Which of the following is NOT the main intestinal enzyme?

Appeared in: BTSC 3 August 2025

Explanation

Lingual lipase is the correct answer because it is not a primary intestinal enzyme.
It is secreted by serous glands on the tongue to begin fat digestion.
This enzyme is swallowed with food and becomes active in the acidic environment of the stomach, not the small intestine.

Option A: Lactase is a key intestinal enzyme. It is located on the brush border of the enterocytes (cells lining the small intestine) and is essential for digesting lactose (milk sugar) into glucose and galactose.
Option B: Proteases are a major class of intestinal enzymes. Enzymes like trypsin and chymotrypsin are secreted by the pancreas into the small intestine, while peptidases are present on the intestinal brush border. They are all crucial for breaking down proteins.
Option C: While salivary amylase begins carbohydrate digestion in the mouth, pancreatic amylase is a major enzyme secreted into the small intestine to continue the breakdown of starches and complex carbohydrates.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of digestion and enzyme action as background academic context rather than a clinical decision trigger.
Understanding the sites of enzyme action is crucial for diagnosing malabsorption disorders. For example, a deficiency in lactase leads to lactose intolerance, causing symptoms like bloating, gas, and diarrhea after consuming dairy.
Pancreatitis (inflammation of the pancreas) can impair the secretion of proteases and amylase, leading to poor digestion of proteins and carbohydrates, resulting in steatorrhea (fatty stools) and malnutrition.
What if? - If a patient has a condition causing gastric achlorhydria (lack of stomach acid), the activation of lingual lipase would be significantly reduced, impairing the initial stages of fat digestion even before the chyme reaches the intestine.

How to Approach the Question

First, identify the core of the question, which is to find the enzyme that is NOT a 'main intestinal enzyme'.
Note the negative keyword 'NOT'. This means three of the options are intestinal enzymes, and one is not.
Review each option and recall its source (where it's made) and its primary site of action (where it works).
Lactase: Made and acts in the small intestine. It's an intestinal enzyme.
Proteases (e.g., trypsin): Made in the pancreas, acts in the small intestine. It's an intestinal enzyme.
Amylase (pancreatic): Made in the pancreas, acts in the small intestine. It's an intestinal enzyme.

Concept Tested & Keywords

Concept Tested: Physiology of digestion and enzyme action
Stem keywords: intestinal enzyme
Lead-in keywords: NOT
Negative lead-in flag: The question uses the negative keyword 'NOT', requiring identification of the option that does not fit the criteria.

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E6 Nursing Brunner Adult Health 3SA Vol 1 Part 2 p. 72-74

Practise the full BTSC 3 August 2025

Attempt every question from this paper in a timed mock, then review the full solution for each one.