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

Physical Barriers in First-Line Defenses: Skin

Anatomy & Physiology

21. The Immune System

Physical Barriers in First-Line Defenses: Skin

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Multiple Choice

What is the most extensive physical barrier that prevents foreign substances from entering the body?

Mucous membranes

Tears

Skin

Cilia

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Verified step by step guidance

Begin by understanding the role of physical barriers in the body's defense system. These barriers are the first line of defense against pathogens and foreign substances.

Consider the various physical barriers listed: mucous membranes, tears, skin, and cilia. Each has a specific function in protecting the body.

Mucous membranes line various cavities in the body and secrete mucus, which traps pathogens and particles.

Tears help to wash away foreign particles from the eyes, providing a protective mechanism.

Skin is the largest organ of the body and covers the entire external surface, providing a comprehensive barrier against pathogens. It is composed of multiple layers that prevent the entry of foreign substances.

Cilia are hair-like structures that line the respiratory tract and help to move mucus and trapped particles out of the airways. While they are effective in their specific location, they do not cover as extensive an area as the skin.