Sexual development involves enlargement, maturity, and the reproduction of the primary sex organs.  The male testes produce sperm cells and the prostate gland produces semen.  Males are can ejaculate the semen, which contains the sperm.  The female ovaries release the mature ova into the fallopian tubes. Menstruation occurs if conception does not.

As the primary sex organs mature, the secondary sex characteristics distinguish males from females.

In girls, the first physical signs of sexual development are the budding of breasts, usually between ages 8 and 13.  Not uncommonly, one breast may begin to develop before the other, or the breasts will be asymmetrical.  While this may seem a cause for concern, it usually is not a sign of abnormality. Breasts are seldom exactly the same size, and by adulthood they have usually evened out, so the differences are barely noticeable.  If the breasts remain markedly asymmetrical or, in rare instances, one fails to develop, it can be a source of embarrassment and sensitivity.  A visit to a physician may assure a girl with asymmetrical breasts that she does not have a disease, and that the problem can be surgically corrected.

The onset of menstruation does not necessarily coincide with the beginning of ovulation.  Many teenage girls experience irregular and/or very heavy periods for the first year or two—possible signs of absent or irregular ovulation.  This is not abnormal but a sign that while enough female sex hormones are being produced to cause a proliferation and shedding of the uterine lining, not enough pituitary stimulating hormone (FSH and LH) is being secreted to result in regular ripening and release of an egg from one of the ovaries. Within 1 or 2 years of menarche, however, most girls ovulate with some degree of regularity.

Male Sexual Development

Figure 2: Changes during puberty, in boys.  (A) shows a boy at about age 9 before the onset of puberty. In (B) secondary sex characteristics are beginning to develop; e.g., the beginning of pubic hair and enlargement of the penis and testes. There is also increased height and muscle development. (C) shows a fully developed male at about age 18.

Boys generally enter puberty about a year later than girls, i.e. between the ages of 10 and 14.  The first physical signs are growth of the testes and penis, accompanied or shortly followed by the appearance of pubic and other body hair.  About two years after puberty begins there is significant growth spurt - many 12-13 year-old girls are similar in size and weight to boys of the same age, but are then rapidly overtaken.  During the growth spurt, breast tissue may develop in up to two-thirds of adolescent boys, but this usually disappears in about 6 months (although in some it may persist for a year or longer).

Ejaculations generally begin sometime between the ages of 11 and 15, although anytime between the ages of 8 and 21 is considered normal.  Ejaculation may occur during sleep or in response to masturbation or a sexual fantasy.

Hormones and Adolescents

Males and Hormones:
At puberty a boy's testes start releasing large quantities of the androgen testosterone, which leads to muscle growth, body and facial hair, and other male sex characteristics.  Testosterone also contributes to gains in body size.  The production of hormones is associated with emotionality, specifically aggressive behaviour in boys.  These effects may be greatest when the endocrine system is being turned on.

Testosterone is responsible for the differentiation of the central nervous system (mainly the hypothalamus) into male and female types with regard to the different reproductive cycles and functions.  Males also receive major surges of testosterone at puberty so that the task of sex differentiation can be completed - oestrogen surges occur at that time in females.

Testosterone is responsible for the development of secondary sex characteristics in males such as pubic & facial hair, deepening of the voice, & ability to ejaculate sperm-laden semen.

Androgens are also responsible for baldness. 

Females and Hormones
Oestrogen is responsible for menarche & breast development.  Oestrogen released by a girl's ovaries cause the breasts, uterus, and vagina to mature and the body to take feminine proportions.  In addition, oestrogens contribute to regulation of the menstrual cycle.  Girls also are affected by androgens secreted by the kidneys for their growth spurt, underarm and pubic hair.  The production of hormones is associated with emotionality, both depressive and aggressive affects in girls.  These effects may be greatest when the endocrine system is being turned on.

How do Hormones affect adolescents and his/her transition into adulthood?
Despite the advance of feminisism and sexual equality, there is still (correctly or incorrectly) often perceived to be a great difference between the role of boys and girls, in the so called "Western Societies"  For boys, puberty is believed to expand role possibilities into the realm of work and achievement.  Girl's roles are believed to be confined, even on the eve of the 21st century a writer suggested: "Boys are classified as Doing and girls are classified as Being".  Girls may be more vulnerable to problems with autonomy, a sense of oneself as a separate self-governing individual, than boys may.  Girls have been characterized to be more emotionally focused and less individualized the identity status of self-chosen values and goals, from their mothers than boys do.  Girls are more interpersonal, intimate, and relationally focused.  Girls tend to be more intimate while boys may develop intimacy problems or become more salient at Puberty.  Emotional health, depression, conduct disorders, and eating disorders are all linked to gender.

A common belief is that pubertal change has something to do with adolescent moodiness and the desire for greater physical and emotional separation from parents.  Indeed, higher hormone levels are suspected to be related to greater moodiness, in the form of anger and irritability for males and anger and depression for females, between nine and fourteen years of age.  Studies indicate that low points of mood swings are associated with time spent with friends and in self chosen leisure and hobby activities while high points tended to occur in adult structured settings- class, job, school halls, school libraries, and church.  These finding suggest that situational factors may act in concert with hormonal influences to affect teenagers' moodiness.

Biological as well as social plays an important role.  Early maturation in boys appears at more of an advantage in many aspects of emotional and social functioning.  Adolescent boys are viewed as relaxed, independent, self-confident, and physically attractive.  Late maturing boys are viewed as anxious, overly talkative, attention seeking in behaviour.  Among girls the impact of early versus late maturation is just the opposite.  Early maturers are below average in popularity, appeared withdrawn and lacking in self-confidence, and held fewer positions of leadership roles.  Late maturers are regarded as physically attractive, lively, sociable and leaders in school.

In conclusion, it is safe to say that hormones and their effects on adolescents vary with age and gender.  Not every transition into adulthood will be easy, but to enhance and help adolescents cope with all the chemical changes taking place, one needs to be supportive, understanding, and patient to all trial and errors.

Brothers to Sisters
"Brothers who became sisters" was a hot topic in the Psychology press during the 1980s.  There is at least one recorded instance of three brothers becoming sisters.

While transsexual sisters are very rare, they are also far less rare than might be expected if we accepted (for example) that 1 in 2000 male babies suffer from gender dysphoria on a random basis.  Other biological and sociological factors seem to come in to play, and this remains a source of medical interest.

16 year old Kim Petras, formerly Tim.  Pictured just after her SRS, following four years of hormone treatment.

Effects of Hormone Treatment on the Transsexual Male-to-Female Boy/Girl
Ideally, in order to maximise the physical benefits, low level oestrogen treatment of the young transsexual boy-to-girl should begin at age 8-9 years.  Before the onset of male puberty (at about age 11, but can vary by 2 years) a bilateral orchiectomy (castration) should be performed to remove both testes and hormonal treatment then increased to induce a female type puberty age 10-11.  The results are usually extremely successful, with many clearly female aspects (e.g. limited muscle growth  and flattering fat deposits) resulting as the child moves to adulthood, whilst avoiding clearly male aspects (e.g. broken voice and facial hair).  However, even in this best possible case, it's impossible to totally overcome the combination of XY chromosomes and a hormonal legacy dating back to the womb, with typical results still being above average shoe size and below average bra size for a woman.  

For much more information about the female hormone treatment of the young transsexual see this article.