The digestive system plays an important role in the absorption of nutrients into the body. It takes the food we ingest, breaks it down mechanically and chemically in the mouth and stomach. It then absorbs nutrients, fats, proteins and water in the intestines before eliminating the waste through the rectum
Answer:
Chewing: Ingestion 1
Chewing mechanically mixes food with saliva from the salivary glands. Amylase in saliva chemically digests starch in the food. The mixing process is lubricated by mucin, a slippery protein in saliva. Each mouthful takes approximately 30–60 seconds.
Swallowing: Ingestion 2
The food is formed into a small ball called a bolus, which is pushed to the back of the mouth by the tongue. Involuntary muscle contractions in the pharynx then push the bolus down towards the oesophagus. This swallowing reflex takes about 1–3 seconds.
Peristalsis: Ingestion 3
In the oesophagus, the bolus is moved along by rhythmic contractions of the muscles present in its walls. For a medium-sized bolus, it takes about 5–8 seconds to reach the stomach.
Time to empty: Stomach
Food is mixed with gastric juice. Strong muscular contractions in the stomach wall reduce the food to chyme – a thick milky material. The pyloric sphincter at the lower end of the stomach slowly releases chyme into the duodenum. Emptying the stomach takes 2–6 hours.
Time to empty: Small intestine
It takes 3–5 hours from entry to the duodenum to exit from the ileum. 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.
