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UP CHO - 10 September 2021

Applied Physiology (E5)

Easy

Appeared in: UP CHO - 10 September 2021

Explanation

The process of protein digestion begins in the stomach.
Gastric glands in the stomach wall secrete gastric juice, which contains hydrochloric acid (HCl) and an inactive enzyme called pepsinogen.
The highly acidic environment of the stomach (pH 1.5-3.5) converts pepsinogen into its active form, pepsin.
Pepsin is a proteolytic enzyme that breaks down large, complex protein molecules into smaller, simpler units called polypeptides and peptones.

Option A: The liver produces bile, which is essential for the emulsification (breakdown of large globules into smaller droplets) of fats, not the chemical digestion of proteins.
Option B: The large intestine's primary functions are the absorption of water and electrolytes from remaining indigestible food matter and then to pass useless waste material from the body. It does not secrete digestive enzymes.
Option C: Although the majority of protein digestion and absorption is completed in the small intestine by enzymes from the pancreas and intestinal wall (like trypsin), the initial breakdown starts in the stomach.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of Protein Digestion as background academic context rather than a clinical decision trigger.
Understanding the site of initial protein digestion is vital for patient care, especially for those with conditions like gastritis, peptic ulcers, or who have undergone gastric surgery (gastrectomy), as their ability to break down proteins may be compromised.
Nurses monitor patients on long-term acid-reducing medications (like Proton Pump Inhibitors) for potential nutritional deficiencies, as reduced stomach acid can impair the activation of pepsin and hinder protein digestion.
What if? If a patient has had a total gastrectomy (removal of the stomach), they will lack pepsin and hydrochloric acid. This means the initial step of protein digestion is completely bypassed, placing the full burden on the enzymes in the small intestine. These patients often require smaller, more frequent meals and may need dietary supplements.

How to Approach the Question

First, identify the keywords in the question: 'digestive juice' and 'breaks down proteins'. This points to a question about digestive physiology.
Recall the main functions of the organs listed in the options.
Consider the path of food: Mouth -> Esophagus -> Stomach -> Small Intestine -> Large Intestine.
Remember that carbohydrate digestion begins in the mouth, protein digestion begins in the stomach, and fat digestion primarily occurs in the small intestine (with help from the liver/gallbladder).
The stomach secretes pepsin, a specific enzyme for breaking down proteins. Therefore, it is the correct starting point for protein digestion.
Eliminate the other options based on their primary functions: liver (bile for fats), large intestine (water absorption), and small intestine (completes digestion, but doesn't start it).

Concept Tested & Keywords

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