Question

Which of the following digestive juices have the minimum pH?
A. Bile
B. Saliva
C. Gastric juice
D. Pancreatic juice

Answer 1

Hint: Digestive juices are secretions of digestive glands that aid in digestion of food in the alimentary canal. The associated digestive organs are salivary glands, stomach, liver, pancreas and small intestine. Our digestive system requires different digestive juices to carry out complete digestion of food. This is because one juice does not contain all the required enzymes for digestion.

Complete answer:
When a person eats food, the action stimulates the secretion of digestive juices. As the chewed food or bolus moves through the oesophagus into the stomach, the food is acted upon by the gastric secretions. Inside the stomach, the food is mixed with gastric juices and forms a chyme.
The wall of stomach or mucosa is covered with epithelial lining that contains numerous gastric pits. These pits lead to the gastric glands. Parietal cells or oxyntic cells lie in the middle and chief cells in the basal region of the gastric glands. They secrete a large amount of gastric secretions. This secretion contains hydrochloric acid, intrinsic factors, pepsinogen, bicarbonate and mucus. Due to the presence of hydrochloric acid, this secretion is highly acidic (pH 1.5 to 3.5) in nature. Pepsinogen is a proenzyme of pepsin which facilitates the digestion of proteins. First the hydrochloric acid denatures the proteins and then by hydrolysis of pepsinogen into pepsin, digestion of protein takes place. After a meal, the acidity inside the stomach is maintained around pH -3 for approximately 90 minutes.

Thus, the correct answer is option (C), Gastric juice.

Additional information:
The pH range of saliva is 6.5 - 7.5, bile juice is 7 - 8, pancreatic juice is 7.5 - 8.2 (alkaline) and intestinal juice is 7 – 8 (alkaline).

Note:
The gastric juice secreted by mucosa is 1.2 to 1.5 litres per day. The walls of the stomach are lined by a protective membrane which prevent auto-digestion by the action of digestive juices. This membrane contains mucus and lipoproteins and is thus resistant to the acid. The acidity of gastric acid kills ingested microbes and also limits bacterial growth thereby preventing intestinal infections.