The Human Digestive System — Which Enzyme Acts Where

Why This Chapter Is Worth Two Marks

Digestion questions are almost always a single fact: which enzyme acts where, on what, and what it produces. Learn that map and the questions collapse.

The pathway: mouth → pharynx → oesophagus → stomach → small intestine (duodenum → jejunum → ileum) → large intestine (caecum → colon → rectum) → anus. The whole alimentary canal is about 9 metres long, and the small intestine is its longest part, roughly 6 metres.

Four separate processes, and options love to mix them up:

• ›Digestion — breaking large food molecules into absorbable ones.
• ›Absorption — passing them into blood or lymph, mostly through the villi of the small intestine.
• ›Assimilation — using them inside the body's own cells.
• ›Egestion — expelling what is left.

Three digestive glands sit outside the canal and pour their secretions into it: the salivary glands, the liver (the largest gland in the body) and the pancreas (the largest mixed gland).

1. Which of the following digestive juices contains no enzyme at all?

2. Salivary amylase, also called ptyalin, acts on:

3. Enterokinase, secreted by the small intestine, converts:

4. The largest gland in the human body is the:

5. The pH of gastric juice in a healthy human stomach is about:

6. In the human body, vitamin K is synthesised by bacteria living in the:

7. Digested fat — fatty acids and glycerol — is absorbed mainly into:

8. Rennin, the enzyme that curdles milk, is present in the gastric juice of: