The small intestine’s structure of folds, villi and microvilli increases the absorptive surface area and allows maximum exposure to enzymes and complete absorption of the end products of digestion. It takes 3–5 hours from entry to the duodenum to exit from the ileum. The pyloric sphincter at the lower end of the stomach slowly releases chyme into the duodenum. Strong muscular contractions in the stomach wall reduce the food to chyme – a thick milky material. Time to empty: Stomachįood is mixed with gastric juice. For a medium-sized bolus, it takes about 5–8 seconds to reach the stomach. In the oesophagus, the bolus is moved along by rhythmic contractions of the muscles present in its walls. This swallowing reflex takes about 1–3 seconds. Involuntary muscle contractions in the pharynx then push the bolus down towards the oesophagus. The food is formed into a small ball called a bolus, which is pushed to the back of the mouth by the tongue. Each mouthful takes approximately 30–60 seconds. The mixing process is lubricated by mucin, a slippery protein in saliva.
Amylase in saliva chemically digests starch in the food. Chewing mechanically mixes food with saliva from the salivary glands.
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