Library · Physiology
Breast development
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Until puberty, the breast is practically the same in girls and in boys: development is minimal and comparable in both sexes. What changes everything is the arrival of puberty in girls.
Then the breast epithelium, the layer of cells that forms the gland and that had been quiet until that point, pushes into the fatty tissue of the breast and makes it grow.
That growth is driven by two hormones with different jobs. Estrogen develops the system of lactiferous ducts, the tubes that milk will later come out of. Progesterone increases the number of lobular alveoli, the small sacs that form at the tips of those tubes.
Think of a tree of ducts that branches out and then sprouts clusters at the tips. This growth of the breast is called thelarche, and it is usually the first sign of puberty in girls, at around nine or ten years of age.
In brief
Breast development is minimal and comparable in both sexes until puberty.
Then the breast epithelium, quiet until that point, invades the fatty tissue and the breast grows.
Estrogen develops the lactiferous ducts, and progesterone increases the number of lobular alveoli at their ends.
A tree of ducts that branches out and then sprouts clusters at the tips.
Thelarche, that growth, is usually the first sign of puberty in girls, at around nine or ten years of age.
Sources (3)
- National Center for Biotechnology Information, StatPearls PublishingAnatomy, Thorax: Mammary Gland, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingHistology, Mammary Glands, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Puberty, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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