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Many people spend a third of their time consciously trying to control
how to get food into their digestive tracts and another third thinking about
how that food is doing when it gets into their digestive tracts and another
third of their time consciously trying to control how to get their food
intake out of their digestive tracts. However, once food is swallowed, the
conscious ability to control the passage of food is almost completely lost.
When the food reaches the point of elimination some conscious control is
again reestablished in the digestive system.
The gastrointestinal track or as people call it, the digestive system, has
the main purpose of break down food, both solid and fluid into sustenance
for the various tissues and systems in the body. A normal digestive tract
squeezes the utmost benefit from what it eats. Feces are the products left
over when the body has selected everything that is of use from the food
that has been eaten.
The digestive system distance ranges from the mouth to the bottom of the
trunk, which when we look at it, seems like no more than two or three feet,
but is really about 30 feet and like a railway station consisting of signals,
checkpoints, and control devices in a turning, zigzagging, coiling track
system.
From the moment the three main types of food-carbohydrates, fats and proteins-enter
the mouth, they are exposed to chemical and mechanical actions that begin
to break them apart so that they can be absorbed through the intestinal
walls into the circulatory system.
Stomach
About 10 inches down the esophagus, the swallowed food or bolus is now fairly well minced and turned into a pulpy mass as it passes into the stomach. The function of the stomach is best described as a food processing unit (similar to one you may have in your kitchen) and a storage cistern. It looks like a deflated balloon when empty, but when full, it becomes about a foot long and six inches wide able to hold about two quarts of food and drink. Persons have been known, however, to live a full life with part or even all of it removed. The stomach is both chemical and mechanical. Various chemicals in the stomach like the digestive enzymes pepsin, rennin, and lipase interact to break down the food. In addition, hydrochloric acid creates suitable environment for the enzymes and assists in the digestion. Also, watery mucus provide a protective lining for the muscular walls of the stomach so it will not be digested by the acid or enzymes. The mechanical action of the muscles in the stomach constrict and relax in a continuous motion blending, whipping, and stirring the stomach's contents into chyme, a pulpy substance that can be handled by the small intestine.
Back to the top.Small intestine
The small intestine is the longest organ of the digestive tract. It is divided up indiscriminately into three sections: the duodenum, the jejunum, and the ilium.
Duodenum
This is the place where the ultimate destruction of food digestion reaches its completion and where the acidity of chyme is nullified. The nutrients in the food eaten many hours ago have almost been diminished to molecules small enough to be absorbed through the intestinal walls into the bloodstream. Carbohydrates are diminished into simpler sugars; proteins to amino acids; and fats to fatty acids and glycerol. Enzymes are secreted by the walls of the duodenum and unite with the bile (essential for the digestion and absorption of tenacious fatty materials) and pancreatic enzymes in the duodenum.
Jejunum
Peristalsis pushes the nutrient liquid out of the duodenum into the first reaches of the jejunum. A greater number of villi , microscopic, hair like structures, begin to absorb amino acids , sugars, fatty acids and glycerol from the digested contents of the small intestine, and starts them on their way to other parts of the body. This part of the small intestine executes a digestive operation so that what is passed on to the large intestine is a thin watery substance almost completely devoid of nutrients.
Ilium
This is the place which is about a third of the small intestine. The greatest number of the estimated five or six million villi in the small intestine are found along the ilium making it the main absorption locale of the gastrointestinal tract. The villi here are always in a fretful movement: oscillating, pulsating, lengthening, shortening, growing narrower then wider, extorting every particle of nutrient.
Back to the top.The Liver, Gallbladder, and Pancreas
Legitimately, these three organs lie outside of the gastrointestinal tract. Nevertheless, digestive fluids from all three meet like intersections of a railway track at the common bile duct, and their movement from there into the duodenum is controlled by a sphincter muscle. The pancreas is a producer of digestive enzymes. The gallbladder is a small reservoir for bile. The liver reproduces nutrients so that they can be used for cell-rebuilding and energy.
Back to the top.Large Intestine
There is a merger between the illium and the cecum, the first section of the large intestine. Any solid substances that flow into the large intestine through the ileocecal valve (which prevents back flow into the small intestine) are as a rule indigestible, or are bile constituents. What the cecum primarily inherits is water.
What the large intestine essentially does, other than act as a passageway for removal of body wastes, is to act as a provisional reservoir for water. There are no villi in the large intestine and peristalsis is much less forceful than in the small intestine. As water is absorbed, the contents of the large intestine change from a watery liquid and are compressed into semisolid feces. Nerve endings in the large intestine signal the brain that it is time for a bowel movement. The fecal material moves through the colon down to several remaining inches known as the rectum and out through the anus an opening controlled by the outlet valves of the large intestine.
Back to the top.Enzymes
Site of Enzyme Origin Enzyme Nutrient It Breacks Down Product Of Enzyme Action Place of Enzyme Action Salivary Glands Salivary Almalase Carbohydrates-sugars Simple Sugars Mouth Gastric glands Pepsin Proteins Amino Acids Stomach Liver Bile Fats/Lipids Emulsifide Fats Small Intestine Samll Intestine Maltase, Lactase, Sucrase Carbohydrates Simple sugars Small Intestine Pancrease Trypsin, Lipase, Amylase Proteins, Fats/Lipids, Carbohydrates Amino acids, Glycerol/Fatty Acids, Simple Sugars Small Intestine
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Mechanical Digestion takes place in the mouth, where the the saliva, teeth, and tongue all play an important role in this digestive process.
Saliva
The smallest taste, smell, and anticipation of food sends signals to the brain. The brain in turn sends messages to a system of salivary glands. Saliva is essentially made up of water and begins to soften up the food so it can pass more smoothly down the throat. Besides water there is also a very special substance, an enzyme called pytalin , whose main task is to breakdown the food into simpler forms.
Teeth
The aftermath of the action of the teeth in digestion results in two outcomes: havoc and devastation. The teeth are gears to demolish chunks of food by a series of actions such as clamping, slashing, piercing, grinding and crushing.The teeth do the first drastic destruction to food in the digestive system.
Tongue
The tongue consists of four types of taste buds--salty, sweet, sour, and bitter--and is a very maneuverable and pliable arrangement of muscle. It helps to remove, and dislocate food particles in the teeth and shifts food around in the mouth in order to assist with the all important act of swallowing. The act of swallowing food, which at this place in the system is called a bolus, brings many organs into action. As the top of your tongue presses up against the hard palate , the roof of your mouth, food is shoved to the back of the mouth. This action in turn brings the soft palate and ursula (the place at the very back of the mouth where there is a teardrop shape located) into action. They keep the food from being misguided toward the nose. Once past the soft palate, the food is in the pharynx, a train station with two tracks, one leading to the trachea (windpipe), the other to the esophagus (food tube). The epiglottis projects out from the trachea side and helps to admit free movement of air as it is swallowed and at the same time restricts entrance to the esophagus. The larynx -hyper link, provides the epiglottis with most of its muscle for movement. It applies an upward force that helps to relax some tension on the esophagus, so that food enters where it is meant to go, down the esophagus and not down the windpipe. Many people have experienced at some time or another when the swallowing action did not go as it was supposed to.
Cough. Cough. Choke.
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This mechanical action has to do with sets of muscles that cooperate to move both liquid and solid food along the digestive tract. In other word, it pushes food along your esophagus, stomach, and intestine.. Gravitational pull is lessened in a sense when food enters the esophagus because of peristalsis. Peristalsis helps a person to swallow lying down or even standing on their head. Peristalsis has another essential task besides assisting in the movement of food through the body. It also helps to knead, agitate, and pound the solid residue that is left after the teeth or those without teeth, the gums, have done their best.
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The gastrointestinal tract is supplied with a number of muscular valves. These control and direct the quantity of food that goes through the digestive tract and inhibits the back movement of partially digested food.
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