The acid bag

The idea

Gastric glands release hydrochloric acid, which makes the medium acidic for the protein-digesting enzyme pepsin, and mucus, which protects the stomach lining from the acid; a sphincter releases food in small amounts into the small intestine.

Strong acid inside

The stomach contains hydrochloric acid. Acid can damage tissue, yet the stomach wall stays healthy.

What do you think keeps the stomach lining safe?

• A layer of mucus
• The acid is very weak
• The stomach has no lining

Inside the stomach

Press Next step to see what the gastric glands release.

A protected acid bath

Gastric glands release hydrochloric acid, pepsin and mucus. The acid makes the stomach acidic, and in that acidic medium the protein-digesting enzyme pepsin works well. The mucus shields the lining of the stomach from the acid. At the exit a sphincter releases the food into the small intestine in small amounts.

Gastric glands release hydrochloric acid, which makes the medium acidic for the protein-digesting enzyme pepsin, and mucus, which protects the stomach lining from the acid; a sphincter releases food in small amounts into the small intestine.

Notes

Gastric glands release hydrochloric acid (acidic medium for pepsin) and mucus (protects the lining); a sphincter lets food into the small intestine in small amounts.

Check yourself

What does hydrochloric acid do in the stomach?

Which protein-digesting enzyme do the gastric glands release?

What protects the inner lining of the stomach from the acid?

What controls the exit of food from the stomach into the small intestine?

• It makes the medium acidic so that pepsin can act — correct. Yes!
• It breaks starch into simple sugar. Starch is broken into simple sugar by salivary amylase in the mouth. The acid makes the medium suitable for pepsin.
• It protects the inner lining of the stomach. The mucus protects the lining from the acid.
• Salivary amylase. Salivary amylase is in saliva and breaks down starch.
• Pepsin — correct. Yes!
• Lipase. Lipase is in pancreatic juice and breaks down emulsified fats.
• Bile. Bile is made by the liver and acts in the small intestine.
• Pepsin. Pepsin is an enzyme that digests proteins; it is the mucus that protects the lining.
• Mucus — correct. Yes!
• A sphincter muscle that releases it in small amounts — correct. Yes!
• The anal sphincter. The anal sphincter regulates the exit of waste material at the anus.
• The muscles of the tongue. The muscular tongue mixes the food with saliva in the mouth.