Chapter One
Normal Digestion
A good many things go around in the dark besides Santa Claus.
-- Herbert Hoover, 1935
Gas, burps, stomachaches, and bloating are standard fodder for comedy routines -- because of their frequency as much as the discomfort and embarrassment they cause. Digestive disorders are among the most common problems we experience. Recent figures show that almost half the U.S. population experiences heartburn regularly, one in five are lactose intolerant, and colon and rectal cancer are second only to lung cancer as a leading cause of cancer deaths.
In order to understand the impact of a malfunction in the digestive tract and why it leads to all of the symptomatic manifestations of celiac disease, it is necessary to understand how the body normally digests and absorbs food.
Food keeps my body running and it keeps me up at night. (Gary, 49)
The digestive system has been des
Chapter One
Normal Digestion
A good many things go around in the dark besides Santa Claus.
-- Herbert Hoover, 1935
Gas, burps, stomachaches, and bloating are standard fodder for comedy routines -- because of their frequency as much as the discomfort and embarrassment they cause. Digestive disorders are among the most common problems we experience. Recent figures show that almost half the U.S. population experiences heartburn regularly, one in five are lactose intolerant, and colon and rectal cancer are second only to lung cancer as a leading cause of cancer deaths.
In order to understand the impact of a malfunction in the digestive tract and why it leads to all of the symptomatic manifestations of celiac disease, it is necessary to understand how the body normally digests and absorbs food.
Food keeps my body running and it keeps me up at night. (Gary, 49)
The digestive system has been described as the outside world going through us. Designed to supply the body with all of the nutrients and fluids it needs to function, it is essentially a long tube that is open at both ends. Food enters at one end, the nutrients the body can use are absorbed by the lining of the gastrointestinal tract, and nondigested residue is excreted from the other end. The concept is simple, the design and execution quite remarkable.
The Gastrointestinal (GI) Tract
Food enters the GI tract via the mouth; moves through the pharynx, esophagus, stomach, small intestine (the duodenum, jejunum, and ileum), and large intestine (colon), and exits from the anus. The salivary glands, pancreas, liver, and gallbladder are organs that secrete the enzymes and fluids that help digest food. They are connected to the digestive system by ducts.
The digestive system, or gut, is intimately related to the following:
- the circulatory system, which transports the nutrients from the intestine to the tissues throughout the body and liver
- the enteric nervous system, which helps control enzyme release and muscular contractions of the gut
- the muscles of the digestive system, which provide motility to help digest and move food through the long tract
If one section of the system malfunctions, it almost necessarily affects another, and there are numerous places for things to go wrong.
Digestion
Digestion is the word commonly used to describe a three-part process:
Digestion -- the breakdown of food products into ever smaller and smaller components that can be absorbed.
Absorption -- the passage of food products that have been broken down into the intestinal wall.
Transport -- the transfer of food from the intestinal wall to the cells of the body.
Digestion requires the following:
- the chemical breakdown of food by enzymes
- the mechanical mixing and propulsion of the products of chemical activity by the intestinal muscle
Digestion actually begins before the food even enters your mouth. When you see, think about, or smell food, the vagus nerve transmits a chemical message from your brain to release saliva in the mouth, increase stomach motility, and release gastric acid in the stomach. We begin to salivate and the stomach "rumbles" at the very anticipation of food.
The Mouth
In the mouth, chewing tears the food apart and grinds it into smaller components. Saliva, a mucous substance, is secreted to lubricate and start to dissolve the food. It contains various enzymes that start the digestion of fats and carbohydrates that are continued farther down the digestive tract. Saliva also acts as a glue to hold the food together as it travels toward the stomach.
We swallow the ball or bolus of chewed food and saliva, and it is transported down our esophagus. While the skeletal muscles at work in the mouth and throat are voluntary -- we consciously move our jaws and swallow -- smooth muscles that function involuntarily take over in the esophagus. The gut actually has its own pacemaker. An undulating contraction of muscles called peristalsis begins and moves the food into the stomach where the action, quite literally, really starts.
The Stomach
The stomach is a big muscular sac or reservoir that holds the chewed food until it is ready to move on, mixes it with gastric juices, and starts many of the chemical processes of digestion. The muscular movements of the stomach act like a Cuisinart -- chopping, blending, and mixing the ball of food to form a soupy puree called chyme.
The stomach secretes an enormous amount of gastric acid, which functions to both break down the food and convert the stomach into a disinfecting tank, killing bacteria and inactivating toxins in the food we have eaten.
Pepsin, an enzyme secreted by the stomach, starts the digestion of protein.
The stomach also sends messages (in the form of hormones) to the other digestive organs telling them that food has arrived. This stimulates the secretion of pancreatic juices and bile from the liver and gallbladder that will further break down the chyme once it moves into the small intestine. The only substances that are absorbed directly into the bloodstream in the stomach are aspirin and alcohol.
One-Way Street
The sphincters that connect the esophagus to the stomach and the stomach to the small intestine are one-way valves. Food is only meant to travel down the GI tract -- a street sign that is often ignored. Occasionally, chyme refluxes or backs up into the esophagus -- a condition known as GERD, gastroesophageal reflux disease -- and the gastric acid becomes a corrosive agent on the less well-protected lining of the esophagus. (See Chapter 3.)
When the chyme is sufficiently liquefied, muscle/peristaltic contractions gradually push it into the upper part of the small intestine, the duodenum. The stomach empties in a slow and controlled way so as not to overwhelm all the mechanisms of digestion in the small intestine.
As the small intestine fills with chyme, it signals the stomach to decrease its activity and slow down the emptying process. This is one reason a large meal "stays with you"; i.e. it lingers in the stomach until the small intestine can process it.
Continues...
Excerpted from Celiac Diseaseby Peter Green Copyright © 2006 by Peter Green. Excerpted by permission.
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