Human Reproductive System: From Puberty to Childbirth
Understanding the Reproductive Process
Fertilization and Early Development
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. The most important phase of fertilization is the union of the nuclei of the two gametes, the ovum and spermatozoon, contributing 23 chromosomes each. This new cell, the zygote, contains 46 chromosomes and will develop into a new being.
When fertilization occurs in the Fallopian tubes, the zygote begins to divide many times during its journey to the uterus. It then becomes implanted on the walls of the uterus, leading to the formation of the placenta. The embryo is surrounded by a membrane known as the chorion. When the chorion and endometrium become linked and strongly united, they form the placenta, the area of union between the embryo and the mother via the umbilical cord.
After three months of development, the embryo is referred to as a fetus. Nidation is the process of the embryo implanting on the walls of the uterus.
Stages of Childbirth
Childbirth, or parturition, occurs in three main stages:
- Dilation of the uterine neck: This begins with contractions of the uterine walls and dilation of the cervix. The contractions cause the rupture of the amniotic sac, releasing the amniotic fluid.
- Expulsion of the fetus: Contractions of the uterine walls and pressure from the abdominal muscles push the fetus through the vagina to the exterior.
- Expulsion of the placenta: Once the newborn is out, the umbilical cord is cut. Later, the placenta detaches from the uterine walls and is expelled along with other remnants.
Sexual Characteristics and Puberty
Primary and Secondary Sexual Characteristics
Primary sexual characteristics refer to the presence of specific genitalia:
- Female: Presence of female genitalia.
- Male: Presence of male genitalia.
Secondary sexual characteristics develop during puberty and are influenced by sexual hormones:
- Female: Development of pubic and underarm hair, redistribution of body fat, and development of mammary glands.
- Male: Development of facial hair (beard) and body hair, increased bone and muscle mass, and voice change.
Puberty is the period when these changes occur, affecting both the body’s appearance and function, as well as personality and social relationships.
Female Reproductive System
- Ovaries: Two almond-sized organs where ova mature and are released monthly. They also produce female sexual hormones.
- Fallopian tubes: Two channels connecting the ovaries to the uterus, where fertilization typically occurs.
- Uterus: A cavity that prepares for a fertilized ovum and houses the developing embryo during the nine months of pregnancy.
- Vagina: A flexible channel connecting the uterus to the exterior. It opens via the vaginal orifice, located behind the urethral orifice. These orifices are surrounded by skin forming the labia.
Ovulation begins at puberty, between 10 and 12 years old in girls, marking the start of the ovaries’ function in producing ova. Menopause occurs around age 50, when menstruation becomes irregular and eventually ceases.
Male Reproductive System
- Testicles: Organs that produce spermatozoa and male sexual hormones, housed in a skin sac called the scrotum.
- Epididymis: Structures located above the testicles where spermatozoa mature.
- Vas deferens: Small channels through which spermatozoa travel to the seminal vesicles.
- Seminal vesicles: Store spermatozoa and combine them with a fluid that serves as a vehicle and nutrient source.
- Prostate: An organ that produces a fluid similar to that of the seminal vesicles. Seminal fluid, prostate fluid, and spermatozoa together form semen.
- Urethra: A tube running from the bladder and seminal vesicles to the opening at the head of the penis.
- Penis: A spongy organ that deposits spermatozoa inside the vagina. The end of the penis is called the glans, covered by a piece of skin known as the prepuce.
Gametes: Spermatozoa and Ova
Spermatozoa are the male gametes, much smaller and more mobile than ova. They consist of a head and a tail and can survive for up to three days inside the female reproductive tract.
The ovum is the female gamete, a large cell with limited mobility. It retains its reproductive capacity for about 24 hours after being released from the ovary.