(no subject)

[kcobweb]

Kicky kicky kick!

Geez. I have gone from "I only feel movement occasionally, when I'm really concentrating and focusing" one week ago to constant karate practice. Amazing. She is most active - as has been true all along - when I first lay down to go to sleep and when I first wake up in the morning. And between 11 a.m. and noon, oddly enough.

Other things no one ever tells you about pregnancy: how your belly button changes. It's bizarre. (I don't have an outie yet. It's just getting... shallower. And tender.)

Which then gets me thinking about how truly utterly weird it is that I used to be attached there to an umbilical cord which was my only source for nourishment, etc. - and they just cut it off and left this little... useless vestigial pucker on my belly. Does anyone else think that's a weird concept?

Comments

[journeywoman.livejournal.com]

I was curious about the fate of my umbilical cord on the inside, so I got out Gray's Anatomy and looked it up. Turns out that the umbilical cord is only an intermediate function for that structure in the grand scheme of things. It starts off as an embryonic structure, and gradually changes into a major blood vessel or two. Then when the placenta is developed it turns into the umbilical cord, and in the two or three weeks after delivery, it evolves into a ligament on your liver.

Other parts of the embryo have similar multiple functions. It's really pretty neat how good the body is at recycling organs and other structures.

[kcobweb.livejournal.com]

Excellent - that is precisely what I was looking for! The transition from your-major-source-for-all-things to nothing? just didn't make sense - those structures for nutrient-etc.-delivery would have to go somewhere.

The other embryology question that has fascinated me in the past is the transition between fetal breathing and infant breathing. Fetal breathing involves liquid: the fetal lungs extract oxygen from the amniotic fluid. When you are born, that first cry you make draws the air into the lungs and inflates them - and bingo! you're breathing gases instead of liquids. But how does that change-over really work? I went through a bunch of neonatal/maternal care nursing textbooks, and found nothing that satisfied my curiosity. I understand how it happens before and after - I want to understand the mid-point too. I was thinking about this because premature babies often have lungs that are not developed enough to breathe air yet, so they need supplemental oxygen.

Embryology is so fascinating. I should take/have taken a course in it at some point, except that academically speaking I'm totally allergic to science coursework.

[journeywoman.livejournal.com]

I've heard that swallowing amniotic fluid helps lung development, but I've always sort of assumed that the fetus got oxygen through the umbilical cord. After all, it still gets oxygen during delivery, when it's no longer in its bag of waters. Hm.

So I consulted Gray's Anatomy again. (It's a little disturbing to realize that it was first published in the 1850s and yet is still so accurate, considering they didn't have x-rays or MRIs back then.) It was mostly silent on the fetal oxygenation issue. It did mention as a casual aside that the fetal lungs weren't used till after birth, but I can't remember the exact wording. But it's old and maybe they've discovered new things since it was last updated.

Embryology would be just an amazing field of study. I can't believe that something as complicated as a human being--or any vertebrate, really--can get produced with so few errors (in the scheme of things).

[kcobweb.livejournal.com]

It also has to do with the development in the lungs of surfactant, which is critical for alveolar stability (starts production at weeks 20-24).

My nursing textbook here (Essentials of Maternal-Newborn Nursing, 1990) says the following:

The ability of the neonate to breathe air immediately upon exposure to extrauterine life appears to be the consequence of weeks of intrauterine practice. Fetal breathing movements (FBM) occur as early as 11 weeks' gestation. Goldstein and Reid (1980) propose that FBM are essential for development of chest wall muscles (including the disphragm) and to a lesser extent for regulating lung fluid volume and therefore lung growth.

It goes on to say that the first breath expands the alveoli. Then:

An important chemical stimulator that contributes to the onset of breathing is transitory asphyxia of the fetus and newborn. Elevation in PCO2 and decrease in pH and PO2 are the natural outcome of normal vaginal birth with cessation of placental gas exchange and umbilical cord pulsation, and cutting of the cord. These changes, which are present in all newborns to some degree, stimulate the aortic and carotid chemoreceptors, initiating impulses that trigger the medulla's respiratory center.

It then goes on to say that the temperature changes (from 98.6F to 70-75F) are another stimulus. And that secretion of fetal lung fluid diminshes 48 hours before onset of labor. As it passes through the birth canal, a lot of the remainder is squeezed out. And as the chest wall is born, there is a recoil, which automatically sucks some air into the lungs, which helps start the process.