4. It really does not fancy acidity
The stomach produces hydrochloric acid. This helps to begin digestion, and it kills many harmful microorganisms that might have been swallowed along with the food. The enzymes in the stomach work best in acidic conditions – in other words, at a low pH. This acidity is what reason what causes peptic ulcers which are ‘wounds in the stomach wall’ that can cause bloody or black stools.
When food is then processed by the stomach, the end result is a very acidic mixture of proteins, acids, and other substances that the body needs.
After the stomach, food travels to the small intestine. The enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. A green pigment called bile neutralises the acid and provides the alkaline conditions needed in the small intestine.
The only problem is that the small intestine really hates acidic items. To counter these acids, the small intestine will produce secretions that are very alkaline in nature so that the food can be processed. Sometimes these alkaline materials come from the wall of the intestine, while others might come from the liver or the pancreas.
The intraluminal pH is rapidly changed from highly acid in the stomach to about pH 6 in the duodenum. The pH gradually increases in the small intestine from pH 6 to about pH 7.4 in the lowermsost part of the ileum.
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