The correct option is
A. absorption of glucose.
Detailed Explanation:
- Understanding the Functions of the Stomach:
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The mammalian stomach is primarily involved in the digestion of food. It performs several key functions, including:
- Secretion of Hydrochloric Acid (Option B): The stomach lining contains parietal cells that secrete hydrochloric acid (HCl). This acid creates an acidic environment (pH 1.5 to 3.5) that helps in breaking down food and activating digestive enzymes.
- Secretion of Gastric Juice (Option C): Gastric juice is a mixture of hydrochloric acid, pepsinogen (an inactive enzyme that is activated to pepsin in the acidic environment), and mucus. This juice is crucial for protein digestion and protecting the stomach lining from its own acid.
- Churning of Food (Option D): The stomach has muscular walls that contract to mix and churn the food with gastric juices, turning it into a semi-liquid substance called chyme. This mechanical digestion is essential for effective chemical digestion.
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Absorption of Glucose (Option A):
- The stomach is not involved in the absorption of glucose. While it does absorb some substances (like alcohol and certain medications), the primary site for glucose absorption is the small intestine, specifically the jejunum and ileum. Here, glucose is absorbed through the intestinal walls into the bloodstream via specialized transport mechanisms (like SGLT1, a sodium-glucose co-transporter).
Why Other Options Are Incorrect or Weaker:
- Option B: Secretion of Hydrochloric Acid:
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This is a fundamental function of the stomach. The secretion of HCl is essential for creating the acidic environment necessary for enzyme activity and food breakdown. Therefore, this option is correct regarding the functions of the stomach.
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Option C: Secretion of Gastric Juice:
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Gastric juice is vital for digestion in the stomach. It contains enzymes and acid that facilitate the breakdown of proteins and kill pathogens. This is another correct function of the stomach.
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Option D: Churning of Food:
- The mechanical action of churning food is a critical function of the stomach. It ensures that food is mixed thoroughly with gastric juices, promoting effective digestion. This option is also correct.
Summary of Key Points:
- The mammalian stomach is involved in the secretion of hydrochloric acid, gastric juice, and the mechanical churning of food.
- The stomach does not absorb glucose; this occurs primarily in the small intestine.
- Understanding the specific functions of the stomach helps clarify its role in the digestive system and distinguishes it from other parts of the gastrointestinal tract.
Revision Summary:
- The stomach secretes hydrochloric acid and gastric juice, and it churns food.
- Glucose absorption occurs in the small intestine, not the stomach.
- The stomach's acidic environment is crucial for protein digestion.
- Recognizing the distinct roles of different digestive organs is essential for understanding human physiology.