The acid/base balance is expressed in terms of pH. An acidic environment has a pH of less than 7.4, whereas a basic or alkaline setting has a pH of greater than 7.4. Molecules that give off hydrogen maintain an acidic pH. In contrast, alkaline molecules attract hydrogen. The human body works best when it remains close to neutral, 7. You come equipped with numerous controls that activate whenever the pH shifts one way or another. Yet, the individual organ systems of your body maintain balance even though their different components have differing pH values. The digestive system exemplifies this balancing act.
Digestion, Phase 1
In order for you to take food in, grind it up, extract nutrients and then excrete what’s left over, the digestive tract has to juggle varying pH values. Generally, your body maintains an overall pH of 7 to 7.4. However, your mouth -- the first stop in the digestion process -- has a pH of 6.8 which reflects the input of digestive juices from the parotid and salivary glands. The secretions cause the pH of the mouth to begin to drop toward acidic. This helps your food get a head start on digestion as it moves from your mouth to your pharynx and through your esophagus. All three organs hold steady at a pH of 6.8.
Digestion, Phase 2
As you chew, the food becomes a bolus. The bolus gets propelled by the muscular contractions of your swallow. When the food enters your stomach, it encounters the highly acidic pH of 1.3. Due in large part to the secretion of hydrochloric acid, the change in pH enables the dismantling of food. The stomach churns the food into chyme and kills unwanted germs in preparation for the small intestine. At the first section of the small intestine, the chyme enters your duodenum, which has a pH of 6 to 6.5. The acidity level begins to descend as the pH value rises.
Digestion, Phase 3
The chyme moves further into the small intestine which becomes slightly more alkalinic at a pH of 7 to 8. The intestines do not need a highly acidic terrain as does the stomach, because, it doesn’t need it. Its job is absorbing vitamins and minerals. Once the small intestine absorbs the important nutrients, the chyme propels along by peristalsis, muscular contractions, to the large intestine. Upon entering the large intestine, there is a change in pH to 5.5 to 7. Very little absorption takes place there. The bowel prepares to evacuate the leftover waste from the body.
Why the pH Varies
In order to carry out their individual functions, each section of the digestive system maintains a pH that suits the needs of the environment. The first part of the system prepares the food for digestion. This section’s weak acidic surroundings begin the process. The second area, the stomach, must supply enough acid to break the food into its nutrients. However, when the food continues into the intestines, it no longer needs acid. Both intestines bring the matter closer to the pH of the body.
- Kennesaw State University: Anatomy of the Gastrointestinal Tract and Drug Absorption
- "Textbook of Medical Physiology;" Guyton and Hall; 1996
- "Dorland's Illustrated Medical Dictionary;" Saunders; 2007
- "Human Anatomy;" Martini and Timmons; 1997