Re: Growth

Dear Adriana,

You asked why people stop growing when they become older.

Much of the growth (at least in height) is due to the lengthening of long bone, such as those of the thighs and legs. If you look at pictures of these bones, you'll see that they look like a long cylinder with a head at each end. The cylinder is known as the diaphysis (shaft) and the heads are known as the epiphyses. In an individual who is less than 20 to 21 years old, there is a thin piece of cartilage between the epiphysis and the diaphysis. This cartilage is known as the epiphyseal plate, which keeps getting thicker on the epiphyseal side.

As the cartilage plate is getting thicker on the epiphyseal side, special cells on the diaphyseal side remove parts of the cartilage and REPLACE it with bone. So the actual cartilage plate remains the same thickness as before, BUT bone was added to the diaphysis, lenthening it, thus making the person taller. As the person reaches 20 to 21 years of age, the cartilage stops becoming thicker, and the entire epiphyseal plate is removed by special cells. Once all of the cartilage is removed, the bones of the epiphysis and the diaphysis fuse with each other and the individual is no longer able to grow in height.

The process of thickening of the epiphyseal plate is controlled by "growth hormone' (also known as somatotropic hormone). This hormone, manufactured and released by cells of the pituitary gland (a small endocrine gland located at the base of the brain), enters the blood stream and goes to the liver. Here it tells the liver cells to produce and release a hormone known as "stomatomedins." Stomatomedins enter the blood stream and are conveyed to the epiphyseal plates and causes the cells of this cartilage to undergo cell division. The formation of new cartilage cells causes the epiphyseal plate to become thicker, and...well, you know the rest of the story.

I hope that this helps.

Leslie P. Gartner, Ph.D.
Department of Anatomy
Dental School
University of Maryland
Baltimore, Maryland