CONTENTS
Main Page Dynamic Development
The Foundations of Developmental
Biology
Gametogenesis
From Sperm and Egg to Embryo
Genetic Regulation of Development
Organizing the Multicellular
Embryo
Generating Cell Diversity
Dynamic Development at a
Glance |
Human Development
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 UIC.
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. |
