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

The Stomach

Anatomy & Physiology

23. The Digestive System

The Stomach

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2:38 minutes

Problem 14

Textbook Question

Trace the path of a single protein molecule that has been ingested.
The protein molecule will be digested by enzymes made by
a. The mouth, stomach, and colon
b. The stomach, liver, and small intestine
c. The small intestine, mouth, and liver
d. The pancreas, stomach, and small intestine

Verified step by step guidance

Step 1: Begin by understanding that proteins are large macromolecules that need to be broken down into smaller units (amino acids) for absorption. This process involves mechanical digestion and enzymatic breakdown. The journey starts in the mouth, where mechanical digestion occurs through chewing, but enzymatic digestion of proteins does not begin here.

Step 2: Next, trace the protein molecule to the stomach. In the stomach, enzymatic digestion begins. The stomach secretes hydrochloric acid (HCl), which denatures proteins, and pepsinogen, which is activated into pepsin by HCl. Pepsin is the enzyme responsible for breaking proteins into smaller polypeptides.

Step 3: After the stomach, the partially digested protein moves into the small intestine. Here, the pancreas plays a crucial role by secreting digestive enzymes like trypsin and chymotrypsin into the small intestine. These enzymes further break down polypeptides into smaller peptides and eventually into amino acids.

Step 4: The small intestine also produces enzymes like peptidases that complete the breakdown of peptides into individual amino acids. These amino acids are then absorbed through the intestinal lining into the bloodstream for distribution to the body's cells.

Step 5: Clarify that the colon (large intestine) is not involved in protein digestion. Its primary role is water absorption and the formation of feces. Therefore, the correct organs involved in protein digestion are the stomach, pancreas, and small intestine.

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Key Concepts

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

Protein Digestion

Protein digestion begins in the stomach, where gastric juices, including hydrochloric acid and pepsin, break down proteins into smaller peptides. This process continues in the small intestine, where enzymes from the pancreas, such as trypsin and chymotrypsin, further digest peptides into amino acids, which can then be absorbed into the bloodstream.

Role of Digestive Organs

Different organs play specific roles in digestion. The stomach is primarily responsible for the initial breakdown of proteins, while the pancreas produces digestive enzymes that are released into the small intestine. The liver also contributes by producing bile, which aids in the digestion and absorption of fats, although it does not directly digest proteins.

Absorption of Nutrients

After proteins are broken down into amino acids in the small intestine, these nutrients are absorbed through the intestinal walls into the bloodstream. This absorption is facilitated by the villi and microvilli, which increase the surface area for nutrient uptake, ensuring that the body can utilize the amino acids for various functions, including tissue repair and enzyme production.

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Related Practice

Textbook Question

Describe the regulation of the cephalic, gastric, and intestinal phases of gastric secretion.

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Multiple Choice

Proton Pump Inhibitors (or PPIs) are some of the widely used drugs in the world and are prescribed for chronic heartburn/acid reflux. They work by inhibiting the movement of H⁺ ions across the membrane into the gastric juice, thereby lowering the concentration of HCl. As described, which cell of the gastric glands would you expect PPIs to affect?

More than one choice may apply.

Where in the stomach do the strongest peristaltic waves occur?

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Multiple Choice

The only stomach function that is essential to life is __________.

A surgical procedure known as gastric bypass involves removing all or part of the stomach.

How would stomach removal affect absorption of vitamin B12? Explain.

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Multiple Choice

Which of the following products does the stomach produce?

Troy Francis, a middle-aged salesman, complains of a burning pain in the 'pit of his stomach,' usually beginning about two hours after eating and abating after drinking a glass of milk. When asked to indicate the site, he points to his epigastric region. The GI tract is examined by X-ray fluoroscopy. A gastric ulcer is visualized, and drug therapy using a proton pump inhibitor and antibiotics is recommended.

a. Why is this treatment suggested?

b. What are the possible consequences of nontreatment?

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Multiple Choice

The phases of gastric secretion, from first to last, are __________.