Human Reproduction: Stages and Systems
Human Reproduction Characteristics
Human reproduction is sexual and has two main characteristics:
- The new individual is formed from a single cell, called a zygote.
- A zygote originates from the union (fertilization) of two gametes or sex cells.
Humans have two kinds of gametes: sperm and ova. Men produce sperm, and women produce ova.
Puberty
Puberty begins in men with the first ejaculation (spermarche) and in women when the first menstruation takes place (menarche). This process is regulated by Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). Puberty lasts around 3 to 4 years:
- Girls: 10–13 years old
- Boys: 12–14 years old
Adolescence
During this stage, many physical and psychological changes occur, preparing the individual to develop their sexuality and making them capable of reproducing.
- Women: These changes are a consequence of the release of ova and sexual hormones (estrogen and progesterone) from the ovaries.
- Men: These changes are a consequence of the release of sperm and sexual hormones (testosterone) in the testicles.
End of Reproductive Life
Ovaries normally stop functioning when women reach 50 years old. This provokes a series of physical and psychological changes known as the menopause (for women) and the andropause (for men).
The Male Reproductive System
The male reproductive system is formed by the testicles, penis, reproductive tract, and the male accessory glands.
Testicles
The testicles are the organs that produce male gametes or sperm. They are oval in shape and are constituted of several rolled seminiferous tubules. In the walls of the seminiferous tubules are the cells that produce sperm. In between these cells are cells that produce male sexual hormones (androgen).
- Epididymis: Formed by the seminiferous tubules in each testicle. This is where sperm mature until they are ready for fertilization.
- Ductus deferens: This is the continuation of the epididymis and ascends up to the interior of the abdomen. It is used to store sperm until they exit the body.
- Urethra: This duct is also part of the urinary tract, connecting the bladder to the exterior. The end of the urethra is located inside the penis.
Penis
The penis is the male copulatory organ. It is formed by two spongy tissues known as corpora cavernosa, which are located on top of the urethra. The urethra is surrounded by another layer of tissue, corpus spongiosum, that widens at its end, forming the glans. This is covered by a fold of skin known as the foreskin.
Accessory Glands
- Seminal vesicles: These are located behind the bladder and flow into the ductus deferens. They secrete seminal fluid containing glucose, a nutrient for sperm.
- Prostate: Located below the urinary bladder. This secretes prostatic fluid, which consists of substances to protect sperm from the acidity of the vagina.
- Cowper glands: A pair of glands located at the base of the penis. Their function is to secrete a lubricating fluid that facilitates sexual intercourse.
Semen Composition
SEMEN is the fluid that contains the spermatozoon. It constitutes 10% of the secretion; the other 90% is composed of:
- Nutrients for sperm, formed in the seminal vesicles.
- Neutralizing substances produced by the prostate.
- Mucus lubricant formed in the Cowper gland.