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

21. The Immune System

Introduction to First-Line Defenses

Anatomy & Physiology

21. The Immune System

Introduction to First-Line Defenses

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Multiple Choice

Which portal of entry is the most commonly used by pathogens in the human body?

Skin

Gastrointestinal tract

Respiratory tract

Urogenital tract

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Verified step by step guidance

Understand the concept of 'portal of entry': It refers to the site through which pathogens enter the host's body. Common portals include the skin, respiratory tract, gastrointestinal tract, and urogenital tract.

Consider the respiratory tract: This is a major portal of entry because it is constantly exposed to the external environment through breathing, making it a common route for airborne pathogens.

Evaluate the skin as a portal of entry: While the skin is a barrier, it is less commonly used by pathogens unless there are cuts or abrasions.

Assess the gastrointestinal tract: This portal is used by pathogens that are ingested, but it is protected by stomach acid and enzymes.

Examine the urogenital tract: This is a specific portal for sexually transmitted infections, but it is not as commonly used as the respiratory tract for general pathogens.