sp_story.htm

The images shown here are excerpted from a book, "Behold Man". Its author, Lennart Nilsson, photographed and documented these biological events of immense significance almost single handedly. This book may now be out of print, but is available at the Upstate Medical University (Call Number Qs 17N 712s 1974)

The ovum surrounded by a protective membrane, travelling through the Fallopian Tube. (For more information, see "Behold Man", Little & Brow, p.46, 1974)

Three weeks old embryo. At this stage the mother may not know that she is pregnant. (For more information, see "Behold Man", Little & Brow, p.52, 1974)

Four weeks old embryo, 1/5" long. Note the characteristic bending of the embryo. (For more information, see "Behold Man", Little & Brow, p.52, 1974)

Five weeks old and 2/5" long, the embryo floats in amniotic fluid anchored to the placenta by the umbilical cord. (For more information, see "Behold Man", Little & Brown, p.52, 1974)

Six weeks old and 3/5" long, the embryo rests securely in the shock absorbing amniotic sac. (For more information, see "Behold Man", Little & Brown, p.53, 1974)

Seven weeks old and nearly 1" long, a tiny human being with all its outer and inner organs formed is now developing rapidly. (For more information, see "Behold Man", Little & Brown, p.53, 1974)

Eight weeks old, slightly over 1" long and 2.5 g, the baby is now growing by a few mm/day. The two umbilical veins carry oxygenated blood from the placenta to the embryo -- now called the fetus.(For more information, see "Behold Man", Little & Brown, p.54, 1974)

Four months old, over 6" long, and about 7 oz, here is an active fellow who puts his feet against the amniotic sac and has hands ready to grasp. All the organs have been formed. (For more information, see "Behold Man", Little & Brown, p.54, 1974)

The interplay of many factors acting together in concert with the ovulation process help sperm and egg to find each other. As a First step, the glands surrounding the cervix, stimulated by a surge in the production of an ovarian hormone during midcycle, secrete a gel like mucus. This cervical mucus is a structural network of loose bundles of fibres made of glycoproteins.

Sperm penetrates the cervical mucus within a few minutes of intercourse, and the gel is sucked into the uterus by peristalsis. The viscus flow created by the peristaltic movement, orients sperm as they progress toward the upper part of the uterus. Under the influence of the fluid movement, sperm are forced to swim in a streamline parallel to the direction of the flow. Sperm morphology and its specific tail movements may play an important role at this stage of transport (Click for demonstration). There are tufts of hair like structures called cilia on the surface layer of the oviduct. The tips of these cilia rake the mucus, and with each synchronous ciliary beat, the viscous mass pulls forward clusters of sperm still embedded into the gel. Sperm by themselves swim rather slowly, an equivalent of one of its body length in 2 seconds, compared to the total distance they must travel. So for a long distance lap, Sperm need a variety of help to make a successful journey from the cervix to the deep end of the fallopian tube.

The egg cell is relatively large, so large that with proper lighting it can be seen with naked eyes, as seen in the picture on the right, as a speck at the opening of the fallopian tube. At ovulation, the fringe at the end of the fallopian tube is activated, and its function is to guide the egg into the tube. The fallopian tube has all the provisions needed to create the optimum ambience for fertilization. In addition to the uterine and tubal activities to facilitate sperm transport and uniting sperm with the egg, there may also be oriented sperm movement guided by a concentration gradient of steroids released with the follicular fluid streaming into the tube with the newly released egg.

Successful fertilization needs the entry of a single sperm into the egg cytoplasm. Although many sperm attach to the egg only one succeeds in penetrating the zona and it must immediately inhibit the penetration by others. The green cap on the sperm head shown in the photograph is called the acrosome, that is essential for the attachment and penetration processes.

The sperm that succeeds in penetrating, must bring with it a headfull of intact and a complete quota of haploid amount of human DNA. The headfull of DNA stained blue as shown in the photograph, was revealed by removing the green stained acrosome structure.

The ovum outside the Fallopian Tube. The egg cell, only a fraction of a millimeter in size, is the light blue spot at the left of the Fallopian Tube. (For more information, see "Behold Man", Little & Brown, p.45, 1974)