I AM ONE OF THE most visible signs of womanliness. But today many think of me as little more than a cosmetic appurtenance, a prop for the female ego. I am considerably more than that. My real reason for being is that I am capable of baffling, almost miraculous chemical conversions. I change blood into milk.
I am your left breast. (As in most women, the left is slightly larger than the right.) At one time, the very survival of the human race depended on me. For your primitive women ancestors, pregnancy was the normal state; baby followed baby. Breasts produced milk almost continuously during the childbearing years and even after those years were over. A granny could put to her breast the infant of a woman who had died, and soon there would be milk.
In actuality, I am nothing more than a modified, and infinitely complex, sweat gland. For the first few days after you were born I functioned. Hormones from your mother stimulated me into producing a few droplets of "witch's milk." (So, when they were born, did the boy's breasts.) Then the hormones' effect wore off and I went to sleep. Until you were about 12 I was dormant. Then the magic wand of the hormones was waved. Your ovaries matured, and under the prod of their hormones I started developing. (Breasts started to developing among your friends as early as eight years or as late as 18 years.) Fat deposits - I am mostly fat - were laid down. I swelled. My nipple grew, and my areola, the halo around it, took on a heavier pigmentation.
My glandular structure is by far my most interesting component. I have 17 independent milk-producing units. Some women have more, some fewer. Each is shaped something like a berry bush. The berries are my tens of thousands of microscopic alveoli. The invisible droplets of milk they produce feed into the branching ducts and finally into the main stem. The 17 stems terminate in my nipple. My fat coat provides protection and insulation for these delicate structures. I also contain connective tissue to bind me together; strands of this attach to your chest wall - kind of internal bra.
I am under almost total control of hormones. Prior to menstruation, they make me swell and I become more sensitive. My really big moment came, with the first pregnancy, when hormones from the placenta - which links baby and womb - awakened me. The hormone estrogen stimulated growth of my milk-duct system, and progestin prodded development and proliferation of my berrylike alveoli. Blood vessels, too, expanded their networks. Blue veins on my surface became visible. My weight doubled. As birth neared, I began a big housecleaning job. Until then, my alveoli had been filled with hard cellular material. It was necessary to dissolve this and make room for milk.
When you were born, a new hormone came into production: prolactin, manufactured by the pituitary gland on the underside of your mother's brain. This remarkable hormone starts my milk on its way.
For the first four days after birth, I secreted a yellowish, watery fluid: colostrum. There was very little nourishment here for you as a baby. You lost weight, and your Mother fretted. But I knew what I was doing. The colostrum helped clear the baby's digestive tract of mucus and other debris. Further, in my case, it was rich in antibodies to protect the newborn from diseases that might be deadly - such things as measles, whooping cough, scarlet fever, which you had as a child. By the fifth day after birth, you had been cleansed internally and were ready for real nourishment. And I was ready with the perfect food.