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 of the following is not a portal of entry for pathogens?

Respiratory tract

Gastrointestinal tract

Lymph nodes

Skin

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Verified step by step guidance

Understand the concept of 'portal of entry': A portal of entry is a site through which pathogens enter the body. Common portals include mucous membranes, skin, and parenteral routes.

Identify the common portals of entry: The respiratory tract and gastrointestinal tract are typical portals of entry for pathogens, as they are exposed to the external environment and have mucous membranes.

Consider the skin: The skin is a barrier to pathogens, but it can become a portal of entry if there are cuts, abrasions, or punctures.

Evaluate the lymph nodes: Lymph nodes are part of the immune system and are not exposed to the external environment. They do not serve as a portal of entry for pathogens.

Conclude which option is not a portal of entry: Based on the understanding that lymph nodes are internal and part of the immune system, they are not a portal of entry for pathogens.