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

18. The Heart

Cardiac Cycle

Anatomy & Physiology

18. The Heart

Cardiac Cycle

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Multiple Choice

Which event in the cardiac cycle is most directly responsible for producing the first heart sound (S1)?

Opening of the semilunar valves

Atrial contraction

Closure of the atrioventricular (AV) valves

Closure of the semilunar valves

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Verified step by step guidance

Understand the cardiac cycle: The cardiac cycle consists of systole (contraction phase) and diastole (relaxation phase). During systole, blood is ejected from the heart chambers, while diastole allows the chambers to fill with blood.

Identify the heart sounds: The first heart sound (S1) is caused by the closure of the atrioventricular (AV) valves (mitral and tricuspid valves), while the second heart sound (S2) is caused by the closure of the semilunar valves (aortic and pulmonary valves).

Relate S1 to valve closure: During ventricular systole, the pressure in the ventricles rises, causing the AV valves to close. This prevents backflow of blood into the atria and produces the S1 sound, often described as a 'lub' sound.

Eliminate incorrect options: Opening of the semilunar valves and atrial contraction do not produce heart sounds. Closure of the semilunar valves produces the second heart sound (S2), not S1.

Conclude the correct event: The closure of the AV valves is the event most directly responsible for producing the first heart sound (S1). This occurs at the beginning of ventricular systole.