Erection of the penis and ejaculation of semen are necessary for the
placement of sperm in the female reproductive tract. Semen, also called
seminal fluid, is a mixture of sperm and secretions from the seminal vesicle,
the prostate gland, and the bulbourethral glands.
Section III. EVENTS OF PREGNANCY
Pregnancy is defined as the period of time between conception and the birth of
the child. The term pregnancy can be broken down into a series of events which
include the following: fertilization, implantation, gestation, and parturition.
Understanding each of these events can increase your effectiveness in aiding in the
delivery of an infant.
The union of ovum and sperm is called fertilization. Normally, fertilization takes
place in the outer one-third of the fallopian tube shortly after ovulation (the discharge of
ovum from the mature follicle) and insemination (introduction of the male's seminal fluid
into the female's vagina).
a. Zygote. To penetrate the ovum, the sperm releases the enzyme
hyaluronidase that makes the surface of the ovum more permeable. The sperm enters
the ovum. The nuclei of the sperm and the ovum fuse, making the process of
fertilization complete. A new cell, called the zygote, has been made. The zygote cell
has 46 chromosomes and all the potentials of the new individual such as sex, size, hair
color, and eye color.
b. Cell Divisions. The zygote begins mitotic cell divisions within the space of
hours after the zygote has formed. As a result of these divisions, this new zygote cell is
soon a fluid-filled ball of cells.
While these cell divisions are taking place, the zygote is traveling along the
fallopian tube. The zygote reaches the uterus in about three to four days, implanting
itself in the uterine lining. This implantation, the embedding of the fertilized ovum in the
lining of the uterus, has taken place about seven days after the ovum was fertilized.