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Normal Pregnancy |
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The Female Reproductive Systems
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The female reproductive system includes the vagina, cervix, uterus, Fallopian tubes,
and ovaries. The female contribution to reproduction is the egg or ovum. An ovum
is larger in size than the sperm cell and always carries an X chromosome. In every
ovulating woman of reproductive years every month (until menopause) a mature ovum
is released from a follicle located in one of the ovaries. The ovum then moves into
the Fallopian tube. If it is fertilized by a sperm within the Fallopian tube, pregnancy
may occur.
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Female Genital Tract
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The Male Reproductive System
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The male reproductive system includes the testes, epididymis, vas deferens, ejaculatory
ducts, seminal vesicles, prostate, bulbourethal glands, urethra, and penis. In order
for reproduction to occur, the male must contribute healthy and living sperm. Each
individual sperm cell is composed of a head, mid-piece, and tail. Sperm move by
whipping their tail around in an elliptical cone. Furthermore, a sperm cell will
either carry an X or Y chromosome. The Y chromosome will result in the production
of an embryo with a male genome upon fertilization, whereas an X chromosome will
result in the production of a female genome upon fertilization. Thus, it is the
male that contributes to the sex of the zygote. During ejaculation, the sperm move
through the vas deferens and into the ejaculatory ducts, where they are mixed with
fluids from the prostate, seminal vesicles, and bulbourethal glands to form semen.
The semen will then pass through the urethra and out of the penis.
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Male Genital Tract
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Events that take Place During Normal Pregnancy
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During sexual intercourse and after ejaculation, the sperm must travel through the
cervix and uterus, and into the Fallopian tubes. If sexual intercourse occurs at
the time of ovulation, the sperm will meet an ovum in the Fallopian tube and fertilize
it forming a single fertilized cell or “Zygote” or embryo.
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Summary of Ovulation, Fertilization,
and Implantation of the Embryo in the Uterus
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The zygote will then begin to divide or undergo cleavage as it moves through the
Fallopian tube to the uterus, transforming sequentially from a single cell to the
2-cell stage after 24 hours, the 4-cell stage after 36-48 hours, and the 8-cell
stage 72 hours after fertilization. The cells of the embryo continue their division
forming a mulberry ball of cells or “Morula” after 4 days. After 5-6 days the ball
of cells develops a fluid filled area in its center forming a "Blastocyst."
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Zygote |
2-cell |
4-cell |
8-cell |
Morula |
Blastocyst |
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In order for embryonic development to continue, implantation needs to take place.
The blastocyst must hatch from the zona pellucida, a protein matrix that surrounds
the embryo, and attach to the endometrial lining of the uterus. If implantation
occurs, then the mother will begin the gestation period.
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Blastocyst Hatching |
Blastocyst Implanting |
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The gestation period for humans is nine months (about 40 weeks), and this time interval
is usually divided into three trimesters (each 3 months long). Successful completion
of the nine month gestation period will result in childbirth.
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Increase in Weight and Size by the Baby
and Mother (Weeks 6, 12, 20, and 36)
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Increase in Size of the Uterus |
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