The first stages of breast development are independent of sex hormones, but from the fifteenth week of gestation the breast area becomes temporarily sensitive to detosterone, which acts on the mesenchyme that condenses around epithelial cordonal areas, leaving the outline developed. mammary. If the detosterone does not follow a significant exposure, then the epithelial outlines are canalized, giving rise to the galaptophoric ducts in approximate number of 20 to 32. The branched alveolar tubule system, developed between the 32 and 40 weeks of gestation. Near birth, the fetal breast is affected by maternal placental steroids, giving a secretory change in the alveoli. At birth, maternal sex steroid hormones and prolactin stimulate colostrum secretion that can continue through the third or fourth week of age. Later, when maternal sex hormones and prolactin decline, the gland reverts to a simple ductal organization.
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