Human Reproduction: Organs, Processes, and Stages
Human Reproduction
Human reproduction is sexual, so it needs the formation of gametes. The male gamete is the spermatozoon, and the female gamete is the ovum. The gametes are formed in specialized organs, which are called the testicles and the ovaries. The union of these cells is required for reproduction, which is fertilization, that gives rise to the forming of an egg cell or zygote, which forms the embryo in the uterus. This begins the period of pregnancy, which ends in the birth of the new being.
Characteristics of Human Reproduction
Primary Sexual Characteristics
- The existence of female genitalia in the female.
- The existence of male genitalia in the male.
Secondary Sexual Characteristics
Appear with maturity.
- In females: The development of pubic hair and hair under the arms, the distribution of body fats, and the development of mammary glands.
- In males: The development of pubic hair, the beard, and hair over a large part of the body, an increase in bones and muscles, and a change of voice.
These changes occur in puberty and they are the result of the action of sexual hormones.
Female Organs
Ovaries
Two organs. Inside them, each month, an ovum matures and is then released. Here the female sex hormones are produced.
Fallopian Tubes
These are two channels that join the ovaries to the uterus. Here fertilization takes place.
Uterus
A cavity that is prepared for a fertilized ovum and for housing the embryo. It can develop during the pregnancy.
Vagina
It’s a flexible channel that communicates the uterus with the exterior. The vagina opens to the exterior via the vaginal orifice, behind the urethral orifice. A skin surrounds these are internal lips, labia minora, and external lips which cover these, known as labia majora. At the upper part of the lips is the clitoris, a small sensitive protuberance.
Male Organs
Testicles
These are the organs that make the spermatozoa and the male sexual hormones. They are housed in a sack of skin known as the scrotum.
Epididymis
Structures located above the testicles and it’s where spermatozoa mature.
Vas Deferens
Small channels through which the spermatozoa travel to the seminal vesicles.
Seminal Vesicles
Here the spermatozoa are stored and they join together with a fluid that serves as a vehicle and food.
Prostate
An organ that makes a fluid that is similar to the seminal vesicles fluid. Both fluids with the spermatozoa make up the semen.
Urethra
The tube that runs from the bladder and seminal vesicles to the opening at the head of the penis.
Penis
A spongy organ whose function is to deposit the spermatozoa inside the vagina. The end of the penis is the glans, which is covered by the prepuce.
The Reproductive Cells
The Ovum
It’s the female gamete. It’s a very large cell and moves with great difficulty. It contains its reproductive capacity for 24 hours once it has been released. One ovum leaves the ovary, it goes to the fallopian tube where it stays for a short period.
The Spermatozoa
They are the male gametes. They’re much smaller and more mobile than the ovum. In their natural state, they are formed by a large part known as the head and a smaller part known as the tail. The spermatozoa can live about 3 days inside the female genitalia system.
Menstrual Cycle
Sex Hormones
The hormones produced by the ovaries and testicles cause the physiological changes which are responsible for the appearance of the sexual characteristics which differentiate men from women. These hormones are the sexual hormones, there are two kinds:
- Estrogens: which are the female sex hormones that are produced in the ovary.
- Androgens: which are the male sex hormones, produced in the testicles.
Changes During Puberty
Between 10 and 12 years in girls, the process of maturity begins in the ovaries, which begin their functions and produce ova. It begins the formation of sexual hormones by the ovary, beginning the cyclical functioning of ovaries, the control of the menstrual cycle, and the appearance of the secondary sexual characteristics. In males, maturing of the testicles, formation of male sexual hormones, and development of secondary sexual characteristics. Puberty is the time of life when all these changes are produced. The changes affect the appearance and functioning of the body and personality with others. Menopause is when the menstruation becomes very irregular and finally disappears.
Menstrual Cycle
During the maturity of an ovum, the uterus prepares for a possible pregnancy, that is where the fertilized ovum would be installed. The layer of mucus of the uterus is the endometrium. When the ovum is mature, it leaves the ovary and passes along the fallopian tube, it has a life of 24 hours. If it isn’t fertilized by a spermatozoon, the ovum dies. The endometrium is released 14 days after the death of the ovum. Contraception control is the way of preventing coitus from leading to pregnancy, interfering in any one of the mechanisms which produce it.
Fertilization
Fertilization is the union between an ovum and a spermatozoon to form an egg cell or zygote from which a new individual will be formed. It takes place in the fallopian tube during the trajectory towards the uterus. The spermatozoa are introduced into the vagina during coitus (ejaculation occurs). If spermatozoa find an ovum they surround it and try to penetrate it. Only one will achieve this. The most important phase of fertilization is the union of the nucleus of the two gametes. With this union, the paternal genetic information in the 23 chromosomes is mixed. This new cell is the zygote, which contains 46 chromosomes and from which the new being will be formed.
Pregnancy
When fertilization has occurred in the fallopian tube, the zygote begins to divide many times during its route to the uterus. This is the embryo and it becomes implanted on the walls of the uterus with the formation of the placenta. The embryo develops for 3 months, from this time is the fetus. The implantation of the embryo on the walls of the placenta is known as joining. It occurs 7 days after fertilization. The embryo is surrounded by a membrane, the chorion, which grows and penetrates the endometrium. They are strongly united forming a structure, the placenta, which is the area of union between the embryo and the mother. The embryo and fetus receive oxygen and nutrients for growth along the umbilical cord.
Birth
It occurs at the end of pregnancy. 3 stages:
- Dilation of the Uterine Neck: It begins with the contractions of the walls of the uterus and the dilation of the neck of the uterus. The contractions cause the rupture of the bag of amniotic fluid where the fetus develops during pregnancy and the amniotic fluid escapes.
- Expulsion of the Fetus: The contractions and pressure of the abdominal muscles push the fetus along the vagina to the exterior.
- Expulsion of the Placenta: The umbilical cord is cut. The placenta is released from the walls of the uterus and is expelled together with the other remains.