Question

c. The chyme that enters the small intestine is almost free from bacteria but acidie instead. What is the
reason behind this?​

Answer 1

Chyme or chymus (/kaɪm/; from Greek χυμός khymos, "juice"[1][2]) is the semi-fluid mass of partly digested food that is expelled by the stomach, through the pyloric valve, into the duodenum[3] (the beginning of the small intestine).

Chyme results from the mechanical and chemical breakdown of a bolus and consists of partially digested food, water, hydrochloric acid, and various digestive enzymes. Chyme slowly passes through the pyloric sphincter and into the duodenum, where the extraction of nutrients begins. Depending on the quantity and contents of the meal, the stomach will digest the food into chyme in anywhere between 40 minutes to 3 hours at most.[citation needed]

With a pH of approximately 2, chyme emerging from the stomach is very acidic. The duodenum secretes a hormone, cholecystokinin (CCK), which causes the gall bladder to contract, releasing alkaline bile into the duodenum. CCK also causes the release of digestive enzymes from the pancreas. The duodenum is a short section of the small intestine located between the stomach and the rest of the small intestine. The duodenum also produces the hormone secretin to stimulate the pancreatic secretion of large amounts of sodium bicarbonate, which then raises pH of the chyme to 7. The chyme then moves through the jejunum and the ileum, where digestion progresses, and the nonuseful portion continues onward into the large intestine. The duodenum is protected by a thick layer of mucus and the neutralizing actions of the sodium bicarbonate and bile.

At a pH of 7, the enzymes that were present from the stomach are no longer active. This then leads into the further breakdown of the nutrients still present by anaerobic bacteria, which at the same time help to package the remains. These bacteria also help synthesize vitamin B and vitamin K, which will be absorbed along with other nutrients.