Break Down The Food You Eat Biology Essay


When you crunch into that bright red, delicious apple, do you ever wonder what actually happens after you swallow it? You've often learned that bread, fruit, and vegetables are good for you, while fats and sugars are bad, but did you ever wonder why? The digestive system inside your body is somewhat of a medical marvel. The entire system is designed to break down the food you eat into tiny bits of matter called molecules that can be absorbed into your blood to be taken where they are needed. This paper will detail how the digestive system works, as well as various malfunctions that could occur.

The digestive system is the only major body system that has one entrance into and one exit out of your body. Initially, the food is not in a form your body can use. When you first swallow your mouthful of food, it does not benefit your body at all. Therefore, your body must first break it down and turn it into something your body can use more effectively. Your body cannot produce all the nutrients it needs by itself, so it must process nutrients from the outside world. In essence, this is why your digestive system exists.

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Digestion is best defined as: "The process by which food and drink are broken down into their smallest parts so the body can use them to build and nourish cells, and to provide energy" (C). The digestive system contains the most individual organs that contribute to the overall system. Aside from the circulatory system which benefits all organs in the body, the first organ in this system is the mouth, which contains the tongue, teeth, and salivary glands. The first step in digestion is the first bite into whatever food you put into your mouth. Teeth are specifically shaped for different functions: incisors, which are right at the front of your mouth, are meant to slice the food into bite-size portions that your mouth can actually handle. One pair of canines behind the incisors are used to help tear the food apart and help both the incisors and molars do their jobs. Behind the canines, three pairs of molars then crush and mash the mass of food, turning it into a mush that your body can digest. A second step of digestion in the mouth is the saliva it produces. Saliva is a weak digestive enzyme

glands in your mouth produce to help break down the food. With your teeth mashing food into tiny little bits, the saliva then covers a greater surface area of the food, and breaking it down chemically. Also a digestive organ, the tongue rolls around the mass of food and, along with the saliva, and turns the blob into a sticky bolus which is easy to swallow. This is the one step of digestion you somewhat control, and your body takes digestion over from here.

The second step of digestion, which accomplishes very little, is swallowing. Swallowing is a complicated series of muscle contractions, which involves blocking off both your nasal passages and your trachea, which leads to your lungs. The tongue then "rolls" the bolus into your pharynx, and it finally leads into your esophagus. Coated with mucous, the esophagus is a hollow tube of muscular tissue. The food is pulled through the esophagus to the stomach by a muscular motion called peristalsis. No digestion happens inside the esophagus; the food is merely transported. At the end of the esophagus is a circular muscular mass called a sphincter. This mass seals off the connection between the esophagus and the stomach, but opens up to let boli of food through.

The next organ in the digestive tract is the stomach, a J-shaped organ that can hold up to one litre of matter at one time. This is not necessarily the maximum capacity, but any more than this can be harmful to stomach tissue. The tissue of the stomach is thicker and more muscular than the esophagus. Inside is a very thick lining of mucus to protect the stomach from digestive juices. The juices inside the stomach are actually a powerful acid, with a pH of about 2, approximately the same as battery acid. When the stomach has food inside it, the muscular tissue begins to move in a way as to "churn" the food inside. While the stomach is churning, the food is bathed in these digestive juices, and major chemical breakdown begins here, mostly of proteins.

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The last step of digestion occurs in the small intestines. This long, tubular organ is tightly coiled up inside your abdomen, and this is where absorption of nutrients occurs. By now, most of the food is broken down into molecules that can actually be used by your body. The digested food leaves


your stomach via a second sphincter in a form called chyme. Chyme is a thick, black liquid that enters your intestines to be absorbed into your body. At the very beginning of the small intestines is a section called the duodenum. This section receives digestive enzymes from the liver, gallbladder, and pancreas. The liver secretes bile salts that both breaks down fatty materials into something the intestines can absorb, and increases the pH of the chyme so that the intestines aren't burned or damaged. Being mostly a storage tank, the gallbladder secretes a minor amount of insulin to manage the amount of sugar that enters the blood, and stores the bile that the liver makes until it is needed. The gallbladder is, in a way, a non-essential organ because its job can be taken over by the liver. However, without it, the liver can be overworked. The pancreas secretes an enzyme to break down carbohydrates into their basic molecules so they can be absorbed. All these secretions are introduced to the chyme in the duodenum.

The broken down chyme is then pushed through the intestines by peristalsis. The journey through the intestines is a very long one, because the intestines are filled with little hairs, called villi, that aid in absorption. Villi then sweep the chyme as it goes by, and begins to pull off molecules, which are directed to a blood capillary to be used in the body. Covered in microvilli which absorb the food molecules, the surface area of the intestines is increased by these two things.

Some types of food cannot be used by your body at all. You may have heard that fibre "cleans you out." This is literally true, because fiber breaks down very little inside your body. The fiber is swept along with the rest of the food you eat, and pulls all the waste material out of your intestinal tract. As well, the body doesn't absorb everything, and some waste is created. Instead of leaving it inside your intestines to rot and make you sick, you eat fiber to move this waste out of your body. This is where the colon is involved. The colon, or large intestines, is slightly larger in diameter than the small intestines, and has no microvilli. The purpose of the colon is to transport waste to a body exit.

The colon also moves the food by peristalsis, and it wraps around the small intestine bundle from the


right side of your abdomen around the top - underneath your liver and stomach - down the left side,

and finally around the bottom for a short distance. The waste, or fecal matter, gathers here to be expelled out the anus in a bowel movement.

The digestive system secretes liquids, called enzymes. These enzymes are designed to break down food in certain parts of the body. Each organ secretes its own enzymes to aid in digestion of the food, and each of these enzymes is necessary for complete digestion.

The first digestive enzyme to break down food is in the saliva in your mouth. This enzyme, called salivary amylase, is a very weak acid that aids in turning chewed food into a bolus that can be swallowed. This amylase primarily attacks starch in foods to turn it into maltose, which will be further digested inside the body.

Once food enters the stomach, gastric juices then chemically breaks down the bolus of food into the chyme mentioned earlier. One enzyme in these gastric juices is pepsin, produced to primarily target any protein inside the stomach. Pepsin is highly acidic, and breaks down the protein into peptides which can then be mixed into the chyme to be further digested in the intestines.

The pancreas is greatly involved in secreting enzymes to break down nutrients. To break down sugars into glucose and fructose for absorption in the intestines, the pancreas secretes pancreatic amylase. The pancreas also secretes trypsin, which plays a minor role in the digestion of protein. Additionally, the pancreas secretes an enzyme called nuclease, which breaks down any DNA and RNA found in the food into nucleotides. Nuclease digestion is digestion that occurs on a microscopic scale. This digestion is minute because this is literally involving digestion of protein cells, which are extremely small. The final enzyme the pancreas excretes is nucleosidases. This enzyme further breaks down the nucleotides into nucleic bases, sugar, and phosphate. These are then re-arranged to form ATP for the body to use. ATP is a small molecular structure that provides energy for the body which it both uses in bulk and recycles several times over.

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The liver also produces a digestive enzyme to use in digestion. The liver secretes bile salts,

which break down fat into fatty acids and cholesterol. These salts travel through the liver to the gallbladder, which then passes them on to the common bile duct where it is brought to the intestines.

The real molecullar digestion occurs inside the small intestines. Aside from being the collection point for all the digestive enzymes from the other organs, the intestinal tract also produces its own enzymes to aid in molecullar digestion. The first enzyme that the intestines produce is maltase. This enzyme attacks any maltose molecules in the chyme, breaking it down into glucose which can be absorbed into the blood. Another enzyme produced in the intestines is peptidases. This enzyme breaks down peptides from the stomach into amino acids, which can be used in the body. After all these enzymes have been introduced to the chyme, the bloodstream can absorb these nutrients, and distribute them to wherever they are needed in the body.

Not all enzymes related to the digestive tract are merely used for digesion, however. Several enzymes exist in other parts of the body, which we call hormone regulators. These hormone regulators aid in other things digestion-related, such as regulating blood flow, appetite, and many other things. The first hormone is gastrin. When activated, this hormone, tells the stomach to begin producing digestive juices to begin the digestive process in the stomach. Gastrin also plays a prominent role in skin-cell and mucosa production in the stomach and intestines.

The next regulator in the body is secretin. This enzyme causes the pancreas to produce a bicarbonate enzyme, which helps neutralize the chyme. due to the low pH of the chyme, a deficiency in this enzyme could cause extreme damage in the small intestines. Secretin also stimulates the stomach to produce pepsin while digesting to begin breaking down proteins. This enzyme also causes the liver to excrete bile salts into the digestive tract to break down fats.

A third hormone regulator is called cholecytokinin (CCK). CCK primarily manages the pancreas, telling it when to produce its digestive juices to break down carbohydrates in the intestines.


When old cells start to become damaged CCK also stimulates cell growth in the pancreas. A third thing

CCK manages inside the body is stimulating the gallbladder to empty, which sends bile salts through the common bile duct to the intestines. In this way, the enzymes CCK and secretin walk hand-in-hand to digest certain nutrients in the body.

Two different hormones control appetite. The first hormone, ghrelin, is produced in the stomach and small intestines in the absence of food. This hormone stimulates what we know as appetite. If we haven't eaten for too long, this hormone makes us hungry. Once we have eaten, a second hormone, peptide YY is produced, which neutralizes the ghrelin in our system, subduing our hunger.

The digestive tract provides nutrients and energy vital to our survival. The tract breaks down the nutrients: carbohydrates, protein, fats, vitamins, water, salt, and fiber. The exceptions to this are that salt and water are mostly processed in the urinary tract, although they still pass through part of the digestive tract. All forms of nutrition are digested by being chewed in the mouth and being broken down to the molecular level inside the stomach. The following descriptions offer details on the various nutrients your body breaks down.

Carbohydrates are useful to our system because, in short, they provide sugar and energy for our body. There are several types of carbohydrates, but ultimately they break down into two simple carbs, sugar and starch.

The digestible carbohydrates-starch and sugar-are broken into simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining of the small intestine. Starch is digested in two steps. First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose. Then an enzyme in the lining of the small intestine splits the maltose into glucose molecules that can be absorbed into the

blood. Glucose is carried through the bloodstream to the liver, where it is stored or used


to provide energy for the work of the body. (C)

in one simple step, sugars are digested and absorbed into the body. The digestion of sucrose (table sugar) is broken down into glucose and fructose by an enzyme lining the small intestine. The lining of the intestine absorbs these two molecules, and transmits them to the bloodstream for transport, use, and storage.

Proteins are needed in our body for building and repairing tissues of the body on a cellular level. Obviously using a chunk of steak or a peanut as a band-aid to heal a cut won't work, so the food has to be broken down first. Protein is one of the most dense digestible foods you can ingest, and requires significant effort on your body's part to break it down. Pepsin, an enzyme in the stomach, combined with extremely acidic gastric juices, begins the breaking down of protein. The broken-down protein then enters the small intestine to be further digested and absorbed. Both pancreatic enzymes and the intestinal lining break down the protein molecules into amino acids. The amino acids are then absorbed into the blood to begin repairing and strenghtening body cells.

Fats are a far more dense source of energy for the body. When the body is starving, fat can also help in producing a fine balance of body insulation and can be a reserve source of energy. Fat has a unique digestive process, because the stomach can't really digest fats. Almost all digestion of fat is done in the intestines. Bile salts secreted from the liver are channeled to the small intestines via the common bile duct. These salts break down fat into molecules of fatty acids and cholesterol. The fat is absorbed through the intestinal wall to provide energy for the body, and excess fat is sent to storage receptors throughout the body.

Vitamins are another essential nutrient that must be brought from outside the body. These are mostly digested in the form of fruits and vegetables, although other vitamins come from different sources.

Another vital part of food that is absorbed through the small intestine are vitamins. The


two types of vitamins are classified by the fluid in which they can be dissolved: water-

soluble vitamins (all the B vitamins and vitamin C) and fat-soluble vitamins (vitamins A, D, E, and K). Fat-soluble vitamins are stored in the liver and fatty tissue of the body, whereas water-soluble vitamins are not easily stored and excess amounts are flushed out in the urine. (C)

Fiber plays a unique role in the body. The body has no way to clean out waste in the digestive tract. If this waste material is left inside the body, it will eventually rot and begin damaging the intestinal tissue, basically acting as involuntary food poisoning. Therefore, this rotting food must be removed from the body in some fashion. Hence, we digest fiber. Fiber is literally undigestible in the body, and it passes through the system as a large bolus of waste. This can be moved with the peristalsis in your intestines, and will collect all the waste inside your tract. Before doing any damage, this can then be expelled from the body.

Water and salt play very minor roles in the digestive system. Some water is needed to avoid constipation in the colon. Salts are needed to keep diarrhea from occurring in the colon. As a source of sodium, salts are beneficial to the circulatory system.

The digestive system does wonderful things for our body. This system breaks down and absorbs vital nutrients that our body is missing, and it also expels waste from our body. Both of these functions are invaluable. Unfortunately, if we eat an unbalanced diet consistantly, or accidentally ingest toxic substances, serious damage to these organs can occur. The major disease that will be covered is an overview of hepatitis.

The inflaming of the liver is called hepatitis. Hepatitis can be transmitted by viruses, but it can also be contracted by ingesting too much alcohol, drugs, or other toxic subtances. The disease itself is not very deadly, but the complications of hepatitis can be lethal. Some complications include cirrhosis, in which the liver becomes severely scarred and is unable to regenerate anymore. If left untreated long


enough, hepatitis can evenually cause total liver failure, which is usually fatal.

Currently there are six classifications of hepatitis: Hepatitis A, B, C, D, E, and F. All these classifications mean that the liver was infected in a different way, and your outlook and treatment will differ between types of hepatitis. 90% or more of known hepatitis cases are either Hepatitis A, B, or C, which are all viral. This means that it is transmitted in the form of a virus that attacks the liver and body tissues. There are two classifications of viral hepatitis; you will either get acute hepatitis or chronic hepatitis. Acute hepatitis is when the illness will be temporary, so you will feel sick for a few weeks, possibly a month, but then your body will recover. Chronic hepatits is far worse. You can be fairly sure you have chronic hepatitis if you have been sick for six months or more, this means the illness will stay with you for a long time, and more aggressive treatments must be used. Chronic hepatitis is also contagious, and may reappear after years of being dormant. From this perspective, chronic hepatitis is serious.

Both Hepatitis A and E measure quite low on the severity scale. They are acute versions of the virus, and are contracted through handling fecal matter, ingesting water with sewage or other contaminants in it, or through ingesting contaminated food. Hepatitis A and E cannot lead to chronic illness, so this classification of hepatitis is very easy to avoid.

Hepatitis B is the most common classification of hepatitis to contract. As it can be spread very easily. This can be spread from mother to infant, and is spread through any form of fluid transfer: sexual contact, handling contaminated blood, etc... People with HIV are extremely likely to contract chronic Hepatitis B, and Hepatitis B does far more damage in a person infected with HIV. This disease is more significant than Hepatitis A or E, but is still curable, as long as it isnt left long enough to become a chronic disease.

Hepatitis C is known as the worst infection you can get, and is spread by directly contacting infected blood, usually by sharing drug needles or other injection tools. A small percentage of people


have managed to spread this infection through sexual contact, although this method of transfer is very

rare. Up to eighty-five percent of people with Hepatitis C will contract chronic hepatitis. Hepatitis C is very bad because it can lie dormant up to fifty years before making its presence known. This can result in serious liver damage because the infection was left untreated for so long.

Hepatitis D is mostly a complication of Hepatitis B. The only difference between the two is that the symptoms of Hepatitis D are visibly worse than in type B. The cure and complication risks are the same, just with worse symptoms.

Currently, there are no medical cures for Hepatitis A or E, but the body's immune system is more than capable of defeating this disease within a few weeks. A select few drugs used to cure HIV can also help to cure Hepatitis B and D. More drugs are being approved for use to make the curing of Hepatitis B and C a much easier process.

There are several easy methods of protecting yourself from any form of hepatitis. The most obvious is to just stay clean and avoid contact with blood or used needles, because blood-to-blood transfer is the most common method of infection. You can honestly never know if somebody is infected with hepatitis, so it is far better to just stay safe. Also, do your best to know where your water or food is coming from, as contaminated food or water can very easily transfer the disease. Condoms can be used to avoid contracting hepatitis through sexual contact, although this is not 100% foolproof. Vaccines can be taken to resist contracting Hepatitis A, B, and C. Although other medical conditions may prevent you from getting these vaccines, it is a good idea to get them, as they can cure hepatitis if you get the vaccine quickly after exposure.

The digestive system is truly a wonder inside your body. This system acts as the provider of

nutrients your body needs, and is vital to your survival. If your body did not have a digestive system, you would die within a few weeks, due to a total lack of nutrition. Nutrition is what keeps your body going, as well as providing energy and materials for your cells to repair themselves. Without these two


vital things inside you, your body would begin to fall apart, and you would be constantly tired. It is

also vital that you protect this system, as the malfunctions that can occur in the system due to improper care can be lethal. Hepatitis is only a disease of the liver. Each organ in the digestive tract can contract its own lethal diseases, many of which are more deadly than, or as deadly as hepatitis. Heed the warning, and take care of your digestive system; you are going to need it for a long, long time.