Wikipedia:Reference desk/Archives/Science/2020 December 18

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December 18

What triggers the hormones that induce labor?

In a scenario where both the baby and the mother are healthy, how does the body knows that's time to give birth? What triggers the hormones like prostaglandin or oxytocin (or any other hormones involved)? --Bumptump (talk) 01:46, 18 December 2020 (UTC)

Quote: "Oxytocin receptors are probably crucial for the onset of human labor, and the stimulus for the increase in uterine prostaglandins may be oxytocin originating from the fetus."^[1] Which raises the question, how does the fetus know it's time to become a baby?  --Lambiam 07:45, 18 December 2020 (UTC)

Corticotropin-releasing hormone (CRH) and cortisol are released by the fetus (and the uterus) when it begins to feel mechanical stress from the pressure of being too large for the uterus. Next the mother produces estriol, which inhibits the synthesis of progesterone, which was inhibiting contractions. Abductive (reasoning) 11:43, 18 December 2020 (UTC)

To add to this, fetal stress (which can occur from growth restriction) stimulates placental CRH production. This promotes prostaglandin release in the decidua and myometrium. Placenta-derived estradiol levels have been increasing throughout pregnancy due to greater contributions of estrogen precursors from the fetal adrenals, while cortisol from elevated CRH competes against progesterone for glucocorticoid receptor binding and myometrial progesterone receptor withdrawal serve to increase the functional ratio between estradiol and progesterone. This high ratio promotes formation of gap-junctions in the myometrium, leading to enhanced myometrial contractility and responsiveness to oxytocin and prostaglandins. Additionally, relaxin has been stimulating cervical hyaluronan synthesis and increasing collagen solubility to facilitate cervical ripening, so contractions are better able to induce parturition. JoelleJay (talk) 22:19, 18 December 2020 (UTC)

Why large flags don't fly as much as small ones

I see many times, that large flags tend to stay put, and not fly, while small flags are much less likely to not fly. An explanation which is related to cubic square law can't apply, as the thickness of a flag is constant. The air resistance of a flag is proportional to its area, which again is proportional to its mass. Therefore, large and small flags should fly alike. My question why it is not the case in reallity? --Exx8 (talk) 13:32, 18 December 2020 (UTC)

Because they're heavier. First of all, the thickness is not necessarily constant; larger flags will normally be made of stronger material. Secondly, the area is not relevant if a flag is simply hanging down and not flying. Larger flags will also absorb more moisture.--Shantavira|^{feed me} 14:17, 18 December 2020 (UTC)

The square–cube law might apply at least to some part. 85.76.79.191 (talk) 18:23, 18 December 2020 (UTC)

Vas deferens sheath removal question

Is the sheath of the vas deferens ever removed either in part or in full? Futurist110 (talk) 21:23, 18 December 2020 (UTC)

Would it make a vas difference? Sagittarian Milky Way (talk) 00:53, 19 December 2020 (UTC)

Not sure. I wonder if recanalization/regeneration of the vas deferens would still be possible without the sheath. Probably Yes, I suspect--unfortunately. :( Futurist110 (talk) 01:22, 19 December 2020 (UTC)