Quick answer: The gastric glands in the stomach wall release hydrochloric acid, the protein-digesting enzyme pepsin and mucus. The acid makes the stomach acidic so pepsin can work and kills many germs; pepsin starts breaking down proteins; mucus protects the stomach lining from the acid and enzyme. If the lining is not protected, sores called peptic ulcers can form.
Gastric juice and its components
Food reaches the stomach through the oesophagus. The muscular stomach wall churns the food, and gastric glands in its lining release gastric juice (roughly 2 litres a day in an adult).
| Component | Main job |
|---|---|
| Hydrochloric acid (HCl) | Makes the stomach strongly acidic; helps pepsin act; kills many microbes in food |
| Pepsin | Begins the digestion of proteins |
| Mucus | Protects the inner lining of the stomach from the acid and pepsin |
These three components are exactly what NCERT names for the stomach.
Hydrochloric acid
Hydrochloric acid is made by special cells in the gastric glands (parietal or oxyntic cells). It keeps the stomach contents at a pH of about 1.5–3.5.
- Acidic medium for pepsin: Pepsin works best in an acidic medium. HCl also converts the inactive form, pepsinogen, into active pepsin.
- Kills germs: The acidity destroys many bacteria that enter with food and water.
- Helps break down food: It helps soften food and loosen tough tissue in it.
Pepsin
Pepsin is released (by chief cells) in an inactive form called pepsinogen. In the acidic stomach it becomes active pepsin:
Pepsin then begins protein digestion:
Why is pepsin released in an inactive form? If it were active inside the cells that make it, it could digest those cells' own proteins. Releasing it as pepsinogen means it becomes active only inside the stomach cavity.
Mucus: the protective layer
Mucus is a thick, slimy layer made by mucous cells in the stomach lining. It contains bicarbonate, which makes it slightly alkaline.
- It forms a barrier between the stomach lining and the acid.
- It stops pepsin from digesting the stomach's own tissue.
- It keeps the lining moist and helps food move along.
Exam answer: "Mucus protects the inner lining of the stomach from the action of hydrochloric acid and pepsin. Without it, the acid would damage the stomach wall and could cause ulcers."
Peptic ulcers and Helicobacter pylori (extension)
A peptic ulcer is an open sore in the lining of the stomach or the first part of the small intestine (duodenum). It forms when the protective layer is damaged and the acid and pepsin attack the tissue underneath.
- For many years, ulcers were blamed mainly on stress, spicy food and too much acid.
- Barry Marshall and Robin Warren showed that a spiral-shaped bacterium, Helicobacter pylori, is a major cause. They received the 2005 Nobel Prize in Physiology or Medicine.
- H. pylori lives in the mucus layer and weakens the stomach's protection.
- Long-term use of some painkillers (such as aspirin and ibuprofen) is another common cause.
- Ulcers caused by H. pylori are treated with antibiotics together with medicines that reduce acid.
Syllabus note: NCERT Class 10 covers the three components of gastric juice and their roles. The details of ulcers, H. pylori and the cell types are extra background and are not required for the Class 10 exam.
Summary table
| Component | Made by | Function | If it fails |
|---|---|---|---|
| HCl | Parietal (oxyntic) cells | Acidic medium, activates pepsin, kills germs | Poor protein digestion, more infections |
| Pepsin | Chief cells (as pepsinogen) | Starts protein digestion | Proteins are digested less in the stomach |
| Mucus | Mucous cells | Protects the stomach lining | Lining is damaged; ulcers can form |
Exam tips
- Name all three components of gastric juice: HCl, pepsin and mucus, each with one function.
- For "why doesn't the stomach digest itself?", give two points: mucus protects the lining, and pepsin is released inactive as pepsinogen.
- Remember the acid's two roles from NCERT: it creates an acidic medium for pepsin and kills bacteria.
- Protein digestion only begins in the stomach; it is completed in the small intestine.
Common mistakes
- Writing that the stomach digests carbohydrates with pepsin. Pepsin acts on proteins.
- Saying HCl digests food by itself. Its main role is to provide the acidic medium and kill germs.
- Thinking protein digestion is finished in the stomach. Pepsin produces smaller fragments; the small intestine completes it.
- Saying ulcers are caused only by spicy food. Infection with H. pylori and some painkillers are major causes.
Frequently Asked Questions
What are the components of gastric juice?
Gastric juice contains hydrochloric acid, the enzyme pepsin and mucus, all released by the gastric glands in the stomach wall.
What is the role of hydrochloric acid in the stomach?
It creates an acidic medium in which pepsin can act, converts pepsinogen into pepsin, and kills many of the bacteria that enter with food.
What is the function of mucus in the stomach?
Mucus protects the inner lining of the stomach from hydrochloric acid and pepsin, so the stomach does not digest itself.
Why is pepsin secreted as pepsinogen?
If pepsin were active inside the cells that make it, it could digest those cells. It is released inactive and becomes active only in the acidic stomach.
What causes peptic ulcers?
Peptic ulcers form when the stomach's protective layer is damaged and acid attacks the lining. Infection with Helicobacter pylori and long-term use of some painkillers are major causes.