physilogy of reproduction.docx

7/28/2019 physilogy of reproduction.docx

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FRANCAIS| ENGLISH |DE

hysiology of human reproductionhe female genital systems comprised of 2 ovaries (a), 2 Fallopian tubes (b), the uterus (c) and the vagina (d).

he female genital system.

varian reserve

he ovaries contain, very early during the development of the human fetus, all the ovules (or oocytes or eggs) necessary for thentire duration of the woman's reproductive life. The number of oocytes (reserve of follicles) is established as of the 5th month o

estation. Henceforth, it will only decline, rapidly until birth, then more slowly, becoming quasi-null at menopause.

he menstrual cycle
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he menstrual cycle

the onset of puberty, the menstrual cycles begin. This cycle generally lasts 28 to 30 days, with day 1 being the first day ofenstrual bleeding. A succession of modifications, orchestrated by cyclically produced specialized molecules - the sex hormonll change the ovaries and uterus. These hormones assure the communication among all the organs of the genital tract and the

ypophysis, a gland located at the base of the brain.

he 3 successive phases of the menstrual cycle are described below. The fol l icular phas e (or the phase of fol l icu lar maturation)very month, among the high number of oocytes on stock in the ovary, about 50 will become sensitive to secreted hormones.enerally, all but one of these will degenerate (undergo atresia). The oocyte that reaches maturity is contained in a small sac (t

licle), bathed in a liquid (the follicular fluid). This sac gradually expands, pushing against the outer wall of the ovary, in responlicle-stimulating hormone (FSH), which is produced by the hypophysis. The sac will reach about 2 cm in diameter just before

vulation, when the rupture of the ovarian wall releases the egg. The oocyte is a large cell that measures about 1/10th of allimeter in diameter. Unlike all the other cells in woman's body, the oocyte has only half the chromosomes (that is 23) that conthe genetic information that the woman will transmit to her descendents. The genetic or chromosomal content of the embryo

nly be constituted after the addition of the 23 chromosomes harbored in the fertilizing spermatozoid. During the follicular phasevaries also secrete hormones: estrogens. These hormones prepare the uterus to receive the embryo, should one be conceived

2 The ovulation ph ase


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vulation occurs around 14 days before the onset of menstrual bleeding, which means that a woman with a 28-day cycle willvulate around the 14th day of her cycle. However, if she has a longer cycle, ovulation will occur later. Ovulation is provoked bynother signal sent by the hypophysis, the luteinizing hormone (LH) peak. During ovulation, the oocyte is extruded from the follihose wall breaks, and is aspirated into the Fallopian tube. The oocyte now starts its migration towards the uterus.

The luteal phase (or preparation of th e uterus for the potential imp lantation of an embry o)

uring this phase, the wall of the uterus (called the endometrium) is prepared for implantation of the embryo resulting from thertilization of the oocyte by a spermatozoon. This process is dependent upon hormones released by the ruptured follicle from we oocyte was expulsed: the follicle is transformed into a corpus luteum (which means yellow body) and starts to secrete a newormone, progesterone.

he male genital system

he male genital systemconsists of the penis (1), the testicles (2), the epididymis (3), the deferent canals (4), the seminal vesicles (5) and the prostatehese tissues interact among themselves and with the hypophysis, in a manner similar to that seen in women.emen (the ejaculate) is constituted of seminal fluid secreted by several glands - the prostate and seminal vesicles - andermatozoa, mobile cells produced in the testicles. Normally, 1 milliliter of semen contains 20 to 100 million spermatozoa, amo

hich at least 40% are mobile.or spermatozoa to be present in sperm requires not only that spermatozoids be produced in the testicles, but also that these cn traverse the successive excretory pathways - epididymis, deferent canals and ureter.

permatozoa contain the genetic information that the man will transmit to his descendents. Just like oocytes, they contain only e number of chromosomes (23) as other cells in the body that contain 46 chromosomes. In addition, each spermatozoon conte chromosome that alone will determine the sex of the child: either the X chromosome for girls or the Y chromosome for boys


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agram of a spermatozoonspermatozoon is comprised of 2 parts: the head (1) and the tail or flagellum (2). This elongated cell is much smaller than an

ocyte (0.05 mm long). The head is covered with a hood called the acrosome (3), which contains active molecules (enzymes),hose role is to pierce a tunnel through the layers surrounding the oocyte so that the spermatozoon can deliver its chromosomntribution and thereby fertilize the egg. The flagellum's whip-like lashes assure the mobility of the spermatozoon in its progreswards the oocyte.

he stages of natural fertilization

he stages of natural fertilization


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uring sexual intercourse, spermatozoa are deposited at the far end of the vagina (1). They rapidly reach the cervical mucus (2edium in which spermatozoa can live for up to 3 days. The spermatozoa start their journey into and across the uterus (3), and nter the Fallopian tubes (4). One-third of the way into the Fallopian tube, the spermatozoa meet the ovule (5) that had beenxpulsed from the ovary (6).

ages of embryo development and implantationa spermatozoon and the oocyte meet (1), fertilization can occur. Only one spermatozoon can penetrate the zona pelucida, theotective wall surrounding the egg (2), and reach the oocyte membrane. The fertilized egg, now called a zygote, evolves rapidhile continuing on its way down the Fallopian tube to the uterus (4), (5) and (6). Sixteen to 18 hours after the encounter of theermatozoon and the egg, the 2 nuclei (the organelles within each cell that contain the genetic heritage or chromosomes) are

early visible, side-by-side, in the single cell. The fusion of these nuclei (3) leads to the formation of a new nucleus containing ae embryo's genetic information (46 chromosomes).

hirty hours after fertilization, the zygote starts its cellular divisions. These are repeated every 12 to 16 hours. This fertilized eggvides into smaller-and-smaller daughter cells, called blastomeres, until the morula stage (a spherical mass of blastomeres) isached. Thus, the volume remains constant within the zona pellucida surrounding the ovule.

nce the stage of about a dozen blastomeres has been reached, these cells undergo a phenomenon of compaction. This termefines the passage from morphologically round cells to those resembling flat building blocks (squamous epithelium), whichcreases the areas of contact among them. owards the 5th day post-fertilization, another decisive transformation occurs. The cells comprising the morula begin to move ine ball of cells (invaginate) and form an internal cavity, called a blastocele, in which fluid accumulates. The embryo has reache

astocyst stage: it is formed by a monolayer of cells around an internal cavity, which is the starting point for the development otal appendages, including the placenta, and by a mass of cells which will give rise to the fetus.


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lastocyst on day 5. Expanded blastocyst.om day 5, the blastocele will continue to dilate progressively until the zona pellucida becomes thin and ruptures (hatchedastocyst). At this stage, the embryo is made up of about 100 cells. he blastocyst (7) arrives in the uterus, where a favorable environment has been created under the action of the hormones releom the corpus luteum; it will penetrate into the uterine mucosa (endometrium), called implantation, where it will develop duringmonths of gestation.hus, multiple conditions must be met for pregnancy to occur: the female and male genital organs must function at optimal leveat ovulation and fertilization can proceed normally and an embryo can implant successfully in the uterus. uring the course of a natural cycle, a normally fertile couple has about a 25% chance of initiating a pregnancy. However, a widriety of events can intervene and prevent conception, in which case, we can talk about infertility or low fertility.

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physilogy of reproduction.docx