Eva is 8 years old, and throughout her childhood, every bone, muscle, and sinew is continually lengthening in a coordinated fashion.

And what determines how tall she, and all of us, grow starts not in our bones, but in the brain.

From a pea-sized gland known as the pituitary, growth hormone is released throughout our lives. Growth hormone plays a number of important roles in the adult body,

including the regulation of our metabolism and the ability to maintain steady blood glucose levels. But during childhood, as high levels of growth hormone surge through our entire body, it has a far greater effect.

Traveling through the bloodstream, it stimulates the liver to produce an insulin-like chemical, growth factor-1. This causes muscle and cartilage cells to multiply; it's the secret behind how tall we grow.

At the ends of the long bones of our arms and legs are the epiphyseal plates, or growth plates,

soft disks made of cartilage. And it's here that growth factor-1 works its magic

by stimulating the cartilage cells into rapid division. These new cells push the older cells toward the center, where they harden,

gradually elongating the bone and making us taller.

The secret behind long bone growth - The Human Body: Secrets of Your Life Revealed - Grow - BBC

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The secret behind long bone growth - The Human Body: Secrets of Your Life Revealed - Grow - BBC

The secret behind long bone growth - The Human Body: Secrets of Your Life Revealed - Grow - BBC

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