Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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Transcribed Image Text:**Question:**
If proteases such as pepsin and trypsin digest protein, why do not they digest the stomach and small intestine, which are made from proteins?
**Answer Explanation:**
Proteases like pepsin and trypsin are enzymes that break down proteins into smaller peptides. Despite their ability to digest proteins, they do not harm the stomach and small intestine due to several protective mechanisms:
1. **Mucosal Barrier**: The stomach and intestines are lined with a thick layer of mucus that acts as a physical barrier, protecting the underlying tissue from the digestive action of proteases.
2. **Inactive Forms**: Proteases are often secreted in inactive forms, such as pepsinogen and trypsinogen. They become activated only in specific environments (e.g., acidic conditions in the stomach or when in contact with enterokinase in the intestine).
3. **Epithelial Renewal**: The cells of the stomach and intestinal lining are rapidly replaced, which helps maintain the integrity of the tissue despite constant exposure to digestive enzymes.
4. **Other Protective Factors**: Additional factors, such as bicarbonate secretion, neutralize acid in areas where it could cause damage.
Understanding these protective mechanisms is crucial for comprehending how the digestive system functions efficiently without self-digesting.
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