Thursday, October 15, 2009

The Mechanics of Digestion

Once we swallow a bite of food, a pill, or slurp a smoothie, the ride begins - as food has to travel down the 30 feet (9 meters) pathway before all is said and done. Fortunately, muscle tone in our organs shortens that length by about half.

Digestion begins in the brain that sends messages to a system of salivary glands. Mechanical digestion
starts in the mouth: My Pink Elephant Still Smells Like Rotten Apples. Starting from Mouth to Pharynz to Esophagus to Stomach to Small Intestine to Large Intestine to Rectum to Anus.

The first part of swallowing is a
flinging back of the food into the upper part of the esophagus by a backward movement of the tongue. This powerful motion is followed by wave-like movements in the distal segments of the gullet, which empty remaining bits of food into the stomach. Mechanical movements of the esophagus, stomach, and intestine keep food passing through the digestive system. The normal movements of the small intestine are rhythmical segmentation, or swaying and pendular, or a peristaltic rush. In the stomach the movement is also peristaltic, kneading and mixing take place only in the strong-muscled pars pylorica. The pylorus does not wait to open until the food is digested. Fluids run out as soon as they are drunk, but solids are being held back until the stomach has a chance to liquefy them. The colon is a sluggish organ with few and slow movements, but a few times a day there are mass movements which carry material usually from the transverse colon over into the sigmoid. These movements may give rise to the final act of digestion, letting organisms eliminate waste from the GI tract.

Healthy peristalsis will let you drink a glass of water while standing on your head, although if not skilled enough it could come out of your nose. Astronauts claim that they do not have any problems digesting food with zero gravity.
The mechanics of the digestive tract can, indeed, be affected by the accessory organs - salivatory glands, pancreas, liver, and gallbladder, enzymes and small molecules helping to digest food.
Reverse peristalsis, vomiting, constipation, delay in absorption, leaky gut, intestinal gases caused by fermentation and by irritating foods, may all upset the gradient.

If you tend to have digestive problems, you may need to lie down at least two hours after you finish a meal, this seems to help some people. It does not work for many others though.
In general, your best bet for maximum digestive efficiency seems to be sitting upright. The Mayo Clinic also suggests that you make sure you're relaxed while you're eating, so that your digestive muscles contract normally.

Digestion time also varies depending on the individual and the type of meal. For healthy adults, it's usually between 24 and 72 hours. After you eat, it takes about six to eight hours for food to pass through your stomach and small intestine. Food then enters your large intestine (colon) for further digestion and absorption of water. Elimination of undigested food residue through the large intestine usually begins after 24 hours. Complete elimination from the body may take several days.
Heartburn - a feeling that food is stack in the throat - is one of digestive problems that is usually made worse by lying down or bending over while eating. It gets better if you sit or stand up.

This happens when food and stomach juices go back into the esophagus. Common causes of this (gastroesophageal reflux or GERD) include:

  • Anatomical abnormalities such as

o incomplete closing of the valve (the lower esophageal sphincter, or LES) between the esophagus and the stomach,
hiatal hernia, which occurs when a small portion of the stomach pushes upward through the diaphragm, which is the muscle that separates the lungs from the abdomen.

  • Pressure on the stomach caused by obesity, frequent bending over and lifting, tight clothes, straining with bowel movements, vigorous exercise, and pregnancy.
  • Smoking
  • Stress, which can increase the amount of acid your stomach makes and cause your stomach to empty more slowly.

Common foods that can worsen reflux symptoms include

  • Citrus fruits
  • Chocolate
  • Drinks with caffeine or alcohol
  • Fatty and fried foods
  • Garlic and onions
  • Mint flavorings
  • Spicy foods
  • Tomato-based foods, like spaghetti sauce, salsa, chili, and pizza

Use of prescription and nonprescription medicines, such as aspirin, ibuprofen, prednisone, iron, potassium, antihistamines, or sleeping pills is also one of common causes.

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