Digestion: a gut reaction

by Karen Bowen

It’s time for a fall digestive system check. Begin with a quick walk-around to note any obvious issues, overload or leakage. Then, get acquainted with each part: mouth, esophagus, stomach, small intestine, and large intestine to ensure it is working properly.

Begin with the mouth, where teeth cut and grind food, and saliva is added. Saliva starts digestion by breaking down starches. Saliva’s mucin, a major protein in mucus, lubricates the food to help you swallow. Mucin also holds chewed food together, forming the bolus which is pushed into the esophagus during swallowing.

Next, consider the esophagus, a muscular tube connecting the mouth and stomach. Its muscular walls contract in waves (peristalsis) to push the food bolus to the stomach. No digestion occurs in the esophagus because it is just a food passageway.

After your food reaches the stomach, it is churned into a paste-like material, mixed with some gastric juice and it eventually forms chyme. A pepsin enzyme which is inactive (pepsinogen) is activated and converted to pepsin to digest protein.

As well, pits in the stomach wall produce gastric juices. Eating, smelling, tasting or even just thinking of food can trigger their production. One juice, hydrochloric acid, lowers the pH of the stomach contents to an extremely acidic environment. This kills most microbes in food, including many that might cause sickness.

It seems hard to believe that with such an extreme pH environment, your stomach does not digest itself! Fortunately, it is protected by a fairly thick coating of alkaline mucus. However, when this lining breaks down, an ulcer can form. Currently, ulcers are believed to be caused by infection which is now quite successfully treated with antibiotics (instead of antacids).
Not much is absorbed in the stomach, only a few small molecules such as aspirin and alcohol, which explains why their effects are felt so quickly. Other materials must wait to be absorbed in the small intestine.

In the small intestine, (about seven meters long and one inch in diameter) most chyme is broken down into these molecules: simple sugars, amino acids and nucleotides, which are then absorbed into the bloodstream. Several other major organs contribute to this process, including: the pancreas, liver and gall bladder.

When chyme stretches the intestinal wall, cells of the intestinal lining secrete intestinal juices and mucus, usually, two to three litres of fluid each day.

The inner surface of the small intestine is highly textured with microscopic finger-like projections called villi. These villi create a large surface area available for absorption. Each villus is, in turn, covered with small projections called microvilli which further increase surface area, creating a surface area of over 150 times that of your skin.

Each villus is filled with a dense capillary network surrounding a centrally located lymphatic vessel, a lacteal. The lacteal absorbs the products of lipid digestion such as fatty acids. From the lacteal, microscopic fat droplets are carried through lymph vessels into a large vein in the neck.

However, most non-fatty nutrients, which diffuse directly into the blood capillaries of the intestinal villi, are carried to the liver and removed from the bloodstream.

By the time digested food gets to the end of the small intestine, almost all nutrients and water have been removed. This nutrient depleted chyme is then pushed into the large intestines.

The final steps of chemical digestion take place in the large intestines. Made up of six parts, the large intestines process the remaining undigested food to prepare to eliminate it. Here, the large intestines absorb remaining water, salt, and minerals.
This chyme travels to the final stop valve, the anus, which regulates the final elimination. Its pressure-sensitive neurons detect when solids have accumulated and initiate the defecation reflex.

Fortunately, one of the two anal sphincters is under voluntary control, so you can consciously control the expulsion of feces until a convenient time.

Now that you’ve reacquainted yourself with your digestive system, follow these nine tips to maintain its optimum condition:

Eat more fruits and vegetables to add roughage and enzymes; drink lots of water to keep your stools soft; eat less fatty foods to take the strain off your liver and gall bladder; avoid processed foods to retain vital nutrients; eat slowly and moderately to allow your body time to break down the food and signal when you are full; quit smoking to reduce the poisons your organs filter; drink less alcohol to protect your stomach lining and liver; exercise regularly to create strong muscles to move your food along more effectively; and reduce personal stress to reduce stress hormones which interfere with digestion.

Following these pointers will help avoid abdominal distress, bloating, gas, stomach and colon discomfort, aches and pains, vomiting, diarrhea and headaches. Go with your gut!

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