Lactation (the secretion of milk) occurs at the final phase of the reproductive process. Several hormones participate in mammogenesis, the differentiation and growth of the mammary glands, and in the production and delivery of milk. Lactogenesis is milk production by alveolar cells. Galac-topoiesis, the maintenance of lactation, is regulated by PRL. Milk ejection is the process by which stored milk is released from the mammary glands by the action of oxytocin.
Mammogenesis occurs at three distinct periods: embryonic, pubertal, and gestational. The mammary glands begin to differentiate in the pectoral region as an ectodermal thickening on the epidermal ridge during weeks 7 to 8 of fetal life. The prospective mammary glands lie along bilateral mammary ridges or milk lines extending from axilla to groin on the ventral side of the fetus. Most of the ridge disintegrates except in the axillary region. However, in mammals with serially repeated nipples, a distinct milk line with several nipples persists, accounting for the accessory nipples that can occur in both sexes, although rarely. Mammary buds are derived from surface epithelium, which invades the underlying mesenchyme. During the fifth month, the buds elongate, branch, and sprout, eventually forming the lactiferous ducts, the primary milk ducts. They continue to branch and grow throughout life. The ducts unite, grow, and extend to the site of the future nipple. The primary buds give rise to secondary buds, which are separated into lobules by connective tissue. These become surrounded by myoepithelial cells derived from epithelial progenitors. In response to oxytocin, myoepithelial cells will contract, and expel milk from the duct. The nipple and areola, which are first recognized as circular areas, are formed during the eighth month of gestation. The development of the mammary glands in utero appears to be independent of hormones but is influenced by paracrine interactions between the mesenchyme and epithelium.
The mammary glands of male and female infants are identical. Although underdeveloped, they have the capacity to respond to hormones, revealed by the secretion of small amounts of milk (witch's milk) in many newborns. Witch's milk results from the responsiveness of the fetal mammary
Antimüllerian Testosterone hormone
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.