Normal functioning of the male and female reproductive systems depends on complex hormonal communication signals between the endocrine system and the sexual organs (ovaries in women and the testes in men).
Knowledge of the natural processes involved in the maturation of an egg in the woman and the production of sperm in a man helps to improve the understanding of the causes of infertility and the role current
Like most of the body’s systems, hormones direct the intricate processes involved in male and female fertility and three key hormones are responsible for controlling the reproductive systems and cycles in both sexes.
The first is gonadotropin - releasing hormone (GnRH), originally called luteinising hormone – releasing hormone (LHRH), secreted by the hypothalamus . The hormone stimulates the secretion of two gonadotropin hormones from the pituitary gland , these are luteinising hormone (LH) and follicle stimulating hormone (FSH).
These two pituitary gland gonadotropins are the key driving forces behind the development of sperm in a man and the maturation and release (ovulation) of a fertile egg in a woman.
The body must produce these hormones in the right amounts, in the proper sequence and at precisely the right times for ovulation and sperm production to occur. Imbalances due to insufficient amounts or the wrong
timing reduces the chance of conception.
Sperm production
LH is responsible for the production of the male hormone testosterone, which along with FSH is responsible for stimulating sperm production in the testicles (or testes).
The process of producing sperm, spermatogenesis, is a continuous one, and it takes about 72 to 74 days for a male ‘germ’ cell to develop into an active sperm. Several hundred million sperm are produced on a daily basis from a starting point of about eight times as many germ cells.
Spermatogenesis is most efficient at a temperature of 34°C, but is vulnerable to a number of factors. A high environmental temperature or a prolonged fever for example, can be seen to affect the quality of the matured sperm two to three months later. From the millions of sperm available each day, only a small proportion of them has full fertilising potential.
Sperm consist of two main parts, the head which has the crucial role of attaching to an egg and penetrating the outer membrane taking with it its genetic information, and the tail, which enables it to ‘swim’ the length of the female reproductive tract to reach an egg. Problems with any of these components will affect the fertilising power of the sperm.
Producing fertile eggs (oocytes)
Unlike men, women are born with about 400,000 immature eggs already in their ovaries. Each month between puberty and the menopause one egg, usually, fully matures and starts its journey down the fallopian tubes in the anticipation of fertilisation.
Menstrual cycle and fertility
There are three phases to a woman’s ‘monthly’ menstrual cycle, during which the mucus in the cervix becomes ‘sperm-friendly’, the lining of the uterus prepares for pregnancy, and an egg in one of the ovaries matures within a follicle (fluid-filled sac) before being released ready for fertilisation.
Stage one:
The first stage of the cycle is called the follicular phase and lasts for about two weeks. During this stage, the secretion of FSH rises, stimulating the development of an egg-containing follicle and the maturation of the egg within it.
The growing follicle secretes increasing amounts of the female hormone, oestrogen, which triggers changes in the lining of uterus (endometrium) and cervical mucus. The cervical mucus thins to allow sperm to pass through, and the endometrium thickens making it ideal for the implantation of a fertilised egg.
Stage two:
About 32 hours before an egg is ready to be released, the amount of oestrogen produced by the follicle peaks, causing the pituitary to secrete a spike of luteinising hormone. This surge in LH production causes ovulation, when the matured egg bursts out of the follicle and travels down the fallopian tube.
Stage three:
The remains of the follicle become a corpus luteum, which secretes a second female hormone, progesterone. This helps maintain the best conditions for pregnancy should the egg be fertilised, and is known as the luteal phase.
If the egg is not fertilised within about 72 hours the corpus luteum eventually degenerates, and the egg is expelled from the uterus along with the lining as part of menstruation around two weeks later.
Fertilisation and pregnancy
However, becoming pregnant is not always straightforward even for people without fertility problems. Humans are, comparatively, one of the least fertile creatures on earth, with only a 25 percent chance of conception each month.
This is due to the relatively short time within each cycle when a woman’s egg can be fertilised. The best time for fertilisation and pregnancy is around the middle of the menstrual cycle just before ovulation occurs.
Sperm can only live for around 48 hours in the female reproductive tract, and the egg needs to be fertilised within 72 hours following ovulation. Under normal circumstances only a few hundred of the 14 million sperm deposited naturally into the vagina during intercourse are able to reach the end of the fallopian tube where the egg can be fertilised.
After one sperm has successfully fertilised an egg, cell division begins and the fused cells become an embryo. About a week following ovulation the embryo finds itself in the uterus and implants itself into the endometrium. Successful implantation prevents the corpus luteum and endometrium from breaking down.
From here, a third gonadotropin, human chorionic gonadotropin (hCG), produced by the placenta that develops at the point of implantation, plays an important role in maintaining the pregnancy by stimulating the corpus luteum to continue to produce high levels of oestrogen and progesterone.
Like most of the body’s systems, hormones direct the intricate processes involved in male and female fertility and three key hormones are responsible for controlling the reproductive systems and cycles in both sexes.
The first is gonadotropin - releasing hormone (GnRH), originally called luteinising hormone – releasing hormone (LHRH), secreted by the hypothalamus . The hormone stimulates the secretion of two gonadotropin hormones from the pituitary gland , these are luteinising hormone (LH) and follicle stimulating hormone (FSH).
These two pituitary gland gonadotropins are the key driving forces behind the development of sperm in a man and the maturation and release (ovulation) of a fertile egg in a woman.
The body must produce these hormones in the right amounts, in the proper sequence and at precisely the right times for ovulation and sperm production to occur. Imbalances due to insufficient amounts or the wrong
Sperm production
LH is responsible for the production of the male hormone testosterone, which along with FSH is responsible for stimulating sperm production in the testicles (or testes).
The process of producing sperm, spermatogenesis, is a continuous one, and it takes about 72 to 74 days for a male ‘germ’ cell to develop into an active sperm. Several hundred million sperm are produced on a daily basis from a starting point of about eight times as many germ cells.
Spermatogenesis is most efficient at a temperature of 34°C, but is vulnerable to a number of factors. A high environmental temperature or a prolonged fever for example, can be seen to affect the quality of the matured sperm two to three months later. From the millions of sperm available each day, only a small proportion of them has full fertilising potential.
Sperm consist of two main parts, the head which has the crucial role of attaching to an egg and penetrating the outer membrane taking with it its genetic information, and the tail, which enables it to ‘swim’ the length of the female reproductive tract to reach an egg. Problems with any of these components will affect the fertilising power of the sperm.
Producing fertile eggs (oocytes)
Unlike men, women are born with about 400,000 immature eggs already in their ovaries. Each month between puberty and the menopause one egg, usually, fully matures and starts its journey down the fallopian tubes in the anticipation of fertilisation.
Menstrual cycle and fertility
There are three phases to a woman’s ‘monthly’ menstrual cycle, during which the mucus in the cervix becomes ‘sperm-friendly’, the lining of the uterus prepares for pregnancy, and an egg in one of the ovaries matures within a follicle (fluid-filled sac) before being released ready for fertilisation.
Stage one:
The first stage of the cycle is called the follicular phase and lasts for about two weeks. During this stage, the secretion of FSH rises, stimulating the development of an egg-containing follicle and the maturation of the egg within it.
The growing follicle secretes increasing amounts of the female hormone, oestrogen, which triggers changes in the lining of uterus (endometrium) and cervical mucus. The cervical mucus thins to allow sperm to pass through, and the endometrium thickens making it ideal for the implantation of a fertilised egg.
Stage two:
About 32 hours before an egg is ready to be released, the amount of oestrogen produced by the follicle peaks, causing the pituitary to secrete a spike of luteinising hormone. This surge in LH production causes ovulation, when the matured egg bursts out of the follicle and travels down the fallopian tube.
Stage three:
The remains of the follicle become a corpus luteum, which secretes a second female hormone, progesterone. This helps maintain the best conditions for pregnancy should the egg be fertilised, and is known as the luteal phase.
If the egg is not fertilised within about 72 hours the corpus luteum eventually degenerates, and the egg is expelled from the uterus along with the lining as part of menstruation around two weeks later.
Fertilisation and pregnancy
However, becoming pregnant is not always straightforward even for people without fertility problems. Humans are, comparatively, one of the least fertile creatures on earth, with only a 25 percent chance of conception each month.
This is due to the relatively short time within each cycle when a woman’s egg can be fertilised. The best time for fertilisation and pregnancy is around the middle of the menstrual cycle just before ovulation occurs.
Sperm can only live for around 48 hours in the female reproductive tract, and the egg needs to be fertilised within 72 hours following ovulation. Under normal circumstances only a few hundred of the 14 million sperm deposited naturally into the vagina during intercourse are able to reach the end of the fallopian tube where the egg can be fertilised.
After one sperm has successfully fertilised an egg, cell division begins and the fused cells become an embryo. About a week following ovulation the embryo finds itself in the uterus and implants itself into the endometrium. Successful implantation prevents the corpus luteum and endometrium from breaking down.
From here, a third gonadotropin, human chorionic gonadotropin (hCG), produced by the placenta that develops at the point of implantation, plays an important role in maintaining the pregnancy by stimulating the corpus luteum to continue to produce high levels of oestrogen and progesterone.