Conception

Conception, or fertilization, is the union of an ovum, or egg cell, and a sperm. Conception usually occurs in the Fallopian tube when a sperm penetrates an ovum and forms a zygote. A zygote is a single cell that contains genetic material from each parent.

As the zygote moves through the Fallopian tube, cell division continues to occur. This results in a cluster of cells that reach the uterus. These cells begin to attach themselves to the endometrium, the lining of the uterus. By the end of the first week of development, these cells have become fully attached or implanted. This marks the beginning of an embryo. An embryo is developing cluster of cells.

The outer cells of the embryo and cells of the endometrium form the placenta. The placenta is an organ that anchors the embryo to the uterus. Other cells form the umbilical cord. The umbilical cord is the structure that connects the embryo to the placenta. Blood from the mother carries nutrients and oxygen to the embryo through the cord. Waste products from the embryo move to the mother to be excreted from her body. Occasionally, the zygote does not move to the uterus. An ectopic pregnancy results. An ectopic pregnancy is the growth of a fertilized egg in a part of the body other than the uterus. The most common site of an ectopic pregnancy is in the Fallopian tube. One cause of an ectopic pregnancy can be a blocked Fallopian tube. Infection is the most common cause of such blockage.

A n ectopic pregnancy can end in one of two ways. The embryo may enter the abdominal cavity and disintegrate. Or, the embryo may expand and stretch the tube causing it to tear or rupture. This would cause pain, bleeding, and infection. If this occurs, a woman's life can be in danger. Medical attention is needed immediately.

Occasionally, a zygote splits in half and each half forms an embryo. Identical twins are two babies that develop from the same egg and sperm. Identical twins have identical chromosomes so they are always the same sex and always look exactly alike.

One egg cell may be released from each ovary at the same time. If each egg is fertilized by a different sperm, fraternal twins will develop. Fraternal twins have different combinations of chromosomes because they developed from separate eggs and sperm. Fraternal twins are not necessarily the same sex and may not look alike.

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сonception/fertilization to penetrate cell division the lining of the uterus to anchor umbilical cord ectopic pregnancy to disintegrate to stretch the tube identical twins fraternal twins

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