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Pulses and Pressures Quiz
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Which statement best describes fully developed laminar blood flow in an idealised straight artery?
- A Blood reverses direction intermittently during each cardiac cycle You picked ✕
- B Blood flow becomes disorganised immediately after leaving the heart You picked ✕
- C Blood moves in parallel layers with the highest velocity in the centre of the vessel You picked ✓
- D Blood flows chaotically with frequent changes in direction due to high resistance You picked ✕
- E Blood moves at the same velocity across the entire vessel lumen You picked ✕
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Incorrect
The answer is C: Blood moves in parallel layers with the highest velocity in the centre of the vessel
Explanation
Why C is correct
See Types of Blood Flow. Option C is correct. Blood normally flows in the laminar pattern: it moves in smooth, orderly layers (laminae) that run parallel to the vessel wall and do not mix, like sheets sliding over one another. The layer in contact with the vessel wall is slowed by friction against the wall, and each layer inside it is slowed less, so the layer in the centre of the lumen moves fastest. If you plot the speed across the vessel, it makes a curved, parabolic profile, with the maximum in the middle. Laminar flow is efficient and silent, because little energy is wasted, and it is the normal pattern in healthy, straight, unobstructed arteries. It is different from turbulent flow, in which the blood swirls and mixes chaotically. Turbulence occurs when the vessel is narrowed or rough, when the flow is fast, or at branches, and it wastes energy, increases resistance and makes noise. A good picture is a smooth river with a fast middle and slow banks, compared with white water over rocks.
- Pattern: Blood moves in smooth parallel layers that do not mix.
- Velocity: The layer touching the wall is slowed by friction and the central layer moves fastest, giving a parabolic profile.
- Setting: Laminar flow is silent and is the normal pattern in healthy, straight, unobstructed arteries.
Why the other options are incorrect
- A. Blood reverses direction intermittently during each cardiac cycle: Flow that reverses direction in each cardiac cycle is not a feature of normal laminar arterial flow. In an artery, blood moves forward in pulses. Reversal of flow points to an abnormal state, such as a leaking aortic valve. Your answer
- B. Blood flow becomes disorganised immediately after leaving the heart: Blood does not become chaotic just because it leaves the heart. In a healthy, unobstructed artery the flow stays laminar. Turbulence appears when there is narrowing or irregularity. Your answer
- D. Blood flows chaotically with frequent changes in direction due to high resistance: Chaotic movement with changing direction describes turbulent flow, which occurs when the vessel is narrowed or irregular or the flow is very fast. Laminar flow is smooth and orderly. This option describes the pattern that causes a bruit. Your answer
- E. Blood moves at the same velocity across the entire vessel lumen: If blood moved at the same speed across the whole lumen, no friction against the wall would slow it. In reality the layer touching the wall is slowed by friction and the centre moves fastest, giving different speeds across the vessel. Your answer
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More questions from this set. Start the quiz to answer them and see each explanation.
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1
Which statement best defines pulse pressure?
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2
An adult at a normal resting heart rate has a blood pressure of 120/60 mmHg. Using the standard resting approximation, what is the estimated mean arterial pressure?
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