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This is the process of physical changes by which a child's body becomes an adult body capable of reproduction. Puberty is initiated by hormone signals from the brain to the gonads (the ovaries and testes). In response,the gonads produce a variety of hormones that stimulate the growth,function,or transformation of brain,bones,muscle,skin,breasts,and reproduction organs. Growth accelerates in the first half of puberty and stops at the completion of puberty. Before puberty,body differences between boys and girls are almost entirely restricted to the genitalia. During puberty,major differences of size,shape,composition,and function develop in many body structures and systems. The most obvious of these are referred to as secondary sex characteristics.
PHYSICAL CHANGES
Pubic hair:pubic hair often appears on a boy shortly after the genitalia begin to grow. In girls,the first appearances of pubic hair is termed pubarche. The pubic hairs are usually first visible at dorsal(abdominal) base of the penis. The first few hairs are described as stage 2. Stage 3 is usually reacted within another 6-12 months,when the hairs are too many to count. By stage 4,the pubic hairs densely fill the "pubic triangle."Stage 5 refers to spread of pubic hair to the thighs and upward towards the navel as part of the developing abdominal hair.
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Body and facial hair
In the months and years following the appearance of pubic hair,other areas of skin that respond to androgens may develop androgenic hair. The usual sequence is: underarm(axillary)hair,perinal hair,upper lip hair,sideburn(preauricular)hair,periareolar hair,and beard area. As with most human biological processes,this specific order may vary among some individuals: Arm,leg,chest,abdominal,and back hair become heavier more gradually. There is a large range in amount of body hair among adult men,and significant differences in timing and quantity of hair growth among different racial groups. Facial hair is often present in late adolescence,but may not appear until significantly later. Facial hair continue to get coarser,darker and thicker for another 2-4 years after puberty. Some men do not develop full facial hair for up to 10 years after the completion of puberty.
Chest hair may appear during puberty or years after not all men have chest hair. Most men get it around their penis.
Voice change
Under the influence of androgens,the voice box,or larynx,grows in both sexes. This growth is far more prominent in boys,causing the male voice to drop and deepen,sometimes abruptly but rarely "over night", about one octave,because the longer and thicker vocal folds have a low fundamental frequency. Before puberty,the larynx of boys and girls is about equally small. Occasionally,voice change is accompanied by unsteadiness of vocalization on the early stage 3-4 of male puberty around the time of peak growth. Full adult pitch is attained at an average age of 15 years. It usually precedes the development of significant facial hair by several months to years.
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Male musculature and Body shape
By the end of puberty,adult men have heavier bones and nearly twice as much skeletal muscle. Some of the bone growth(e.g shoulder width and jaw) is disproportionately greater,resulting in noticeably different male and female skeletal shapes. The average adult male has about 150% of the lean body mass of an average female,and about 50% of the body fat.
This muscle develops mainly during the later stages of puberty,and muscle growth can continue even after boys are biological adults. The peal of the so-called " strength spurt",the rate of muscle growth,is attained about one year.
Often,the fat pads of the male breast and the male nipples will develop during puberty;sometimes,especially in one breast,this becomes more apparent and is termed gynecomastia. It is usually not a permanent phenomenon.
Body odor and acne
Rising levels of androgens can change the fatty acid composition of perspiration,resulting in a more "adult" body odor. As in girls,another androgens effect is increased secretion of oil (sebum) from the skin and the resultant variable amounts of acne. Acne cannot be prevented or diminished easily,but it typically fully diminishes at the end of puberty.
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