Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

23. The Digestive System

Introduction to the Digestive System

Anatomy & Physiology

23. The Digestive System

Introduction to the Digestive System

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Problem 24

Textbook Question

A drop in pH below 4.5 in the duodenum stimulates the secretion of
(a) Secretin
(b) Cholecystokinin
(c) Gastrin
(d) All of these

Verified step by step guidance

Understand the physiological context: The duodenum is the first part of the small intestine, and its pH is regulated to ensure proper digestion and enzyme activity. A drop in pH below 4.5 indicates increased acidity, which triggers specific hormonal responses to protect the duodenum and regulate digestive processes.

Identify the role of secretin: Secretin is a hormone released by the duodenum in response to acidic chyme (low pH). Its primary function is to stimulate the pancreas to release bicarbonate-rich fluid, which neutralizes the acidity and raises the pH.

Consider the role of cholecystokinin (CCK): Cholecystokinin is secreted by the duodenum in response to the presence of fats and proteins, not directly due to low pH. Its main function is to stimulate the release of bile from the gallbladder and pancreatic enzymes, aiding in digestion.

Evaluate the role of gastrin: Gastrin is a hormone secreted by the stomach that stimulates acid production. It is not directly involved in responding to low pH in the duodenum; instead, it promotes acid secretion in the stomach.

Determine the correct answer: Based on the physiological roles of the hormones, secretin is the primary hormone stimulated by a drop in pH below 4.5 in the duodenum. The other options (cholecystokinin and gastrin) are not directly triggered by low pH in this context.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

pH Regulation in the Duodenum

The duodenum, the first part of the small intestine, plays a crucial role in digestion and requires a specific pH range for optimal enzyme activity. A drop in pH below 4.5 indicates increased acidity, which can harm intestinal lining and disrupt digestive processes. This triggers physiological responses to restore a more neutral pH.

Secretin

Secretin is a hormone produced by the S cells in the duodenum in response to acidic chyme. Its primary function is to stimulate the pancreas to release bicarbonate, which neutralizes stomach acid, and to inhibit gastric acid secretion. This helps maintain the appropriate pH for digestive enzymes to function effectively.

Cholecystokinin (CCK)

Cholecystokinin is a hormone released by the I cells in the duodenum in response to fatty acids and amino acids. While its primary role is to stimulate gallbladder contraction and pancreatic enzyme secretion, it also plays a part in regulating gastric emptying and promoting satiety. CCK's release can be influenced by changes in pH, but it is not directly stimulated by low pH.

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Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

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Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

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Multiple Choice

The enteric nervous system is the in-house nerve supply of the alimentary canal.

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Textbook Question

Make a simple line drawing of the organs of the alimentary canal and label each organ. Then add three labels to your drawing—salivary glands, liver, and pancreas—and use arrows to show where each of these organs empties its secretions into the alimentary canal.

The myenteric nerve plexus is located in which tunic of the alimentary canal?

Double sheets of peritoneum that provide support and stability for the organs of the peritoneal cavity are the

(a) Mediastina

(b) Mucous membranes