Main Page Dynamic Development
The Foundations of Developmental Biology
From Sperm and Egg to Embryo
Genetic Regulation of Development
Organizing the Multicellular Embryo
Generating Cell Diversity
Dynamic Development at a Glance
Although the human embryo is not accessible to experimentation, a great deal of
information about human development has been obtained by investigators, and considerable
information about human development is available on-line. Why not? We are all curious
about the biology of our own species - particularly reproduction.
Movie 1: best.mpg.
- Although it is a bit fanciful, we shall start with an animated representation of Ovulation, which was produced
by The Biomedical Visualization Laboratory of The University of Illinois at Chicago (UIC).
This movie sequence shows an ovum being expelled forceably from a swelling on the surface
of the ovary and entering the fallopian tube via the infundibulum of the tube. Although
they are not represented very clearly here, the ovum is surrounded by non-cellular zona
pellucida and the corona radiata, which is a remnant of the granulosa cells that
surrounded it in the follicle. You can see the finger-like fimbriae that surround the
infundibulum and sweep over the surface of the ovary to collect ova as they are expelled.
The ovum passes into the ampulla of the tube, propelled by ciliary action of tubal
epithelial cells and muscular contraction of the tubal wall. Fertilization of the ovum
usually occurs in the ampulla as the ovum passes down the tube to meet the sperm, which
are propelled up the tube.
We shall next examine a three-part sequence on fertilization that was also produced at
Movie 2: meva1.mpg. (Part I)
- You will see sperm swarming in the vicinity of the ovum. The animator zooms in on the
surface of the corona just before one of the sperm passes through it. Notice the acrosome
on the head of the sperm.
Movie 3: meva2.mpg. (Part II)
- The fertilizing sperm passes through the corona, penetrates the zona and lands
tangentially on the surface of the ovum. The acrosome reaction occurs during this transit.
As the sequence ends, the plasma membrane of the sperm in the equatorial region fuses with
that of the ovum, and the sperm nucleus enters the egg cytoplasm and approaches the egg
pronucleus. The animator has not shown the completion of the second meiotic division and
the formation of the second polar body.
Movie 4: meva3.mpg. (Part III)
- The zygote initiates cleavage within the zona pellucida. Note, particularly, the
rotation of blastomeres that occurs after the second cleavage.
An on-line tutorial of the first four weeks of
human development, produced at The University of California, San Francisco, will be
our next stop. Begin with Week 1. We've advanced from animation to reality. First, examine
the image of the ovum, surrounded by the corona radiata. Then, continue with the rest of
the page and proceed to weeks 2-4. In week 2, there are three images that are not
labelled, these labels will be provided in the tutorial. Finally, there is a
self-testing exercise to evaluate your understanding of early human development.
Another site which you may find useful is: http://anatomy.med.unsw.edu.au/cbl/embryo/Notes/index.htm