If you are like most people, you take your digestive system for granted. As long as it is working well, you seldom think of it. Actually, your digestive system is really a wonderful piece of work. It is a strong dependable work horse – the body’s Clydesdale. It is always waiting patiently for the next batch of food to come down the pipe. It never sleeps or stops to take a break, and none of this requires any conscious action on your part. Your gut makes it possible for you to feast on fried chicken or three-alarm chili without having to understand anything about the complex science of digestive chemistry.
Your gut feeds you
You may think that you feed your gut. Actually, your gut feeds you. Most of the food you eat would be as deadly as poison if it got directly into your bloodstream. Your gut can best be described as a very elaborate food “disassembly” plant. Except for dietary fiber – nut husks, bran, celery strings and such – your gut disassembles virtually everything you eat into smaller components, ones that your body can use. Your gut converts the crisp fat in your breakfast bacon into smaller fatty acids. It turns the protein in your dinner lamb chop into smaller amino acids. It changes the large carbohydrates in your mashed potatoes into sugary glucose. Then it passes these much simpler nutrients to your blood system – food which your trillions of cells can use for energy, body growth and repair. This process of breaking down large molecules into their smallest parts so the body can use them is termed digestion. Without the chemical wizardry of digestion, even though you gorged yourself, you would soon starve to death. So, your gut feeds you. Your entire digestive system from your mouth to your anal sphincter is a single, long, hollow, muscular tube – about thirty feet long. Without any effort on your part, the muscles in this intestinal tube contract and relax to move food and fluids along the digestive tract for processing.
Down the hatch – your esophagus
Of course, digestion begins when your food is first broken down into smaller pieces by your jaws and teeth and mixed with saliva – up to two quarts a day. After chewing and swallowing, your food is propelled down the ten inches of esophagus, or “foodpipe,” and into your stomach. At the lower end of the esophagus, a one-way valve – named the lower esophageal sphincter – prevents the backsplash of stomach contents upward into your esophagus. A malfunction of this valve is the most common cause of heartburn.
Your stomach pouch
Most animals, including human beings, have a single stomach, but birds, cows and sheep have two or more chambers to their stomachs. Empty, the volume of your stomach “pouch” is less than one-half cup. As you eat, its muscular wall can relax and expand to hold about three pints of sustenance. Then about every twenty seconds, contractions called peristaltic waves ripple through your stomach squeezing gently in the upper part, more powerfully lower down. This churning motion mixes the food particles with powerful hydrochloric acid and the enzyme, pepsin. Enzymes are like crowbars that break apart other large molecules. Produced by the stomach, these strong chemicals convert the food to about the consistency of cream of potato soup. Eventually, the now liquefied food is squirted a little bit at a time through another one-way valve and into the small intestine. Only water, alcohol, and certain drugs seem to be absorbed by the stomach; most food absorption takes place in the small intestine.
Liver and pancreas
There are also two solid organs, the liver and the pancreas, that produce digestive juices which accelerate the disassembly process. These juices reach the small intestine through little tubes, or ducts. The liver makes bile which is temporarily stored in the gallbladder and carried down the bile duct to mix with the food. The pancreas produces enzymes which are carried down the pancreatic duct to further aid in the process of digestion. The pancreas also has the job of producing insulin to regulate the level of sugar in your blood. A malfunction here leads to diabetes.
Twenty feet of small intestine
In the middle of your abdomen lies the twenty foot long small intestine. It is here that the final process of digestion and nutrient absorption takes place from the two gallons of food, liquid, and digestive secretions you process each day. The small intestine is divided into three sections: the first part called the duodenum, the middle portion, referred to as the jejunum, and the last part called the ileum. The entire small intestine is lined with intricate sets of muscles which are never at complete rest. One group produces a swaying motion that churns together food and digestive juices. Another set of muscles produces a wavelike action; the waves push the contents along a few inches, then die out. These muscular contractions cause a ripple-like movement that carries the contents down the small intestine – somewhat like a conveyor belt.
To maximize absorption, the food molecules must come in contact with a large number of specialized intestinal cells. To accomplish this, the walls of your intestines are covered with microscopic hair like projections called microvilli. Each square inch of intestine contains about 10 billion microvilli. This increases the surface area for food absorption dramatically. In fact, if your intestinal interior were smooth, it would present only about 6 square feet of absorptive surface. Instead, because of these microvilli, it presents almost 4000 square feet – about the same surface as two tennis courts! Microvilli contain special cells which enable absorption of nutrients into your bloodstream. It takes the small intestine about four hours to process a meal. Once all the “good stuff” is removed, your gut passes the indigestible watery gruel that is left to the last five feet of your digestive tract, the colon.
Your colon – recycling precious water
Sometimes called the large intestine because of its wider diameter, the colon is actually much shorter than the small intestine, only about 5 feet long. The colon begins in the cecum located in the lower right portion of your abdominal cavity. Your appendix is connected to the cecum, and that is why appendicitis causes pain in the right lower side of the abdomen. At the junction of the small intestine and the cecum there is a valve, called the ileocecal valve, that prevents material from the cecum from moving backward into the ileum. Your cecum continues as the ascending colon upward along your right side. Just under the liver it makes a sharp turn. The colon continues across the upper abdomen as the transverse colon, only to make another sharp downturn. The colon continues straight down your left side as the descending colon and then into an S-shaped segment called the sigmoid colon. This is the area where most “pockets” of diverticulosis form. The sigmoid colon connects to the last six inches called the rectum. The rectum continues directly into the short anal canal which terminates with the anal sphincter. The anal sphincter is a valve that must remain closed to prevent stool incontinence and open properly to permit a bowel movement. Some observers have referred to the anal sphincter muscle as the social muscle, because it is able to prevent accidental bowel movements and to distinguish between passing gas as opposed to solids and liquids.
While the esophagus, stomach and small intestine contain very few bacteria, or germs, the colon is full of trillions of bacteria. In fact, there are more intestinal bacteria in your colon at this moment than there are human beings who have ever lived. For the most part, these are healthy bacteria that cause no problems as long as they are confined to the inner opening of the colon. If a hole occurs in the wall of the colon and the bacteria escape into the abdominal cavity, serious infection occurs – called peritonitis.
There is no nutrient absorption in the colon. The colon’s main job is to reclaim the excess water from the intestinal waste and recycle it back into your bloodstream for reuse. Think of it like a “water treatment plant.” As the liquid waste moves along, it is gradually dried and forms a solid sludge which can be expelled as a bowel movement, also known as stool or feces.
When your digestive system is working normally, you should not even be aware of all of these complicated functions. It is on “autopilot” waiting to serve you. However, sometimes it malfunctions leading to distressing and embarrassing symptoms, and occasionally, it can be the site of a serious ailment. That is when you begin to become aware of your digestive system. Don’t be embarrassed if you have persistent intestinal problems. Consult your doctor.