enter image description hereI just have a quick question regarding what my textbook says. I have tried searching online but I have failed to find an answer. Basically, my textbook states that arterioles are smaller in diameter compared to arteries but have a larger lumen. Isn't the diameter measured across the lumen? So how can the artery have a smaller lumen but be larger in diameter?

Thank you

  • $\begingroup$ Do you have the exact quote in context from the textbook? You are right, that makes no sense at all and is false, the lumen of arteries is larger than the lumen of arterioles. It's possible they are referring to the ratio of the lumen to the overall diameter, but even in that case I'd be uncertain of the statement and my intuition is that it is still false. $\endgroup$ – Bryan Krause Oct 18 '18 at 20:09
  • $\begingroup$ I have added a photo showing what the textbook states. Thank you for your reply :) $\endgroup$ – James Oct 18 '18 at 20:15
  • $\begingroup$ The photo shows that the book states that arterioles have a larger muscle layer and lumen. Is this correct? $\endgroup$ – James Oct 18 '18 at 20:16

The key word you are missing is "relatively": I'm not clear what they mean "relatively" to based on where you cut off the passage, but they probably mean relative to the entire diameter of the vessel; the statement is probably not true for area but you would have to choose a particular artery and arteriole to compare, and both categories have a lot of variation in size within and between organisms.

Arterioles do have a "relatively" thicker muscle layer than the great arteries because they are the place where most of the contraction takes place that regulates the resistance of different vascular beds. Because of that, though, their lumen size varies quite a bit depending on the state of the muscle. When the smooth muscle in the vessel wall is relaxed, arterioles are much larger than when contracted. Even if the book is correct that according to whatever measure of "relative" they are using, arterioles have a wider lumen, I have a hard time believing this would be true over the entire range of contraction.

  • $\begingroup$ I will attach entire passage $\endgroup$ – James Oct 18 '18 at 20:22
  • $\begingroup$ Thank you for your answer. I understand the muscle layer part but I still don't know what I should write if an exam question was to come up. Should I write that the arterioles have a smaller or larger lumen? $\endgroup$ – James Oct 18 '18 at 20:26
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    $\begingroup$ Arterioles have a smaller lumen than arteries. The "ioles" at the end implies they are "little arteries." If I were you I would focus on the differences in function in your studying. $\endgroup$ – Bryan Krause Oct 18 '18 at 20:37

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