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

19. The Blood Vessels

Capillaries

Anatomy & Physiology

19. The Blood Vessels

Capillaries

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1:57 minutes

Problem 9

Textbook Question

Blood flow in the capillaries is steady despite the rhythmic pumping of the heart because of the:
a. Elasticity of the large arteries
b. Small diameter of capillaries
c. Thin walls of the veins
d. Venous valves

Verified step by step guidance

Understand the problem: The question asks why blood flow in the capillaries remains steady despite the rhythmic pumping of the heart. This requires knowledge of the cardiovascular system, particularly the role of arteries, capillaries, veins, and their structural features.

Review the options: Each option refers to a specific anatomical or physiological feature. For example, the elasticity of large arteries (a) relates to their ability to stretch and recoil, the small diameter of capillaries (b) affects resistance and flow, thin walls of veins (c) relate to their function in returning blood to the heart, and venous valves (d) prevent backflow in veins.

Focus on the key concept: Blood flow in capillaries is steady because of a mechanism that dampens the pulsatile nature of blood flow caused by the heart's rhythmic pumping. This mechanism is primarily related to the properties of arteries, not capillaries or veins.

Analyze the role of large arteries: Large arteries, such as the aorta, have elastic walls that stretch during systole (when the heart pumps blood) and recoil during diastole (when the heart relaxes). This elasticity helps to convert the pulsatile flow from the heart into a more continuous flow, which is crucial for steady blood flow in capillaries.

Eliminate incorrect options: The small diameter of capillaries (b) increases resistance but does not directly explain the steadiness of flow. Thin walls of veins (c) and venous valves (d) are related to venous return, not capillary flow. Therefore, the correct answer is related to the elasticity of large arteries (a).

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Key Concepts

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

Elasticity of Large Arteries

The elasticity of large arteries allows them to expand and contract with each heartbeat, which helps to absorb the pressure generated by the heart's pumping action. This elasticity ensures that blood flow remains continuous and smooth, preventing sudden spikes in pressure that could disrupt circulation in smaller vessels like capillaries.

Capillary Diameter

Capillaries have a very small diameter, often just wide enough for red blood cells to pass through in single file. This narrowness increases resistance to blood flow, which helps to maintain a steady flow rate despite the pulsatile nature of blood being pumped from the heart, allowing for efficient nutrient and gas exchange.

Venous Valves

Venous valves are structures within veins that prevent the backflow of blood, ensuring that it moves in one direction toward the heart. These valves are particularly important in the limbs, where blood must travel against gravity, and they contribute to the steady return of blood to the heart, complementing the steady flow in capillaries.