There were people of all ages present at the picnic. Placing Embryo on Slide 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.

Removing Shell 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.

Removing Membrane 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.

48-hr Photo 48-hr Drawing
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).

72-hr Photo #2 72-hr Drawing
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.

72-hr Photo #1 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.


Background Information

Links to Related Information on Our Web Server

The following Web pages contain information related to prenatal development.

Bio Lecture Sex-Linked Genes
Pay special attention to the section on the effects of AIS on prenatal development
Bio Lecture Conception, Prenatal Development, and Birth
Pay special attention to the sections on embryonic and fetal development and the birth process

Your Assignment
Reproductive System

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. If you choose a contraceptive,
  2. If you choose an assisted reproduction technique,
  3. If you choose a sexually-transmitted disease,
  4. If you choose a genetic disorder that affects the reproductive system,
  5. At this point, if you are a registered student, you should submit your work.

Grading Criteria

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

Copyright © 2006 by J. Stein Carter. All rights reserved.
This page has been accessed Counter times since 18 Nov 2006.