Research Paper

1. In order to grow and survive an organism must metabolize. In order to metabolize, an organism must have access to nutrients and O2 at the cellular level. Within the kingdom Animalia, there are several solutions to the problem of delivery of said nutrients and O2.

Discuss, in a written format, the various internal structural adaptations (their form and function) associated with each of the four heart configurations discussed in class which facilitate the delivery of nutrients starting at the mouth and ending with the diffusion of particles into the cells.

Use diagrams, flow charts and specific examples as appropriate.

Cite your references.

Due: Tuesday, December 2nd

I will begin this essay by discussing the various internal structures of animals which possess a four chambered heart. Generally, these animals are more complicated and larger than those whose hearts have three or less chambers. I shall begin by discussing the actual heart, a sort of pump which is used to drive blood throughout the body.

The four-chambered heart, which is shared by most mammals, birds and some of the larger reptiles is the most complicated and the most efficient heart configuration in known existence. Blood which the body has depleted of oxygen enters the heart in one of two ways ? either through the superior vena cava, which comes from above the heart, or the inferior vena cava, which comes from below the heart. No matter which of the cavae the blood came from, it next enters the right atrium (or the right auricle). Blood from the right atrium slowly drains down into the right ventricle below it via the tricuspid valve ? when the right ventricle is finally full of all the blood it can contain, the valve closes shut, allowing no more to enter from the atrium. The blood-full ventricle suddenly and powerfully contracts, shooting the O2-delpleted blood up through the pulmonary valve, through the pulmonary artery and into the lungs. Oxygen contained within the lungs? alveoli diffuses into the blood, CO2 that the blood picked up in the body diffuses into the alveoli, and the blood then re-enters the heart via the pulmonary veins. The pulmonary veins drain into the left atrium of the heart which then, in a manner similar to that of the right atrium, drains through the mitral valve into the left ventricle. When it is full of blood, the valve shuts and the left ventricle contracts once more, shooting the blood out to the body via the aorta. Oxygen-rich blood travels through the body in various different arteries (the ?pulse? that you feel is from the blood-filled arteries moving and carrying your blood ? a common misconception is that pulse is felt in your veins). These arteries continue to branch into smaller and smaller arteries throughout your body until they become known as capillaries. Since capillaries are so small the walls which contain the blood within them are very thin ? so thin that the blood can almost come in contact with the various tissues of the body. When this occurs, the nutrients and oxygen from the blood diffuse across into the cells of the tissues, and the waste products from the cells of the tissues diffuse across into the blood. This new blood, devoid of O2 and carrying only waste, travels through more capillaries which slowly branch together forming larger capillaries and eventually forming veins. Veins, carrying their O2-malnourished blood, travel back into the heart where the blood collects new O2 and deposits its old wastes. And the process repeats once more.

Much like their hearts, the lungs of those animals with four-chambered hearts are far more complicated and efficient than those of any others. The purpose of the lungs and their surrounding respiratory systems is twofold: firstly, they collect oxygen which then diffuses into the blood and is passed on to various body cells and secondly they collect CO2 and other wasteful gasses from the blood and vacate them from the body. The process by which air enters the lungs is known as inspiration. Inspiration occurs when the muscles in the rib cage contract, forcing the ribs to lift themselves upwards. This in turn causes the entire chest cavity, including the lungs, to expand ? this expansion, in turn, causes the lungs to have a lower air pressure than their outside surroundings ? air, in turn, must rush into the vacuum-like lungs, balancing the pressures out (approx. ? litre of air enters the body with every breath). Air enters the lungs via a long sequence of tubes and passageways. From the external nostrils or mouth, it travels down the throat, past the larynx and into the trachea. The trachea eventually branches into two bronchial tubes, the right and the left, which each lead to a different lung. Within the lungs, the bronchial tubes continue to break down, fractal-like, into smaller and smaller parts. First they become the bronchioles, next they become the alveolar ducts and finally these tubes terminate with small, grape-like clusters of alveoli. Although the alveoli themselves are small, as a whole they certainly are not ? the surface area of these air sacs is about 50 times larger than the surface area of the skin).

It is within the alveoli that the important process of respiration takes place. Every cluster of alveoli is surrounded by capillaries coming from the left ventricle of the heart, full of O2-depleted and CO2-containing blood. Oxygen from the alveoli diffuses across the membrane into the blood, and CO2 from the blood diffuses across into the alveoli (remember this?) ? thus, the hearts and the lungs do truly work in unison. The air in the lungs now has lost some of its oxygen and is full of a little more CO2 (air entering the lungs contains approximately 21% O2 and 0.04% CO2 ? when leaving, it contains 14% O2 and 4.4% CO2), and must be expelled from the body. This process of ?expulsion? is known as expiration. It works much like the opposite of inspiration ? the muscles of the ribcage contract, forcing the lungs to do so as well. This contraction forces the air out of the lungs, and out of the body.

The process by which life-forms with four-chambered hearts acquire their O2 has now been described ? we have yet to learn about how they get their nutrients, however. Nutrients nearly always come in the form of food for nearly all members of the kingdom Animalia, and those with four-chambered hearts are certainly no exception. Food, after being attained in a variety of ways which do not need explanation, is inserted into the mouth. The mouth is lined with teeth which chew the food in a process known as mechanical digestion (simplifying the chemical digestion that shall be occurring further down the digestive tract), and possesses six different salivary glands which help break down starches within the food and lubricate the esophagus. From the mouth, food proceeds down the esophagus and into the stomach. The stomach is filled with various agents ? specifically, hydrochloric acid and three different enzymes responsible for breaking down different things (pepsin, rennin and lipase) ? all of these work on the food, breaking it down into smaller and simpler parts. When the stomach has at last done its part, it slowly releases its contents into the small intestine where the last steps of digestion shall take place. Here, as well as being hydrolyzed, predigested food is subjected to even more chemicals ? pancreatic fluids (which break down proteins into smaller, simpler parts), intestinal juices (which completes the process the pancreatic fluid began), and bile (which breaks down fats). Finally, material left undigested is solidified and moved into the large intestine (where, ultimately, it shall be removed from the body via the colon), whereas the useful materials are taken into the blood in a variety of ways.

The walls of the small intestine are lined with small villi which jet out of the sides. The major purpose of villi is to increase the surface area of the small intestine to allow for nutrients to be taken and transported throughout the body in a more effective and efficient manner. Water-soluble materials (carbohydrates, minerals, amino acids, et cetera) from the food are diffused directly through the intestinal wall to the arteries within the villi, from where they are transported up to the liver for refining and to the rest of the body within the bloodstream to use as fuel. Some other substances such as fats are diffused into the lymph vessels which are within the villi as well ? these vessels bypass the liver and deposit the nutrients directly into the blood flow.

In many ways, organisms with hearts of the three-chambered variety are very similar to those with four. Three-chambered animals include reptiles (as shown above) and amphibians ? in fact, the only reptiles whose hearts are not three-chambered are the crocodilians (which makes the above diagram not as effective as it ought to be). In many ways, three-chambered hearts are like their four-chambered counterparts. The blood enters the heart from one of the two cavae, proceeds into the left atrium, from where it drains down into the one ventricle (note the difference ? there are two ventricles in four-chambered hearts) until the ventricle is full. The ventricle then contracts, shooting the blood upward into the lungs (which are exactly the same as human lungs in both form and function). In the lungs, the blood, (within its capillaries), comes in contact with the alveoli where an exchange of gasses takes place (as I said before, the blood gives the alveoli its CO2 and takes the alveoli?s O2 ? not too fair a trade, I must say), before the blood proceeds back down into the heart?s right atrium. From there, the blood is pumped directly out of the atrium into the body (another difference between mammals/birds and reptiles), and the blood proceeds about its business in the usual, mammalian way ? it travels down arteries, eventually reaching capillaries and eventually exchanging its nutrients and gasses with the cells it contacts. Simple enough? The one reptile that is exceedingly different from the human in terms of heart form it the snake ? as well as its main heart, it has many smaller hearts along the length of its body to help push the blood along ? but lets not get into that at this time.

Reptiles and amphibians are remarkably similar to humans in terms of internal organs (which explains why frogs are so often dissected ? they can teach us about ourselves). I have already gone over the heart, now let us move on to the reptilian lung. I am glad that I have already explained the lungs of the mammals because, in essence, the reptilian lung works in exactly the same way (it expands thanks to the chest cavity, the air rushes in, goes all the way to the alveoli where the O2 is collected by the blood) ? I see no need to talk about it any longer, because it would just be wasting time ? re-read page 2 if you must, for more information. Much like their lungs, the digestive systems of reptiles are very similar to the mammals as well (perhaps because of the common ancestors they share). As with the four-chambered organisms, food enters at the mouth, is digested mechanically, proceeds down the esophagus into the stomach where it is subjected to various chemicals, enters the small intestine where more chemicals get their chance to break down the nutrients. Finally, lymph vessels and capillaries within the villi have the nutrients from the food diffused into them, and it is carried to the rest of the body ? yet again, read all about the digestive system of creatures with four-chambered hearts for more details.

Now we move on from the three-chambered reptiles to the two-chambered fish. The hearts of fish are far simpler than those of the creatures that have already been described ? they are simple, two-chambered organs. De-oxygenated blood from the body travels to the heart via one long vein (unlike the two in reptiles, mammals and birds) and is emptied into the fish?s left atrium. Once the left atrium is full, it pushes the blood up to the gills (which I shall explain in due time), the blood acquires its O2 and deposits of its CO2 in a manner not unlike that which has been described twice before, and flows back down into right atrium. From the right atrium of the heart, the blood is first transported into the head and from there all the way down a large artery to the rest of the body ? and voila? we have circulation. Just as the circulatory system is not too different from that of the animals which have been previously dwelled upon, the digestive system is similar as well. Fish ingest food through the mouth, mechanically digest it with their teeth (which can be either sharp or crushing), pass it through the esophagus to the stomach, subject it to all sorts of acids and dissolving juices, pass it from the stomach to the small intestine, break it down even more, and diffuse it into the surrounding villi. The wasteful undissolved products are expelled from the body via the anal vent which, basically, is like a human colon but in fish. For more information on how the nutrients are broken down and transported from the small intestine into the body, consult the earlier digestion sections.

As you may already know, fish spend most of their time underwater (yes, there are lungfish, but I won?t even begin to deal with those?) and thus must have special adaptations to allow for proper respiration. More often than not, these adaptations come in the form of gills. To supply themselves with O2, fish take a gulp of water and then expel it through the gill chambers which are located on either side of the head. The gill chambers are filled with gills which, basically, are small filaments made of flesh, covered in lamella (the main purpose of which is to increase surface area). When the water passes through the two gill chambers, the O2 in the water diffuses into the capillaries located in the lamella which then carry it down to the heart and allow the O2-rich blood to be pumped throughout the body, and the CO2 in the blood diffuses into the water. All in all, although fish use an unconventional, non-lunged method of respiration, they still gather the O2 for their blood in practically the same way and use it for exactly the same purpose ? to fuel the cells and allow for metabolism.

We now move on to the final heart configuration, the one-chambered heart. This type of heart is the simplest and least efficient of all, but exists in the most successful of all creatures, the insects and annelids. Perhaps complexity does not necessarily mean success. The heart of an insect is simply a long tube with openings on either end. Since an insect?s entire body cavity is filled with blood, the insect?s heart need only to contract and the blood within this cavity ?swishes around?, coming in contact and sharing its nutrients and O2 with all of the insect?s internal organs.

Since an insect does not have a conventional heart that moves the blood to the appropriate place to get oxygen, the body of the insect had to compensate. Although there are some exceptions (there are some that breathe through the skin and some that have gill-like structures), most insects ?breathe? through a series of 20 small holes on their sides known as spiracles. Upon entering a spiracle, air travels through a web of small tubes called trachea until eventually reaching the tracheoles at the end. These tracheoles function much like simpler versions of the alveoli which can be found in the mammalian/avian/reptilian lungs. Upon coming in contact with these tracheoles, blood in the body cavity collects O2 and deposits CO2 via the process of diffusion.

Finally, the most complicated system in the insect is probably the digestive system. The digestive tract of an insect begins, like most other creatures, with the mouth ? an insect uses its mandibles, which are a sort of set of jaws, to crush and mechanically digest their food. Once this process is finally over and done with, the maxillae (another sub-set of jaws) push the food down the bugs throat and into the second section of the digestive system, the foregut. Within the foregut, the chewed food first enters the crop, which is basically a place where the insect stores its food until it feels that the time for digestion is nigh. When it is ready to digest, the food moves from the crop to the gizzard ? a powerful, muscular chamber that moves around, crushing the food with its walls like a trash compactor and exposing it to salivary secretions all the way. Eventually, when the food?s treatment in the gizzard is complete, it moves on to the midgut. An insect?s midgut is like a human?s small intestine ? here, the food is finally broken down into its simplest components by a variety of chemicals and, when the time is nigh, it diffuses across the wall of the midgut into the surrounding blood ? voila, nutrients to supply to all the body?s cells. Waste matter is passed into the hindgut (the equivalent of the large intestine) in one of two ways ? firstly, and most conventionally, it can move from the midgut directly to its final resting place. Secondly, attached to the hindgut are a series of tube-like protrusions known as Malphigian tubules, which stick out into the blood-filled body cavity. When blood with waste nutrients comes in contact with these tubules, the waste diffuses into them and travels down into the hindgut, awaiting its ultimate excretion.

Although all animals may have different internal structures for doing it, they all perform the same purpose in nearly the same way ? they provide their cells with nutrients and oxygen. By observing the similar manners in which all animals collect and dispense nutrients and O2, you can see several common links between all the species, and by observing the far-more-than-coincidental way all the organs within any animal work in unison to keep the creature alive, you can gain a true appreciation for the living world.