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Gametes – also known as sexual or gametic cells – are the aploid cells to which reproduction of the species is entrusted. Gametes production is responsible for gonads, which are the primary sexual organs of the reproductive system of the human being. Human gametes are different from the gametes of the woman: male gametes are spermatozoa, while female gametes are egg cells. Sperm are the result of the spermatogenesis process. Egg cells, on the other hand, are the fruit of this process.
Gametes and gonads
Gametes (the singular gamete) are the cells that are needed for reproduction. In men, gametes are spermatozoa. In women, however, they are egg cells (ovocytes or oocytes). Known also with the expression of sexual cells or gametes, gametes are the result of gonadal activity.
Gonads are the primary sexual organs of the reproductive system (or genital apparatus) of the human being. They are endocrine glands, which have the important function of securing, in addition to gametes, sexual hormones, which play a key role in the development of secondary sexual characters and genital control. Man’s gonads are different from the woman’s gonads: male gonads are the testicles, while the female gonads are the ovaries (to the singular ovary but also ovary or ovary).
Summary of the role of male and female gonads
|Ovary||Estrogen Progesterone||Egg cells|
The terms ‘gamete’ and ‘gamete’ derive from the Greek word meaning ‘marrying’ or ‘joining’. The use of terms with this etymological origin is a clear recall of the reproductive function of the cells, to which the above terms refer. Unlike all the other human body cells (somatic cells), which are diploid, the gametes are aploid. In genetics, all cells that contain one copy for each chromosome (aploidia) are called aploid, while diploids are called all cells that contain two copies for each chromosome (diploid). In sperm, present chromosomes are actually half the chromosome of a man. Likewise, in egg cells, present chromosomes are actually half the chromosome of a woman. The aploid condition, which characterizes gametes, is essential for reproduction.
Spermatozoon is a very small cell whose size may vary between 5 and 7 micrometers. Its structure is particular and includes: a head containing the cell nucleus and acrosome, an intermediate portion rich in mitochondria and a tail, equipped with mobility and called scourge. The particular sperm morphology is crucial to the reproductive process, as it allows them to meet and melt with the egg cell within the female genital system.
With its 0.12 mm diameter, an egg cell is one of the largest cells in the human body, so that it is also possible to see it with a naked eye without the microscope support. The egg cell cytoplasm is rich in phospholipidic reserve materials, which serve to deal with the various steps to which it will be subjected and possibly fertilization.
Spermatogenesis and these are the terms that indicate, respectively, the process of formation and maturation of gametes in humans and the process of formation and ripening of gametes in the woman.
Meiosis characterizes both spermatogenesis and egg cells. Meiosis is that complicated division process, typical of eukaryotic organisms, at the end of which a diploid cell becomes aploid. In other words, subjected to meiosis, a cell with two copies for each chromosome becomes a single copy cell for each chromosome.
In a healthy male, testicles produce about 100-200 million sperm per day. With a duration of about 64 days, the sperm formation and maturation process begins in the seminal tubules of each testicle and continues in the epididymis. The stay in the epididymis is about 12 days and is essential to give the sperm the mobility that distinguishes them. Upon completion of the maturation process, spermatozoa are stored and ready for ejaculation. In the absence of ejaculation events, the sperm has a limited life within the testis. With the passing of time, in fact, they degenerate and are absorbed by the testes’ decomposing ducts. It should be pointed out that spermatogenesis is a continuous process, with its own production pace. This implies that within the testicles there is a continuous replacement of spermatozoa. In man, spermatogenesis begins with puberty. Before that, the testicles do not produce gametes.
In a healthy woman, the ovaries cause one egg cell to mature every 28 days (duration of ovogenesis). This process can be divided into three important moments, which in the temporal order from the first to the last are: the follicular phase, the ovulatory phase (or ovulation) and the lutheal phase. The follicular phase is the time when the ovaries, after a precise hormonal stimulation, produce and bring to maturity, within a follicle, the future egg cell. At this stage, the egg cell is named primitive egg cell or primitive oocyte.
The ovulation phase is the time when, as a hormonal stimulant other than the previous one, the egg cell that is now mature separates from the follicle (and the ovary) and nestles in the Fallopian tubes, ready to meet with any sperm. The lutheal phase is the time when the follicle becomes a lutheal body and, in the event of non-fertilization of the female gametes, menstruation occurs. Unlike man, where sperm production begins from puberty, the woman is already born with all the primitive egg cells, which in the course of life may participate at least in the first phase of the genesis.
In this regard, some interesting studies have shown that in a newly born female subject, the number of primitive oocytes is about one million and that in the course of life only 500 of them undergo the ovulation process. This means that 99.95% of the primitive oocytes present at birth go to degeneration, while only a small 0.05% is the protagonist of the ovulatory phase of the ovogenesis.
From the meeting and melting of a male gamete with a female gamete, a very special cell originates, called zygote. Zygote is the first cell of a new person or, if preferred, the cell from which the fetus begins to develop. Zygote formation process takes the name of fertilization. Generally, fertilization takes place in Fallopian tubes.
Zygote is a diploid cell. Its diploidy is the chromosome of the sperm and the egg cell chromosome kit. In other words, the zygote contains within its nucleus a copy of all the chromosomes of the father of the future unborn and a copy of all the chromosomes of the mother of the future baby. Immediately after its formation, zygote moves from the Fallopian tube – the canonical site of fertilization – to the uterus. Once in the uterus, it begins to divide (two or four originate from one cell) and progressively enlarge. After the first divisions, zygote takes the name of blastocysts. After about 8 weeks of zygote formation, blastocyst becomes what is commonly called a fetus.
For fertilization to take place, a spermatozoon has to reach the egg cell, located within the female genitalia, and penetrate. As anticipated, the ability to move and penetrate the sperm depends on its particular structure: the tail allows movement within the genitals, while the head and the enzymes contained in the acrosome allow the demolition of the two outer protective barriers of the egg cell (radial crown and translucent area). In fact – it is good to point out – spermatozoon entering the egg cell never acts alone, but uses other ejaculation spermatozoa to destroy the outer protective barriers of eggs. So, the large number of male gametes produced daily is only seemingly useless.
The Highlights Of Male And Female Gametes
Ovulation calculator: your key to pregnancy planning
Conception is possible only in a few days of a woman’s menstrual cycle. The period in which a sexual relationship can lead to a pregnancy is called a ‘fertile window’ and lasts for a maximum of six days. Fast fertility coincides with ovulation, i.e. when a mature ovum is released from the ovary, it moves along the Fallopian tube and is available to be fertilized. Even the days immediately preceding this event are favorable to conception, as they prepare the ‘ground’ for any pregnancy (pre-ovulatory phase).
When you want a baby, then one factor to consider is the timing of sexual relations with ovulation. To understand at what point is most likely the basic conception to be familiar with the trend of your menstrual cycle and to identify the fertile window in advance. To this end, it may be helpful to monitor the signs that precede ovulation and to evaluate the statistics of the previous cycles.
The female reproductive system, in addition to being responsible for the production and transport of egg cells, makes available all that is needed to start a potential pregnancy. Throughout the fertile age (from puberty to menopause), the female reproductive system meets every month with a number of important structural and functional changes (menstrual cycle). These changes are associated with periodic and regular changes in the secretion of hypothalamic, pituitary and ovarian hormones.
The beginning of each cycle, which lasts about 28 days, is characterized by menstruation, that is, a loss of blood and tissue from the surface of the uterine wall (endometrium). During the first part of the menstrual cycle, the endometrium changes and becomes insensitive, thus preparing to receive the egg cell in case it is fertilized. At the same time, the oocyte goes to mature processes, which end up with the expulsion from the ovary (ovulation). When no conception occurs, the uterine wall lining is flushed and expelled with menstrual flow. Otherwise, the fertilized egg cell nests into the uterus, where it finds the most favorable environment for its implantation and for the continuation of pregnancy.
Ovules ripen at different moments and are released from the ovaries at intervals of approximately 28 days (one per menstrual cycle). The release of egg cell from ovarian follicle, an event known as ovulation, is a prerequisite for fertilization and is normally performed 14 days before the beginning of the next menstrual cycle, about halfway through the cycle.
In each menstrual cycle, the most favorable time to conception coincides with ovulation and days close to that event. Generally, if the woman has regular cycles, this process occurs approximately every 28 days. After the beginning of menstruation, an oocyte takes an average of 14 days to mature adequately and, under the hormonal stimulus, escapes from the follicle that contains it to enter the Fallopian tube (or oviduct). Here, the egg cell can be fertilized by a spermatozoon of male origin.
Limited production of gametes
Ovules grow from a group of germ cells whose number is fixed at birth, about two to four million. The number of potential ovules decreases over the course of life, as most germ cells degenerate at some point in their development (the phenomenon is called atresia). In the life of a woman, there are about 400 egg cells that are released.
And about men? For the purpose of conception, the male reproductive system has a relatively simple task: to produce semen and to transfer it to the female apparatus during the act of coupling. The secretion of sex hormones in males is fairly constant and is not subject to cyclical variations that occur in females during the menstrual cycle. Semen production (spermatogenesis) lasts for an indefinite period after puberty, as spermatogons (undifferentiated sex cells from which mature sperm originate) are repeatedly subjected to mitosis. This ensures that the group of potential male gametes does not run out.
Ovulation and fertilization
Fertilization is the result of the combination of a paternal sperm with the maternal egg cell. From this union originates the zygote, a cell that in the space of 9 months develops and divides repeatedly to give birth to a child. We have seen how conception is possible only in a few days of a woman’s menstrual cycle. Indicatively, the period when the egg is fertilized starts 4-5 days before ovulation and ends 1-2 days later. This is possible considering that the egg cell matures when it is expelled from the ovary, survives for about 24 hours, while spermatozoa can remain vital in the female genital system up to 72-96 hours after the relationship. Within this ‘fertile window’ conception is more likely in the two days preceding ovulation and on the day that it occurs.
After ovulation, the menstrual cycle is completed by the lutheal phase, which runs from the 16th to the 28th day. The remains of the follicle that hosted the oocyte formed the so-called lutheal body, which produces progesterone. This hormone is important as it prepares the endometrium (i.e. the inner lining of the uterus) to receive the fertilized egg cell (plant) in case conception occurs.
If the oocyte is fertilized, it begins to sit and settle in the endometrium (at the blastula stage) 3 or 4 days after reaching the uterine cavity, i.e. 6-7 days after sexual intercourse. Conversely, if conception does not occur, from about 28th day menstruation appears, with the remains of the endometrium being expelled from the vagina.
Conception and pregnancy
For conception, male seminal fluid should be introduced into the female reproductive tract within five days prior to ovulation. The sperm moves through the cervical canal to the uterus, and, moving along the walls, they reach the fallopian tubes. Note: millions of spermatozoa that are deposited in the vagina, only one hundred normally reach the tubes while others die during the path.
The sperm moves towards the oocyte, which approaches them from the opposite direction. Consequently, conception, when it occurs, usually occurs in uterine tubes, most often in the distal tract (closer to the ovary).
The fertilized egg goes to a series of cell divisions and heads to the upper part of the uterus where it adheres and penetrates its wall (endometrium). This is how the so-called system works. After this event, the product development of conception continues, which increases in size and complexity. If fertilization is not successful, however, the plant does not occur and the egg cell fades within a few hours.
Although the duration of the menstrual cycle is different from the average of 28 days, it should be considered that the first stage of the menstrual cycle (estrogenic) is variable and may suffer oscillations, while the second stage (progestinic) is more constant and lasts an average of 14 days. To identify the fertile period in advance, it is possible to refer to some indicators of ovulation.
This particular moment of the menstrual cycle can be identified by various methods:
- Baseline temperature measurement.
- Observation of the cervical mucus.
- Monitoring of hormonal levels (ovulation testing).
To these fertility assessments, you can add some signals that can be associated with the cycle phases. With certain individual variables, ovulation may be associated, in particular, with abdominal pain, breast sensitivity, increased libido, vulvar swelling, backache (lumbar) and intermittent spotting.
Frequency of sexual intercourse
The calculation of ovulation is susceptible to error, as menstrual cycles may be influenced by many factors, and the most fertile period may be unexpectedly anticipated or delayed as expected. Success rates in conception increase especially two days before ovulation and the same day this occurs. It should be remembered that the life of the egg cell does not last for more than 24 hours, making conception after ovulation highly unlikely, while spermatozoa can remain vital for a longer and variable period (up to 5 days from the relationship).
In order to increase the chances of taking a pregnancy, it is important to have regular sexual activity. To have reports every 2 or 3 days, it covers the entire supposed fertile period as much as possible.