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Body Changes During Adolescence (External Changes)
The average girl reaches her mature height between the ages of seventeen and eighteen and the average boy, a year or so later. Boys and girls who were immunized during babyhood are usually taller, age for age, than those who were not immunized and who, as a result, suffered from more illness that tended to stunt their growth.
Weight changes follow a timetable similar to that for height changes, with weight now distributed over areas of the body where previously there was little or no fat.
The various parts of the body gradually come into proportion. For example, the trunk broadens and lengthens, and thus the limbs no longer seem too long.
Both male and female sex organs reach their mature size in late adolescence, but are not mature in function until several years later.
Secondary Sex Characteristics
The major secondary sex characteristics are at a mature level of development by late adolescence.
Body Changes During Adolescence (Internal Changes)
The stomach becomes longer and less tubular, the intestines grow in length and circumference, the muscles in the stomach and intestinal walls become thicker and stronger, the liver increases in weight, and the esophagus becomes longer.
The heart grows rapidly during adolescence by the age of seventeen or eighteen, it is twelve times as heavy as it was as birth. The length and thickness of the walls of the blood vessels increase and reach a mature level when the heart does.
The lung capacity of girls is almost at a mature level at age seventeen; boys reach this level several years later.
The increased activity of the gonads at puberty results in a temporary imbalance of the whole endocrine system in early adolescence. The sex glands develop rapidly and become functional, though they do not reach their mature size until late adolescence or early adulthood.
The skeleton stops growing at an average age of eighteen. Tissues, other than bone, continue to develop after the bones have reached their mature size. This is especially true of muscle tissue.
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