The breast is one of two prominences located on the upper ventral region of the torso of primates. In females, it serves as the mammary gland , which produces and secretes milk to feed infants. At puberty , estrogens , in conjunction with growth hormone , cause breast development in female humans and to a much lesser extent in other primates. Breast development in other primate females generally only occurs with pregnancy. Subcutaneous fat covers and envelops a network of ducts that converge on the nipple , and these tissues give the breast its size and shape.

The key parts of the female breast include:. At the onset of puberty, female reproductive hormones — particularly estrogen —guide breast growth. Normal changes in the breast during pregnancy can include firming, enlarged nipples, darker nipples, and stretch marks on the skin due to enlargement.

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