Saturday, February 19, 2005

Of Democrats, Abortion, and Human Life

Sorry for the lack of posting; I'm way behind and still trying to catch up. While I do that, here's some material you might find interesting.

Start with feministing's post Dems & Abortion: The New Republican Light? Jump to Zed's blog for a discussion on When cells become a person (make sure not to miss the comments). Then read this (lengthy) article, titled When Does Human Life Begin?:

The question of when a human life begins is a profoundly intricate one, with widespread implications, ranging from abortion rights to stem cell research and beyond. A key point in the debate rests on the way in which we choose to define the concepts of humanity, life and human life. What does it mean to be alive? What does it mean to be human? Is a zygote or an embryo alive? Is a zygote or an embryo a human being? These are intricate philosophical questions that often incite intense debate, for their answers are used as evidence in the answers to questions about the moral status of a zygote, embryo or fetus.

Unfortunately, I didn't have time to finish reading the article, but I definitely plan to. I got as far as this passage [and had some (hurried) thoughts*]:

The current Catholic Church doctrine maintains the belief that immediate animation, the instant at which the zygote is endowed with life including a soul from God, is concurrent with the moment of fertilization (Shannon and Wolter 1990).

1) Except, fertilization is not a momentary event. There is no moment of fertilization but rather a lengthy process.

Fertilization usually occurs in the [WARNING, graphic; path specimen] fallopian tube at the end closest to the ovary. It begins with contact of the sperm and the outer layer of the egg, continues with the gradual penetration of the sperm into the various layers of the egg, and is completed when the pronuclei of the sperm and egg lose their nuclear membranes and fuse to form a new cell called a zygote.

An interesting aside: The majority, up to 78%, of fertilizations do not result in live births. [Up to 60% of fertilized eggs are spontaneously aborted before they can cause a missed menstrual period. For clinically recognized pregnancies, 10-15% end in spontaneous abortion.]

That last stage of fertilization, the fusion, is called syngamy: the sperm chromosomes (23) fuse with the egg chromosomes (23) and form the zygote (46 chromosomes).

2) Also, the product of fertilization is not a cell/s designated to become a specific entity (e.g., a human), or even a particular part of an entity (e.g. an eye, or a leg). Rather, it is a bunch of distinct totipotent cells.

After syngamy, the zygote undergoes a series of divisions (preembryo stage). [About 3 days after syngamy we're at the 8 cell stage.] The newly divided cells are called blastomeres. These blastomeres are the totipotent cells. [Briefly, each one of these cells can develop independently along any line--from a preembryo to an extra-embryonic structure; they are not yet committed to a/any particular pathway.]

Another interesting aside: Once fertilization is complete, there is an entity with a new genotype. [The egg/sperm has only 23 chromosomes, but the zygote has 46--a new genotype.] However, this new entity isn't capable, at its earliest stages, of expression (transcription) of the new genotype, being regulated instead by information from the egg for continued growth and development.

3) Last, but not least, the product of fertilization doesn't have individuation. In order to be able to develop into a human person, the preembryo needs to acquire it.

From 4 to 5 days after syngamy, the blastomeres start to adhere more closely to each other, and form a morula. [During all this time, the fertilized egg has been traveling from one end of the fallopian tube towards the uterine cavity.]

Next, the morula undergoes a few changes--a central cavity appears, a distinct inner cell mass organizes--and becomes a blastocyst. The blastocyst reaches the uterine cavity where it floats around for about two more days.

After this [5-7 days after syngamy] the process of implantation begins:

As the blastocyst is in the process of attaching to the uterine wall, the cells increase in number and organize into two layers of cells. Implantation progresses as the outer cell layer of the blastocyst ... invades the uterine wall and erodes blood vessels and gland. Having begun 5 or more days after fertilization with the attachment of the blastocyst to the endometrial lining of the uterus, implantation is complete when the blastocyst is fully embedded in the endometrium several days later.

The inner cell mass is the progenitor of all the cells and cell types of the future embryo. But, at this time, these cells don't yet have the concrete potential to become a human person. They are not yet set for development as a single being.

The implanted preembryo acquires individuation about 14 days after fertilization, with the development of the primitive streak.

*ACOG's Ethics in Obstetrics and Gynecology [2002;70-4] is the reference. I tried to adapt most of the material, but I couldn't eliminate the medspeak entirely. So I included the glossary; hope it helps.


Blastocyst: A sphere of cells containing a fluid-filled cavity forming about 4 days after fertilization and prior to the beginning of implantation.

Blastomeres: The cells derived from the first and subsequent cell division of the zygote.

Diploid (in humans, 46): A cell having two chromosome sets, usually one maternal and one paternal, twice the haploid number.

Embryo: The stage in human development starting from about 2 weeks after fertilization, with organization around a single primitive streak [band of cells], and continuing until the end of the 8th week after fertilization when all the major structures are represented.

Fertilization: The process which renders gametes capable of further development; it begins when sperm contacts the plasma membrane of the egg and ends with the formation of the zygote.

Gametes: Mature reproductive cells, usually haploid in chromosome number [ovum (egg) or sperm].

Haploid: The chromosome number of a normal gamete [egg or sperm]. In humans, the haploid number is 23, representing one member of each chromosome pair. [Egg (23) + Sperm (23) = Diploid cell (46)].

Implantation: Attachment of the blastocyst to the endometrium [uterine lining] and subsequent embedding in the endometrium. Implantation begins at about 5-7 days after fertilization and may be completed as early as 8-9 days after fertilization.

Inner cell mass: The centrally located cells within the blastocyst; these cells will develop into the embryo.

Morula: A compact sphere of 16 blastomeres that forms at about 3-4 days after fertilization.

Oocyte: An immature female reproductive cell, one that has not completed the maturing process to form an ovum (gamete).

Preembryo: The developing cells produced by the division of the zygote until the formation of the embryo proper at the appearance of the primitive streak [band of cells] about 14 days after fertilization.

Primitive streak: The initial band of cells from which the embryo begins to develop. The primitive streak is present at about 15 days after fertilization.

Pronuclei: The egg and sperm nuclei after penetration of the sperm into the egg during fertilization.

Spermatozoa: Mature male germ cells (gametes).

Syngamy: The final stage of the fertilization process in which the haploid (23) chromosome sets from the male and female gametes come together following breakdown of the pronuclear membranes to form the zygote.

Totipotent: Able to differentiate along any line; the capacity of a cell or group of cells to produce all of the products of conception--the extra-embryonic membrane and tissue, the embryo, and, subsequently, the fetus.

Transcription: Transfer of genetic code information from one kind of nucleic acid to another.

Zygote: The single cell formed by the union of the male and female haploid (23) gametes at syngamy.


At 6:06 PM, Blogger Dr. Charles said...

a very good review, as always.
just wanted to alert you to this post, don't feel pressured to respond to it, but i figured you'd at least like to listen to the report on NPR:

Have a great weekend!


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