General Understanding of Human Reproduction and Conception

For many years before a baby is conceived, the bodies of his parents have been getting ready for his conception. The mother’s body has been producing egg cells (ova), and the father’s sperm cells (spermatozoa) to fertilize them. Once an egg is fertilized, the baby needs a place to grow and develop; the mother’s body has prepared such a place.

When a girl reaches her teens her body begins to change, making it possible for her to produce and carry a baby. Her hips widen so that the pelvic cavity is large enough to hold a baby and allow it to pass through the birth canal. Her breasts enlarge so that after the baby is born, she can supply milk for him.

Many changes are also going on inside her body. Each month one egg cell (ovum) is maturing and being released from one of her two ovaries. The ovaries are the storage place for undeveloped egg cells. An egg cell looks something like a hen’s egg, except that it is the size of a pinpoint. It has a yellow center with a fluid around it. The outer covering or membrane is tough, but not as hard as a hen’s eggshell.

Each month the uterus, of the womb, where the baby will grow, develops a special lining of blood vessels, which can nourish a baby. If an egg is not fertilized, it continues on its path through the birth canal to the outside. Then the special lining in the uterus pulls away from the uterus wall and also passes on to the outside since it is not needed to nourish a baby. The process by which this lining is discarded is called menstruation. A girl’s body will prepare an egg cell and a fresh lining in the uterus approximately every month from the time she is 12 or so until she is in her 40s or 50s.

A boy also begins preparing for fatherhood early in his teens. (Child Birth,732) At the time sperm cells, will start maturing. Sperm cells are much, much smaller than egg cells. They look somewhat like a tadpole with a round head and long tail. This tail makes it possible for the sperm cells to move.

Millions of sperm cells mature constantly in males, rather than just one cell per month as egg cells do in females. The male body can produce sperm cells until age 80 or 90.

A boy also produces a slippery fluid called semen, which mixes with the sperm cells. Occasionally he will have such a build up of semen that his body will automatically release it.

This is called nocturnal or seminal emission. It is also referred to as a “wet dream” since it happens often during sleep.

As an egg cell matures or ripens, it’s released by the ovary. It is quickly drawn into a tube called the fallopian tube or oviduct, which connects the ovary with the uterus. The tube is about three to five inches long and is lined with tiny hair-like projections which move back and forth. These hair-like projections brush the egg cell along on its journey. It takes the egg three to four days to reach the uterus, whether it is fertilized or not. (Child Birth,733).

If there are live sperm cells in the fallopian tube, they will bump into the egg cell and surround it. Sperm cells make an enzyme or chemical, which will dissolve the tough membrane around the cell.

After great many sperm cells have bumped into the egg cell and deposited this enzyme, some of the membranes will be dissolved. Then the next sperm cells to bump into the egg cell will go right through into the egg.

Many sperm cells may enter the egg cell, but only one sperm head or nucleus can unite with the egg cell’s nucleus.

The first sperm cell to reach the nucleus of the egg will live. All the rest will die in a few hours.

One major difference between sex cells and all other human tissue cells is that sex cells do not have the normal number of chromosomes or heredity-determining factors. All other cells have 46 chromosomes. Egg cells and sperm cells are half complete, having only 23 chromosomes. When the two nuclei of the sex cells meet and unite, they form a complete cell with 46 chromosomes.

This cell is the start of a new human being.

For a few hours after meeting, the two nuclei, one from the sperm cell and one from an egg cell, lie next to each other in the center of the egg cell.

The tail drops off from the sperm cell so that the two nuclei look alike. After this brief rest, a rush of activity begins. The two nuclei move together and the chromosomes pair up to make 46 needed to be a complete human tissue cell. But it’s no ordinary cell. Almost immediately this new cell splits into two identical cells. They are smaller and still fit in the same membrane; like the original cell, each has 46 chromosomes.

Cells divide by a process called mitosis. All cells plant, animal, and human go through approximately this same procedure to reproduce. The chromosomes make copies of themselves and then gather in the center of the cell. In human tissue cells, this would.

mean that 92 chromosomes are crowded into the egg seems to disappear, and the double chromosomes start to pull apart. The dividing cell looks like a football with magnets at each end. Each “pole” or end seems to be attracting half of each chromosome pair. Forty- six chromosomes are drawn to one end and 46 are drawn to the other end.

As they gather at each end, a nucleus membrane grows around each cluster. This separates them permanently, and they become two complete, identical cells.

After a brief rest, these two cells will also undergo mitosis and split into four identical cells. The four will rest and then divide into eight, and so on, Each time only smaller. In three days there are about 32 cells. (Child Birth,788) In four days about 90 identical cells are crowded into the original egg cell’s outer membrane. This rather bulgy collection of cells is still traveling along the fallopian tube on its way to the uterus.

During this time the only nourishment the cells receive comes from small particles of fat and other substances present in the original egg cell.