Girls' bodies undergo gradual changes during puberty, analogous to but distinct from those experienced by boys. Puberty is the process of physical changes by which a child's body matures into an adult body capable of sexual reproduction to enable fertilisation . It is initiated by hormonal signals from the brain to the gonads -either the ovaries or the testes . In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones , muscle , blood , skin , hair , breasts, and sexual organs. Physical growth —height and weight—accelerates in the first half of puberty and is completed when the child has developed an adult body. Until the maturation of their reproductive capabilities, the pre-pubertal, physical differences between boys and girls are the genitalia , the penis and the vagina. Puberty is a process that usually takes place between the ages 10–16, but these ages differ from girl to girl. The major landmark of girls' puberty is menarche, the onset of menstruation, which occurs on average between ages 12–13.    
A more precise measure of the kidney function can be estimated by calculating how much creatinine is cleared from the body by the kidneys. This is referred to as creatinine clearance and it estimates the rate of filtration by kidneys (glomerular filtration rate, or GFR). The creatinine clearance can be measured in two ways. It can be calculated (estimated) by a formula using serum (blood) creatinine level, patient's weight, and age. The formula is 140 minus the patient's age in years times their weight in kilograms (times for women), divided by 72 times the serum creatinine level in mg/dL. Creatinine clearance can also be more directly measured by collecting a 24-hour urine sample and then drawing a blood sample. The creatinine levels in both urine and blood are determined and compared. Normal creatinine clearance for healthy women is 88-128 mL/min. and 97 to 137 mL/min. in males (normal levels may vary slightly between labs).