here were people of all ages present at the picnic. There were even a few pregnant women (and maybe even a woman who didn’t know, yet, that she was pregnant) at the picnic. One woman, who was about 8 months pregnant, commented that her enlarged abdomen made a great place to balance her plate of food. . . until her baby kicked it off from within! The (human) children were really interested in one of the nanny goats who was also pregnant, and they asked if there were baby chicks in the eggs they were helping to collect.
Conception and Fetal Development
Since the eggs the children were collecting were just laid
by the hens and had not been incubated, those eggs would not have had
developing embryos within
them. In order for an embryo chick to grow and develop, a) the egg must be
fertilized by a rooster’s sperm, and b) the egg must be kept warm (incubated)
either by a hen or a man-made egg incubator. Then, 21 days later, a baby chick
will hatch from the egg. In order for an embryo human to grow and develop,
a) the mother’s egg must be fertilized by the father’s sperm, and b) about a
week later, the growing embryo must successfully implant in the mother’s
uterus, where it receives not only warmth, but also food and oxygen via the
placenta.
Every Spring in our Anatomy and Physiology course, Dr. Fankhauser and his
students study the development of chick embryos. A couple years ago,
Dr. Fankhauser photographed the steps in this process. He incubated eggs
for 48 and 72 hours (2 and 3 days) so the students could compare the development
of the two. This picture shows a circular hole which has been filed in the
eggshell and the shell being carefully chipped off, exposing the membrane
underneath.
Here, the membrane and remaining eggshell are being carefully removed. Since
the embryo floats on the top of the yolk, it is very important to keep the egg
hole-side-up, or the embryo will float out of
reach.
As shown in the photo at the very top of this page, the
embryo is carefully
lifted off the yolk with a life-preserver-shaped piece of filter paper, then
placed into a special salt solution and kept warm by shining a bright light
on it. In the photo, above, the white “stringy-looking” thing extending from
the center of the circle to about 9:00 is the embryo. The head is in the
center and facing upward, while the tail is to the
left.
Here is a photograph that Dr. Fankhauser took of a 48-hour chick embryo, along
with a labeled drawing I made of the same thing, back when I was in school.
Notice the heart “sticking out” to the right. The part labeled as “optic
cup” in the drawing is what will be the eye – that is somewhat visible in the
photograph. The part labeled as “otic vesicle” will become the ear. The
parts labeled “mesencephalon” through “telencephalon” are all parts of the brain.
One thing that’s not labeled in this drawing is the nerve cord which runs down
the center of the back (the “somites” are lined up on either side of the
nerve cord).
Here’s a photo he took of a 72-hour chick embryo, again, along with a labeled
drawing of the same thing. The heart, nerve cord, and eye are very visible
(The ear is quite visible, too, if you know where to look.).
It’s even possible to distinguish between the atrium and ventricle in the heart.
The part labeled as “olfactory pit” in the drawing will become the insides of
the nose. Notice the limb buds (“appendage buds”) beginning to form – these
will be the wings (“arms”) and legs. Also, notice the well-formed external
blood vessels. Just as a human baby has blood vessels (one artery and two veins)
in his/her umbilical cord to exchange nutrients, oxygen, and wastes with the
placenta, similarly a chick embryo has an “umbilical cord” of sorts, and the
blood vessels grow out to line the inside of the membrane, under the shell, so
they can absorb oxygen.
Here’s another of Dr. Fankhauser’s photos of a 72-hour chick embryo. Again,
the heart, eye, and nerve cord are quite recognizable, the ear is somewhat
visible, and the limb buds should also be pretty easy to find by comparing
with the labeled drawing.
OK, are you wondering, yet, what this has to do with
human biology?
Human embryos go through all the same stages, and at these early stages of
development, look practically identical to chick embryos! If a woman has
sexual intercourse midway through her menstrual cycle, around the time she
ovulates, it is likely that a sperm will fertilize her egg, forming a
zygote, the first, one-celled stage of the couple’s new baby. During
the third week of the woman’s cycle, that new embryonic baby is traveling
down her fallopian tube toward her uterus and simultaneously growing into
a multicellular (many-celled), hollow-balled blastocyst. By the
end of the third week of her cycle, the blastocyst has entered her uterus
and implants into the nutrient-rich uterine wall. By the time the woman’s
menstrual period is about 1½ weeks overdue, the baby is 3½ weeks (24-25 days)
old and looks very similar to the 48- or 72-hour chick embryos pictured
above. By the time the woman’s period is two weeks late and she’s beginning
to suspect she might be pregnant, the embryonic baby is four weeks old and
more advanced than the 72-hour chick embryo with limb buds (future arms and
legs) that are more developed and obvious. Just as the 48- and 72-hour chick
embryos’ hearts are already beating, so too, the heart of that four-week-old
baby has been beating for several days, already. By 10 weeks after fertilization,
all the baby’s organs and systems have formed (but still need to do a lot of
growing and developing), and (s)he is, then, called a “fetus” rather than an
embryo. From then on, it’s just a matter of growing and
maturing.
Some of the most outstanding work that has enabled us to
see what human
embryos and fetuses look like is that of Swedish photographer Lennart Nilsson
whose photos – many from ectopic (tubal) pregnancies – have been published in
magazines such as “Look” and “Life” as well as a number of books and
movies.
Links to Related Information on Our Web Server
The following Web pages contain information related to
prenatal development.
There will be one, combined assignment for the Reproductive System and Prenatal Development topics. Thus, even though this will appear on each of those pages to remind you, you only need to do it once. You are asked to pick either a contraceptive or an assisted reproduction technique or a sexually-transmitted disease (STD) or a genetic disorder that affects the reproductive system, and do further “research” to learn more about your chosen topic. The grading criteria for this assignment are given below, and you should also refer to those as you work on the assignment. A total of xx points is possible.
1. Background Information: | ||
---|---|---|
2 | — | The background information was very thorough and detailed |
1 | — | The background information was OK |
0 | — | The background information was skimpy or lacking |
2 | — | The background information was correct |
1 | — | The background information was mostly correct, but had a few mistakes |
0 | — | The background information was mostly incorrect |
2. Description: | ||
2 | — | The description for the chosen topic was very thorough and detailed |
1 | — | The description for the chosen topic was OK |
0 | — | The description for the chosen topic was skimpy or lacking |
2 | — | The description information was correct |
1 | — | The description information was mostly correct, but had a few mistakes |
0 | — | The description information was mostly incorrect |
3. Side Effects: | ||
2 | — | The side-effects information was very thorough and detailed |
2 | — | The side-effects information was OK |
0 | — | The side-effects information was skimpy or lacking |
2 | — | The side-effects information information was correct |
1 | — | The side-effects information information was mostly correct, but had a few mistakes |
0 | — | The side-effects information information was mostly incorrect |
4. Overall:: | ||
2 | — | The grammar, English usage, punctuation, and spelling were very good |
1 | — | The grammar, etc. were OK |
0 | — | The grammar, etc. were poor |
2 | — | The student, obviously, went beyond the minimum requirements of the assignment |
1 | — | The student adequately completed the assignment |
0 | — | The student completed considerably less of the assignment than what was required |
2 | — | It is evident that the student used much insight, thoughtfulness, and critical thinking when completing this assignment |
1 | — | The student adequately thought about the assignment – there was, perhaps, a bit of “fuzzy thinking” in a couple places |
0 | — | The assignment gives the appearance of being “slapped together” just to get it done, with little evidence of thoughtfulness |
Total Possible: | ||
18 | — | total points |