Human Reproduction: Stages and Male Reproductive System

Human Reproduction

-Human reproduction is sexual and has two characteristics:

• The new individual is formed from a single cell, called a zygote.
• A zygote originates from the union (fertilisation) 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). 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. These prepare the individual to develop their sexuality and makes 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. 

The End of Reproductive Life

Ovaries normally stop functioning when women reach 50 years old. This provokes a series of physical and psychological changes that are 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 tubes. In the walls of the seminiferous tubes are the cells that produce sperm. In between these cells are cells that produce male sexual hormones (androgen).

• Epididymis: formed by the seminiferous tubes in each testicle. This is where sperm mature until they are ready for fertilization.
• Ductus deferens: is the continuation of the epididymis and ascends up to the interior of the abdomen. It¨s used to store sperm that remain there 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 2 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 glands. This is covered by a fold of skin known as foreskin.

• Seminal vesicles: these are located behind the bladder and flow into the ductus deferences. They secrete spermatic 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 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, and mucus lubricant formed in the Cowper gland.