Physical changes that occur during puberty in girls

1. Development of breasts

Between the ages of 8-13 years, girls start developing breasts. Morphologically (that is in terms of form and shape), breasts look like a cone with the base at the chest wall and the apex at the nipple. It is possible that one of the breasts grows faster than the other but by the time the breasts are fully developed the differences in their shape and size are reduced. For a majority of girls there is a small difference in shape and size of the two breasts which is permanent and is totally normal. The size of the breasts and the time when it starts to grow also varies on an individual basis.

illustration of development of breasts during puberty in girls from age 7 to age 19 - Menstrupedia
2. Appearance of hair in the armpit

During puberty, hair begins to grow in your arm pits.

illustration of growth of hair in the armpits during puberty in girls from age 7 to age 19 - Menstrupedia
3. Widening of hips and appearance of pubic hair

Through the years of puberty, the hips of a girl widen and hair begins to grow in the genital region. Hair in the genital region is known as pubic hair.

illustration of widening of hips and growth of pubic hair during puberty in girls from age 7 to age 19 - Menstrupedia
4. Growth spurt

During puberty girls experience a sharp growth in their height. This is known as growth spurt. By the time she is 16 years old, she attains about 98% of the final height that she will eventually grow to.

illustration of growth in height during puberty in girls from age 8 to age 19 - Menstrupedia
5. Onset of menstruation

Menstruation is a process in which a sexually mature girl's or a woman's body releases of a small amount of blood and tissue through her vagina. Menstruation is a normal process that every healthy and sexually mature girl and woman undergo generally once every month. First occurrence of menstruation is called menarche and it marks the age when girls become sexually mature. Generally menarche occurs between the ages of 9 and 14 years and varies on an individual basis.

illustration of a girl looking at stain of blood on her underpants due to her periods - Menstrupedia
References:
  1. Teenage growth & development: 11-14 Years, http://www.pamf.org
  2. Puberty and adolescence, http://www.nlm.nih.gov
  3. Reproductive anatomy and physiology, http://www.columbia.edu