Breast

The breast is one of two prominences found on the upper ventral region of the torso of female and male primates. In females, it serves as the mammary gland, which produces and secretes milk and feeds infants. Both females and males develop breasts from the same embryological tissues. At puberty, estrogens, in conjunction with growth hormone, cause breast development. Males do not develop pronounced or physiologically matured breasts because their bodies produce lower levels of estrogens and higher levels of androgens, namely testosterone, which suppress the effects of estrogens in developing breast tissue. The breasts of females are typically far more prominent than those of males.

Subcutaneous fat covers and envelops a network of ducts that converge to the nipple, and these tissues give the breast its size and shape. At the ends of the ducts are lobules, or clusters of alveoli, where milk is produced and stored in response to hormonal signals. During pregnancy, the breast responds to a complex interaction of hormones, including estrogens, progesterone, and prolactin, that mediate the completion of its development, namely lobuloalveolar maturation, in preparation of lactation and breastfeeding. Upon childbirth, the alveoli are stimulated to produce and secrete milk for infants.