by DipsyTipsy on Tue Aug 01, 2006 11:38 am
About 1 month before conception: Almost all adult males produce thousands of spermatozoa (male germ cells) each second. It would take about 500 of them lined up in a row to total 1 inch in length. They take a month or so to travel from a testicle, through a long tube called the "vas deferens," to reach a small reservoir inside the man's prostate gland. Here, semen (a mixture of spermatozoa and various fluids) is formed. Each spermatozoon contains human DNA. They certainly appear to be living organisms. As seen in a microscope, they seem to be moving energetically with the sole motivation of fusing with an ovum. Most people consider them to be a form of human life, because they appear alive and contain human DNA. Some scientists define "life" so strictly that spermatozoon are not considered alive. Its movements are due to chemical reactions.
Perhaps one day before conception: The woman ovulates and produces one mature ovum (egg cell). It travels down one of her fallopian tubes towards her uterus. It is about 1/100" in diameter, and is barely visible to the naked eye. It also considered by most of the public to be a form of human life, for the above reasons. But it does not meet some scientists' strict definition of a living organism, because it lacks one factor: the ability by itself to reproduce. It can only reproduce with the assistance of a spermatozoon. Some of these scientists have described an ovum as an "inert globule of organic matter." It does carry a cargo of human DNA.
At conception: One very lucky spermatozoon out of hundreds of millions ejaculated by the man will penetrate the outside layer of the ovum and fertilize it. This happens typically in the outer third of one of the woman's Fallopian tubes. The surface of the ovum changes its electrical characteristics and normally prevents additional sperm from entering. A genetically unique entity is formed shortly thereafter, called a zygote. This is commonly referred to as a "fertilized ovum." However that term is not really valid because the ovum ceases to exist after conception. Half of the zygote's 46 chromosomes come from the egg's 23 chromosomes and the other half from the spermatozoon's 23. It has a unique DNA structure, different from that of the ovum and the spermatozoon. The zygote is "...is biologically alive. It fulfills the four criteria needed to establish biological life:
metabolism,
growth,
reaction to stimuli, and
reproduction." 1
It can reproduce itself through twinning at any time up to about 14 days after conception; this is how identical twins are caused.
Conception is the point that most, or all, pro-life groups and conservative Christians define as the beginning of pregnancy. 8 Most of these groups define the start of a human person as occurring at conception. The medical definition of the start of pregnancy is about 10 days later, at implantation. The zygote divides into two cells, called blastomeres. They subdivide once every 12 to 20 hours as the zygote slowly passes down the fallopian tubes.
About 3 days after conception: The zygote now consists of 16 cells and is called a 16 cell morula (a.k.a. pre-embryo). It has normally reached the junction of the fallopian tube and the uterus.
5 days or so after conception: A cavity appears in the center of the morula. The grouping of cells are now called a blastocyst. It has an inner group of cells which will become the fetus and later the newborn; it has an outer shell of cells which will "become the membranes that nourish and protect the inner group of cells." 3 It has traveled down the fallopian tubes and has started to attach itself to the endometrium, the inside wall of the uterus (a.k.a. womb). The cells in the inside of the blastocyst, called the embryoblast, start forming the embryo. The outer cells, called the trophoblast, start to form the placenta. It continues to be referred to as a pre-embryo. 2
9 or 10 days after conception: The blastocyst has fully attached itself to endometrium. Primitive placental blood circulation has begun. This blastocyst has become one of the lucky ones. Most never make it this far in the process.
12 days or so after conception: The blastocyst has started to produce hormones which can be detected in the woman's urine. This is is the event that all (or almost) all pro-choice groups and almost all physicians (who are not conservative Christians) define to be the start of pregnancy. If instructions are followed exactly, a home-pregnancy test may reliably detect pregnancy at this point, or shortly thereafter.
This is the URL if your interested in reading the rest.
http://www.religioustolerance.org/abo_fetu.htm
Previously TipsyDipsy.
