There is a specific chromosome that determines our sex. A man has an XY chromosome and a woman has an XX chromosome. There are other combinations (involving three chromosomes) but the Y chromosome is associated with being male. A boy inherits a Y chromosome from his father. So it is men who determine the sex of a baby. A baby’s sex has nothing to do with the woman who only has an X chromosome to offer.
These chromosomes determine whether the gonads in the embryo become the testes (for a boy) or the ovaries (for a girl). The gonads become the centres for the production of genetic material (egg or sperm).
Once the male’s testes start producing androgens (primarily male hormones such as testosterone), they drive further change, which is concluded at puberty. This process is called sexual differentiation.
We all start out in the womb with the same building blocks for the development of sexual anatomy regardless of our sex. A process called atrophy inhibits the development of the superfluous anatomy.
Both male and female embryos have Wolffian ducts. In a boy these ducts develop into the vas deferens (that connects the testes to the penis) as well as the other tubes required for ejaculation of semen. In a female embryo these Wolffian ducts waste away.
Equally every embryo (regardless of sex) has Müllerian ducts. In a girl these ducts develop into the uterus (womb) and the vagina (that leads into the womb). In a male embryo these Müllerian ducts disappear. These two sets of embryonic ducts determine our ultimate internal reproductive anatomy and consequently our sex.
By the end of month two of pregnancy, there are already differences between males and females. However, these differences are only on the inside. The external structures still look pretty much the same. Every embryo (regardless of sex) has a genital tubercle.
If exposed to testosterone, the genital tubercle elongates to form the penis. In the absence of testosterone, the genital tubercle forms a clitoris. The labioscrotal folds of the embryo become the scrotum (for a boy) and the labia (for a girl). This explains why, as a woman ages, the skin around her labia looks increasingly similar to the wrinkly hairy skin of the testicles.
A man’s genetic material (sperm) is produced regularly from his testes throughout his life (until old age). Sperm, together with other glandular secretions, are ejaculated from the penis. This ejaculate is called semen. A girl is born with her genetic material: immature eggs that are released from the ovaries into the uterus on a monthly schedule from puberty until sometime after her last period (called the menopause) in late middle age.
The male reproductive organs include the penis, the testes and the various glands (including Cowper’s gland and the prostate). The male sex organ is the penis. A man’s sex organ (penis) is separate from his internal reproductive anatomy (testes and glands). The penis is made up of the glans, the shaft and the internal organ. The penis has three main functions.
Firstly the penis enables men to urinate but only when flaccid. When a man is aroused, he has an erection. The penis becomes solid and juts out from the body at an angle of approximately 45 degrees. Inside there are two cylinder-shaped chambers called the corpora cavernosa that run the entire length of the penis. The arteries relax and open up to let more blood to flow in; at the same time, the veins close up, trapping blood within the corpora cavernosa. Muscles at the base of the bladder contract and close off the urethra so it is impossible for urine to be released during ejaculation.
Secondly the penis is the male sex organ and source of male orgasm. The sex organ is the only organ that is capable of producing an orgasmic response. When stimulated, in conjunction with a mental focus on erotic stimuli, the organ can give rise to muscle contractions in the lower pelvic area and highly pleasurable sensations in the brain. Except in young boys, orgasm is always coincident with ejaculation.
Thirdly the penis is involved in reproduction because of the spermatozoa (sperm for short) in a man’s ejaculate (semen). Before a man can ejaculate he must be aroused, which involves getting an erection. Thereafter he usually needs penile stimulation to ejaculate.
It is quite common and perfectly normal for the penis to be curved (sometimes sideways). This has no detrimental effect on either reproduction or sexual pleasure. The prostate lies at the base of the penis, just below the bladder. During male ejaculation, sperm is transmitted from the ductus deferens into the male urethra via the ejaculatory ducts, which lie within the prostate gland. It is possible for some men to achieve orgasm solely through stimulation of the prostate gland (e.g. during anal sex).
The relaxed penis can be any size, depending on ambient temperature. (Antony Mason 1998)