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Human Reproduction

Overview

The reproductive process actually consists of multiple processes that must successfully occur at exactly the right moment. Any interruption in this complex sequence of events can prevent fertilisation and /or implantation.

01. Human Reproduction
02. Female Reproductive System
03. Male Reproductive System

Human Reproduction

The reproductive process actually consists of multiple processes that must successfully occur at exactly the right moment. Any interruption in this complex sequence of events can prevent fertilisation and /or implantation.

  • Fertilization
  • The role of the woman
  • The role of the man
  • The role of the embryo

Fertilization:
What exactly is necessary to conceive naturally?

Many successive steps are required:

  • The release of a fertile ovum (egg).
  • The production of healthy sperm.
  • The sperm must be able to reach the ovum (requiring healthy cervical mucus and viable fallopian tubes).
  • The sperm cells must be able to fertilise the ovum.
  • The fertilised embryo must be able to implant itself in the lining of the womb.
  • But these steps are just the key processes involved in becoming pregnant. There are many other factors that play a pivotal role in determining whether a pregnancy will result in the birth of a (hopefully healthy) baby. The more you learn about the reproductive organs and the complex fertilisation process, the more incredible it seems that the process succeeds so often without medical help. The description below provides a very simplified outline of what is involved in becoming pregnant and is only intended to provide an initial insight into the process. You must not forget that, with every step, many complex underlying processes are involved.

    The role of the woman:
    In general, a woman releases one egg or ovum a month from one of her two ovaries. This ovum is expelled from the ovary into the fallopian tube. The ovum passes along the fallopian tube in anticipation of meeting the male sperm. At the same time, the womb begins to prepare for the possible implantation of a fertilized ovum.

    The role of the man:
    The male sperm obviously plays just as critical a role in the reproductive process. After ejaculation into the vagina, the male sperm swims through the cervix of the female, and then through the womb and into one of the fallopian tubes. Fertilisation occurs when a sperm cell encounters the ovum (egg) in the fallopian tube and penetrates it (fertilisation).

    The role of the embryo:
    As soon as the ovum is successfully fertilised, it is referred to as an embryo. This embryo moves further down the fallopian tube into the womb. In order to develop further, this embryo must attach itself to the wall of the womb, a process referred to as implantation. The factors that influence the complex implantation process are still not completely understood.

    Female Reproductive System

    An examination of the reproductive process clearly shows that there are numerous points where the process might not succeed resulting in failure to achieve pregnancy.

    The female reproductive system consists of 3 main parts:

    • Ovaries
    • Fallopian tubes
    • Womb (uterus)

    Ovaries:
    The ovaries are small, oval-shaped organs, which are located just below the fallopian tubes on either side of the womb (uterus). The ovaries contain fluid-filled bubbles or follicles that in turn contain immature, or unripe, egg cells (ova). All these egg cells were produced by the woman when she was a foetus. Yet only a fraction of them will actually develop into mature, or ripe, ova during her life. After puberty, many ova will start the development process each month, although usually only one will be released or ovulated each month. After ovulation, the ovum enters the fallopian tubes.

    Fallopian tubes:
    The fallopian tube is the site of fertilisation. While the fallopian tube appears to be a simple organ, it is actually quite complex. Each tube has fan-shaped ends or fingers, the so-called fimbriae, which brush along the ovary and collect the ovulated egg (ovum). The fallopian tube, which has a circumference of almost 1ľ centimetre at the open end near the ovary, narrows when it approaches the womb to the diameter of a pencil tip. The end closest to the ovary constricts in order to push the ovum down to the site of fertilisation, while the end that is closest to the womb pulls itself up in order to aid the passage of sperm along the tube. Throughout the process of fertilisation, the fallopian tube creates the right environment to maintain the female ovum and the male sperm. It can take some days for the ovum and subsequently the embryo (fertilized egg) to negotiate the length of the fallopian tube and reach the womb.

    The fallopian tubes have the following tasks:

    • Picking up the released ovum (egg).
    • Providing sustenance and movement for the ovum.
    • Transporting sperm to the ovum.
    • Creating the śright environment for fertilisation
    • Transferring the embryo (fertilised ovum) to the womb.

       Womb (uterus):
      The womb is a hollow, pear-shaped organ, situated low in the female pelvis. It is often referred to as the uterus. After ovulation (egg release), the lining of the womb grows in anticipation of receiving an embryo (fertilized egg) from the fallopian tube. Following successful implantation, it protects, develops and feeds the foetus until birth. If a woman is not pregnant, then the lining of the womb - known as the endometrium - is shed when she begins her menstruation (period).

    Cervix (Cervix Uteri):
    The cervix is the connection between the lower part of the womb and the vagina. It produces mucous like secretions that change during the reproductive cycle both in terms of the amount produced and its composition. During the womans fertile days around the time of ovulation, the cervical mucous is thin and watery in order to aid the passage of sperm into the womb. After ovulation and/or during pregnancy, the cervical mucous thickens to form a protective barrier against foreign substances and infections. An increase in healthy vaginal secretion halfway through the cycle can be an indication of the approaching ovulation.

     

    Female Reproductive Physiology:
    The monthly cycle of a woman is a complex process involving a great many organs and hormones. To begin with, on the first day of menstruation (day 1 of a womans cycle), the body starts to produce and release ever-increasing amounts of follicle stimulating hormone (FSH). This hormone, produced by the pituitary gland at the base of the brain, ensures that the follicles grow and produce oestrogen, the female hormone. At that point, the eggs developing inside some of the follicles begin to ripen, or mature. During the average cycle, on day 14, the pituitary gland releases a large amount of yet another hormone, called luteinizing hormone (LH); this is called the LH-peak. LH stimulates the ultimate maturation of one egg and starts the ovulation process - the release of a mature egg by the dominant follicle and the ovary. During the time that the released egg moves through the fallopian tube, the ovulated follicle produces levels of another hormone, called progesterone. Progesterone instructs the lining of the womb to prepare for the implantation of a fertilised egg (embryo). The first half of the cycle (in which the follicles mature) is called the follicular phase; the second half is referred to as the luteal phase. If sperm cells are present in the fallopian tube, the egg (ovum) can be fertilized and the resulting embryo moves down the fallopian tube to the womb, where it can implant and hopefully grow into a baby. In the event that the ovum is not fertilized, it still moves towards the womb, but is unable to implant and simply degenerates. Approximately two weeks after ovulation, the non-pregnant womb sends a signal to the ovary to decrease progesterone production. As a result, the lining of the womb is shed and released through menstruation. The whole cycle then begins once again.

    Male Reproductive System

    The male reproductive system consists of 3 main parts:

    • Testicles
    • Epididymis
    • Vas deferens (sperm ducts)

    Testicles (testes):
    The two testicles, normally about four to five centimetres long, are found in the scrotum (a structure made up of multiple layers of muscles which protect the testicles and help control their temperature). The testicles have two very important functions, both of which are essential for normal male fertility: the first is the production of the male hormone testosterone; and, the second is the production of sperm cells (spermatozoa). The development of sperm starts in the testicles. From here, they travel to the epididymis.

    Epididymis:
    The epididymis is a long, narrow spiral-shaped tube surrounded by a layer of connective tissue. Rolled out, the epididymis would be approximately six meters long! The epididymis is found at the back of the testicles and is divided into a head, body and tail. Here the sperm undergoes its final development and maturation, and is stored until ejaculation. From the epididymis, the sperm travels to the vas deferens (sperm ducts).

    Vas Deferens:
    The vas deferens or sperm ducts have a long, tube-shaped structure that connects the epididymis (where the sperm is stored) with the urinary tract (through which the sperm is discharged). While the urinary tract - as the name suggests - also releases urine, the presence of a valve prevents the simultaneous discharge of sperm and urine. During ejaculation, the sperm streams from the testicles through the vas deferens into the urinary tract. As the sperm leaves the body via the penis, the prostrate and other glands add seminal fluids. When a male is sterilised, both vas deferens are severed so that sperm can no longer enter the urinary tract and are not present in the ejaculate.

    Sperm Cells (Spermatozoa):
    The ejaculate mostly contains fluid originating from the prostrate and the sperm fluid creators, as well as millions of sperm cells. Both the quantity and the quality of the sperm cells are critical when it comes to fertilisation. In the laboratory, the ejaculate can be examined for numerous characteristics including:

    • The volume of ejaculate (in millilitres, 2 - 5 ml)
    • Concentration of sperm cells (number/ml)
    • Mobility of sperm cells
    • Number of living sperm cells
    • Appearance of sperm cells
    • Agglutination or clotting together of sperm cells

    The World Health Organisation (WHO) has created criteria for a śnormal result (normospermic).

    Normal Male Reproductive Physiology:
    The production of sperm - a process termed spermatogenesis - is a highly complicated process that begins during puberty and continues, in healthy men, until death. The process starts in the testicles and is regulated by various hormones. These hormones are in turn regulated by the hypothalamus and the pituitary gland in the brain. The hypothalamus controls the hormonal activity of the pituitary through secretion of gonadotropin-releasing hormone (GnRH). This hormone in turn controls the production of the gonadotropins, follicle stimulating hormone (FSH) and luteinizing hormone (LH) by the pituitary. LH activates the production of testosterone (a hormone essential for sperm production), while FSH also activates other hormones that assist in the production of sperm. Besides sperm production, testosterone is also responsible for virility, male hair growth and muscle growth. From start to finish, the production of sperm takes approximately 72 days. For the first 50 days, the sperm remains within the testicles moving into the epididymis for the remainder of this time. In the epididymis, the sperm mature and gain their mobility (the ability to swim). During sexual intercourse, the sperm is ejaculated into the female reproductive tract via the vagina and commences its journey (of approximately 12cm) through the cervix and the womb to the Fallopian tubes, the site of fertilisation. On the way, there are many cavities, folds or wrong turnings that prevent many sperm cells from reaching their final destination. This explains why so many sperm cells - millions - are needed to achieve fertilisation.

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    Dates 2015

    4 - 6
    Dec

    Annual Meeting of the Middle East Fertility Society

    Location: Liege, Belgium
    More information