Human Digestive SystemDigestion is the breaking down of food in the body, into a form that can be absorbed and used orexcreted. It is also the process by which the body breaks down food into smaller components that can beabsorbed by the blood stream.Human Digestive System -The Mouth + SalivaThe human digestive system is a complicated and impressive system. Understandinghow the digestive system works helps us to eat healthier. Stay healthy by what youeat and keep your digestive system healthy.When you eat food, the saliva mixes with the food. This is a very important processin preparing the food for the stomach. The salivary juices and enzymes help breakdown the food beginning the process of changing the food to the parts the body canutilize –such as carbohydrates (disaccharides –maltose, etc), proteins, fats,vitamins, minerals, etc.Breakdown of NutrientsWhen you take smaller bites and chew the food well before you swallow it, you helpmake the job of the stomach a little less difficult. The stomach is an amazing placewhere acids and enzymes work hard to kill bacteria, start the process of breakingfood down into small molecules -nutrients the body can actually process –such ascarbohydrates, fats, proteins, vitamins, etc.
The stomach’s digestive juices include saliva, mucous, hydrochloric acid (HCl),enzymes, bicarbonate and bile. What ends up leaving the stomach and heads to thesmall bowel is chyme –which is semi-digested food.Human Digestive System -The Small IntestineThe body absorbs the molecules and nutrients that have been broken down, when itgoes through the ileum (~5-7 feet long), which is the last section of the smallintestine before it links to the large intestine. The villi lining the wall of the ileumhelp give a large surface for absorption.Nutrients are absorbed through various ways including active transport, endocytosis,facilitative diffusion and passive diffusion.For example:Fatty acids, fat-soluble substances, monoglycerides and cholesterol areabsorbed through simple diffusion.Amino acids are absorbed through active absorption.Sugars like fructose are absorbed with the help of carrier protein molecules.Water and water-soluble substances are absorbed through osmosis. Watersoluble nutrients leave the GI tract in the blood and travel through the portalvein to the liver and then to the heart.The Bodys Fuel + NutritionThe nutrients that come from the food we eat and get broken down are absorbedinto our body and then transported by the blood system and the lymph system to allthe cells and organs in our body. The cells use these nutrients on the molecular levelto give us the energy we need, the ability to heal, the fuel for our cells to do whatthey are supposed to do: like your heart beating!When you smell food or think of food, this triggers the hormones and nervoussystem that coordinates digestion and absorption (like the brains behind it). If youare stressed or sick this can slow the process of digestion down.The Large Intestine -The ColonAt the end of the digestion process, the waste products leave the small intestineswith the help of fiber and enter the colon –the large intestine. The colon reabsorbswater and the friendly bacteria helps process vitamins and nutrients. Any fiber orundigested food that does not get broken down is excreted in the stool. That is howthe digestive system works in a nutshell!You Are What You Eat!There is so much more than we think about that goes into how food processes in thehuman digestive system. The better we understand the process of how the digestivesystem works, the more realize the value of eating healthy and eating a balanceddiet: vegetables, fruits, whole grains and fiber… such as flax seed!
Mouth and EsophagusDigestion begins in the mouth with the grinding of food a mixture of saliva. The saliva breaksdown the chemicals in the food a bit, which helps make the food mushy and easy to swallow.The tounge pushes the food to the back of the mouth and into the esophagus, or gullet.The esophagus is like a stretchy pipe thats about 10 inches (25 centimeters) long. It moves foodfrom the back of your throat to your stomach. Here peristalsis (constriction and relaxation ofmuscles) begins that propels material through the digestive system.(A special flap called the epiglottis covers the opening of your windpipe to make sure the foodenters the esophagus and not the windpipe.)StomachThe stomach is attached to the end of the esophagus. It is the biggest bulge in the digestive tract.It has the following functions:to store the food youve eaten.to break down the food into a liquidy mixture.to slowly empty that liquidy mixture into the small intestine.The strong muscles in the walls of the stomach and the gastric juices that also come from thestomachs walls helps in breaking the food into smaller and smaller pieces. Pepsin, thepredominant stomach enzyme is a potent digester of meats and other proteins.Some points to note:Virtually nothing is absorbed through the stomach walls except alcohol.An ordinary meal leaves the stomach in three to five hours.Watery substances leave the stomach quite rapidly while the fats remain considerablylonger.Most of the process of digestion occurs beyond the stomach.Small IntestineIt is a long tube, twenty-two feet long (see the above pic), where digestion is completedand virtually all absorption of nutrients(vitamins, minerals, proteins, carbohydrates and fats) occurs. It has an alkalineenvironment which is necessary for the most important work of digestion and absorption.The food may spend as long as 4 hours in the small intestine and will become a very thin, waterymixture. The nutrients from the food pass from the intestine into the blood.The nutrient-rich blood comes directly to the liver for processing.Liver - the main storage organ for fat-soluble vitaminsThe liver is the largest solid orgain of the body and weighs about four pounds. It acts as a bloodreservoir and a storage organ for vitamins such as A and D and for digested carbohydrate(glycogen), which is released to sustain blood sugar levels. It manufactures enzymes,cholesterol, proteins, vitamin A (from carotene), and blood coagulation factors.One of the prime functions of the liver is to produce bile. Bile contains salts that promote efficientdigestion of fats.
The liver filters out harmful substances or wastes, turning some of the waste into more bile. Theliver even helps figure out how many nutrients will go to the rest of the body, and how many willstay behind in storage.GallbladderIt is a saclike storage organ about three inches long. It holds bile, modifies it chemically, andconcentrates it ten-fold. Even the sight of food may empty the gallbladder. Constituents ofgallbladder fluids sometimes crystallize and form gallstones.PancreasThis gland is about six inches long and provides the bodys most important enzymes. Itsecretes:Insulin, which accelerates the burning of sugar in the body.Pancreatic juice, which contains some of the bodys most important digestive enzymes -lipases, which split fats;proteases, which split proteins; and amylases, which splitstarches.Large IntestineThe large intestine is almost the last stop on the digestive tract. The leftover waste - remnantsof the food that your body cant use - goes on to the large intestine. The body gets its last chanceto absorb the water and some minerals into the blood. The waste gets harder and harder as itkeeps moving along, until it becomes a solid. Then it is pushed into the rectum. The solid wastestays here until you are ready to go to the bathroom.