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Difficulty: MediumHuman Anatomy and Body Systems

In the human circulatory system, blood returning from the lower extremities to the heart travels under relatively low pressure against gravity. Which anatomical structure within veins prevents the retrograde backflow of blood?

  1. A
    Thick concentric layers of smooth muscle that sustain high systolic pressure
  2. B
    Highly elastic connective tissue laminae that maintain continuous rebound pressure
  3. One-way pocket valves formed by folds of the endothelial liningAnswer
  4. D
    Narrow, high-resistance lumens lined with semipermeable fenestrations

Answer

One-way pocket valves formed by folds of the endothelial lining
The correct answer identifies one-way pocket valves formed by the tunica intima endothelium. Because venous pressure is significantly lower than arterial pressure, these unidirectional cusps ensure that blood moved upward by skeletal muscle contraction cannot slip backward between contractions.

Step-by-Step Solution

1
Analyze the physiological challenge presented in the stem
Blood in the venous system operates under low hydrostatic pressure and must overcome gravitational force to return to the right atrium of the heart.
Identifying the pressure regime and direction of transport establishes which structural adaptations are necessary.
2
Evaluate anatomical adaptations of veins versus arteries
Veins possess wide lumens, thinner walls, and specialized endothelial flap valves that open toward the heart and seal shut when blood starts to flow backward.
Arteries rely on thick muscular walls and elastic recoil to propel blood under high pressure, whereas peripheral veins rely on one-way valves paired with skeletal muscle pumps.

Key Concept

Venous valve function and low-pressure circulatory return in human anatomy
Estimated Time:1m 0s
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Topics

Human Anatomy and Body Systems

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