Fertility
Definition
What is Fertility?
Getting pregnant involves a number of complex stages. Each of these stages
must be successfully completed before a positive pregnancy test can be
achieved.
In a normal menstrual cycle, a woman usually produces a single egg grown
in a fluid filled sac known as a follicle. This process starts at the
beginning of each menstrual cycle, day 1 being the first day. Between
day 2 and day 6, a hormone known as Follicle Stimulating Hormone (FSH)
is produced. This triggers a number of follicles to develop in the ovary.
Only one of these follicles will produce a mature egg which will become
a dominant follicle, the others will stop growing.
As the dominant follicle continues to grow, it starts to release another
hormone, Oestrogen. Oestrogen also helps the lining of the uterus, known
as the endometrium, to thicken.
When the Oestrogen has reached a certain level, the FSH levels reduce.
Another hormone known as Luteinizing Hormone (LH) is produced. LH matures
the egg in the follicle and the now mature egg is released from the follicle
24-36 hours after the highest LH peak.
Dominant Follicle
The egg then passes into the fallopian tube. The follicle that has ruptured,
releasing the egg, is now referred to as the Corpus Luteum (CL). The Corpus
Luteum continues to produce Oestrogen, but in addition also produces another
hormone known as Progesterone. Progesterone enables the endometrium to
further thicken. This is important to form a receptive environment for
the later embryo to implant.
The released egg is viable for fertilisation to occur within the fallopian
tube for a limited period of time, approximately 12-24 hours. This is
around day 14 of the menstrual cycle.
Unfertilised Egg
It is here in the fallopian tube that fertilisation will occur if sperm
is present. If fertilisation has not occurred the corpus Luteum stops
producing Progesterone, and the endometrium will start to shed around
day 28. The woman will then have a menstrual bleed.
Sperm production
Sperm is manufactured in the testicles which are located in the scrotum.
Sperm production takes approximately 80 days and is a continuous production
for most of an adult male’s life. Immature sperm cells start to
develop and grow in the seminiferous tubules. These tubules are connected
to the epididymis situated above the testes. It is here the developing
sperm pass into. The epididymis stores the sperm while it continues to
grow and in that growth starts to become motile. After approximately 2
weeks the sperm are mature. It is through masturbation or sexual intercourse
that they are released from the epididymis. During ejaculation the sperm
is pushed through to the urethra by contractions in the vas deferns. The
urethra provides the sperm with access out of the body via the penis.
The urethra also connects the bladder to the penis.
Male Anatomy
Fertilisation
Fertilisation occurs within the fallopian tube. Once the mature egg has
been released from the follicle it starts its journey down the fallopian
tube. During ejaculation, millions of sperm are released into the vagina.
Many will be trapped by the mucous in the vagina; however some continue
the journey through the cervix, into the uterus and up into the fallopian
tube.
The sperm try to penetrate the egg but only one sperm will penetrate
the zona (shell) of the egg. Once the zona has been penetrated, the sperm
will lose its tail. A chemical reaction takes place in the egg which prevents
other sperm from entering. Once fertilisation has occurred the egg is
known as a pronucleate egg.
Pronucleate Egg
The egg continues its journey towards the uterus. During this time it
is continually developing and changing, its cells multiplying. As this
process of cell division and changes occur the egg has now become an embryo.
The embryo does not implant into the uterine lining until approximately
5-7 days after fertilisation. By this stage the number of cells have multiplied
at such a rate that it no longer can be contained within the shell (zona)
of the egg, it has become a hollow ball of cells called a blastocyst.
The blastocyst then hatches out of the shell (zona) and implants into
the lining of the endometrium.
Hatching Blastocyst
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