6 day old human embryo i slicno
6 day old human embryo implanting - coloured
6 day old human embryo beginning to implant into the lining of the uterus (endometrium). As implantation progresses, the inner cell mass begins to form into the bilaminar disc. The two layers are called the epiblast and the hypoblast. An embryo that has been in culture for up to 14 days will remain at this stage of development. Such cultured embryos remain alive but do not progress as they would in the womb.
Human egg with coronal cells - gold
Colour-enhanced scanning electron micrograph of a human egg. The egg is surrounded by a glycoprotein coat called the zona pellucida which aids in trapping and binding the sperm. Two residual coronal cells from the ovarian follicle are attached to the zona pellucida. The egg is sitting on the point of a pin.
Early human embryos
A collection of early human embryos of different stages, from the just fertilized egg to the blastocyst ready to implant in the uterine wall.
Sperm on the surface of a human egg
SEM Colour-enhanced scanning electron micrograph of human sperm attempting to fertilise an egg . The sperm burrow through the meshwork of the zona pellucida to reach the egg cell membrane (oolemma) where the successful sperm will become incorporated almost completely into the egg. Once the sperm has fused to the egg cell membrane the "zona reaction" takes place which prevents other sperm from entering the egg.
Human embryo exposing the embryonic cells
Scanning electron micrograph of a human embryo at day 4. The protein coat surrounding the egg (zona pellucida, gold) has been slit to expose the embryonic cells inside (red). These cells go on to form the embryo and can be harvested and cultured to give rise to embryonic stem (ES) cells. Microvilli are visible on the surface of the embryonic cells (blastomeres) and numerous sperm (blue) are still visible on the outside of the zona pellucida.
Human embryonic stem cell
Human embryonic stem cell (gold) growing on a layer of supporting cells (fibroblasts). Stem cells are derived from very early embryos and can either be grown to stay in their original state or triggered to form almost any type of human cell. The fibroblasts provide special factors that maintain the stem cells in their original state. The stem cell appears to be grasped by the underlying fibroblast. Stem cell research could lead to cures for many diseases such as Parkinson's disease, Alzheimer's and diabetes, where a patient's cells are damaged or absent.
Newly fertilised human egg
Human egg soon after fertilisation viewed using Nomarski optics. The two parental pronuclei are clearly visible and have not yet fused.
Human embryo after zona drilling - coloured
Colour-enhanced scanning electron micrograph of a human embryo at day 3. The egg has been fertilised in vitro and has developed to this stage in culture. The coat around the egg (zona pellucida) has been treated with acid Tyrodes solution to make a hole so an individual cell can be removed. This cell can then be used for genetic diagnosis before the embryo is transferred to the woman's uterus. This allows the selective implantation of embryos that do not carry the genetic disease in question.
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