Form and Function

For many years women were told that they should not breastfeed while taking medications. But today, with consideration for the risks of not breastfeeding as well as information provided by the study of transfer of medications from mother to baby, most women are able to safely combine medications and breastfeeding.

There are multiple factors that determine infant exposure to medications through breastmilk. Some of the factors that occur at the site of the milk production cells are described below:

1. Mother's stage of lactation. In the early days of breastfeeding, the specialized epithelial cells that produce milk (i.e. lactocytes) are small and unjoined, allowing free intercellular transfer of medications from the mother's plasma to the milk. However, because total amounts of available milk are small during this time, total transfer to the baby is lessened. Between 3 and 5 days postpartum, as milk production increases, the lactocytes increase in size and form tight junctions, and all further transfer must occur transcellularly, primarily through passive diffusion.

2. Maternal plasma concentration of the drug. As maternal plasma concentration increases, the drug moves through the lactocyte and into the milk along its concentration gradient, with maximum transfer occurring when levels peak in the maternal plasma. As the mother's body metabolizes the medication and plasma concentration levels fall below milk concentration levels, many drugs will pass back into the mother's blood.

3. Molecular weight of the drug. Transcellular diffusion requires that the drug compound pass through the cell membrane of the lactocyte, a process that is more difficult for larger molecules or molecules that are not protein bound and therefore less lipid soluble. At molecular weights greater than 500 daltons, diffusion through the cell becomes more difficult, and drugs with molecular weights greater than 1000 daltons do not pass in clinically significant amounts. One very common medication, insulin, falls into this category.

Resources

Thomas Hale, Chapter 5: Drug Therapy and Breastfeeding in Breastfeeding and Human Lactation, edited by Jan Riordan.

Here are my results from the VARK questionnaire:

Visual: 4
Aural: 2
Read/Write: 8
Kinesthetic: 2

The only surprise for me was that I did not know that there was a learning style scheme that included a read/write component. I'd only previously heard of the visual/auditory/kinesthetic system. Of those 3, I would certainly have pegged myself as a visual learner, which is supported by the VARK results, but with the read/write component included, I had no doubt that that would be my strongest learning style. I've always been a big reader and continue to do most of my professional continuing education through reading and writing. I've never been one to re-write class notes, but flashcards and repeatedly re-reading notes have always been staple study techniques for me when large measures of memorization are involved. I think most academic study is geared to a read/write learning style which is to my advantage.

(I included the famous quote that ends with "form ever follows function" in the header of this blog. I've frequently heard "form follows function" in reference to evolution and if forced to guess, might have attributed the quote to Darwin. Turns out the phrase was made famous by renowned late 19th/early 20th Century architect Louis Sullivan. Who knew?)

I'm working on the endless task of decluttering our household, and today I was making some hard decisions about which books to keep ("All of them!" my mind screams) and which to donate to the library. One that made the cut to keep was The Beak of the Finch by Jonathan Weiner. It follows the work of Peter and Rosemary Grant on the subject of natural selection within Darwin's finches (specifically the ground finches, genus Geospiza) in the Galapagos. Their findings on speciation and genetic variability over short time frames have more to do with the study of evolution than anatomy or physiology, but the relationship between beak size/shape and food sources are a perfect example of the relationship between form and function.


1. Geospiza magnirostris - Large ground finch - large "crushing-type" beak, feeds on large seeds
2. Geospiza fortis - Medium ground finch - smaller "crushing-type" beak, feeds on smaller seeds
3. Geospiza (now Camarhynchus) parvula - Small tree finch, small and narrow beak, feeds on insects
4. Certhidea olivacea - Warbler finch - long and narrow beak, feeds on insects

The thick and powerful beaks of the ground finches are perfect for crushing the hard exterior of seeds in order to access the edible fruits within. And the longer and narrower beak of the tree and warbler finches are suited to picking insects from crevices where they may hide.

* There is a great drawing of adaptive radiation amongst the finches here.
* There is a nice summary of the Grants' work here.

First things first, my introduction. I graduated in 1997 with a B.S. in Animal Ecology from Iowa State University. I worked for the U.S. Forest Service doing GIS (Geographic Information Systems) work and a tiny bit of field work and wildland firefighting from 1997-2001, first in Minnesota, then here in Colorado. I moved to Fort Collins in 1999 to start a Master's at CSU in remote sensing and GIS, but after finishing all my coursework and with my thesis staring me in the face, I had something of a career crisis and began considering moving into a different line of work. My thesis languished for several years until I finally committed to not finishing my degree, and in the mean time I trained and began working as a doula (professional labor and birth support person). I continue to work as a doula today and now also teach a childbirth preparation series called Hypnobabies and breastfeeding classes as well. I have been with my husband Matt for 6 years and do not have children.

As for why I'm taking A&P, that's an excellent question that frankly I'm still asking myself. As much as I love working in the childbirth field, every so often I give some hard thought to the irregular work and low-paying nature of the job. Recently I looked into what it would take for me to become a nurse through the UNC second degree program, and A&P is the first step in that process. So for the moment I am starting to work my way through the prerequisites and will make a final decision about pursuing nursing, or perhaps midwifery, on down the line.

My greatest strength and greatest weakness as a student are probably the same: I have already spent a lot of time as a student. I am willing and able to do my work, study, I generally get good grades, etc. No mysteries there. But it is definitely weird to be going back to undergraduate classes after spending 3 years in graduate school and having left my early 20's far behind. And general chemistry and biology were are looooong time ago, so I'm glad we're doing a review.