In the book LACTATION Physiology, Nutrition, and Breast-Feeding (1983) by Neville and Neifert there are histology slides and electronmicrographs of the ductal system in a few different women who were deceased. One was a woman who died 48 hours after last nursing her child. Another was a nulliparous 15 y o. parenchyma are functioning elements; stromal are supportive framework "Prior to pregnancy, the mammary gland from the adult female is in an inactive state which permits easy identification of its parenchymal and stromal organization. ...the lobules consist of tubules or ducts lined with epithelium and embedded in a connective tissue stroma. They are widely separated and connective tissue and adipose tissue are the predominate elements. The interlobular connective tissue is dense, fibrous, and markedly less cellular than the intralobular connective tissue." "At this stage of development, there is only a scanty contribution from the glandular parenchyma. A few budlike sacculations may be seen arising from the ducts, but the gland consists predominantly of lactiferous, interlobar, and interlobular ducts. The larger ducts are lined by stratified cuboidal epithelium, except near the nipple where they are lined by stratified squamous epithelium." "The few alveoli present consist of simple cuboidal epithelial elements without distinctive morphologic features. They are virtually indistinguishable from the epithelium of the smaller ductal channels." "A point of importance ... is that the glandular parenchyma of the breast apparently does not respond to the hormonal environment in a totally synchronous fashion. Different areas within the same breast may change to greater or lesser degrees." "A modest, though discernible, degree of alveolar development occurs at the time of menarche, but with the advent of the hormonal changes of pregnancy, the mammary gland undergoes a spectacular phase of growth and proliferation. "The active phase is characterized by a rapid increase in the number of alveoli. Growth occurs at the terminal portions of the intralobular ducts which branch numerous times to end in alveolar sacculations. In the early trimester, the secretory alveoli are collapsed, but as gestation advances the saccules expand and enlarge, transforming the gland into a classic tubuloaveolar structure. "During the first few days after parturtion, a significant change occurs in the secretory elements of the mammary gland. Within the first 12 hours, the cells lining the alveolar sacculations become high cuboidal to columnar and develop classic cytologic characteristics of an exocrine cell. "Regular suckling stimulates the continuation of milk secretion. When this is stopped, the gland quickly ceases its activity and undergoes a relatively rapid phase of regression. Within a few days, the milk remaining in the alveolar lumina and ducts is resorbed. A steady decrease in parenchymal elements ensue with the concomitant reappearance of larger amounts of interlobular and interlobar connective tissue. The gland, however, does not regress to its original prepubertal state and many of the alveoli persist. "Within the alveolar epithelium a great amount of lysosomal and autophagic activity accounts for the initial regression of the epithelium." "The gland then remains in a resting condition until the advent of the next pregnancy wherein the developmental cycle of proliferation and secretion commences." "Near the menopause, but usually before true cessation of cyclic ovarian functions, the mammary gland and surrounding breast tissues begin to atrophy. Loss of tissue begins initially in the peripheral aspects of the lobe, but eventually almost all alveolar and interlobular ductal elements are lost " Part of their summary: "Prior to pregnancy the gland is composed primarily scattered ductal elements which drain into a series of collecting or lactiferous ducts. These ducts drain into the nipple. Upon appropriate hormonal stimulation, the mammary ducts develop numerous secretory alveoli which cyclically produce milk and empty their contents into the ductal system. Upon termination of suckling, a raid regression occurs in the alveolar and ductal trees with end stage involution occurring after the menopause. They do say most of this is "predicated on animal models as little information is available on the structure and functional morphologic changes seen in the human." Mardrey Swenson IBCLC *********************************************** The LACTNET mailing list is powered by L-Soft's renowned LISTSERV(R) list management software together with L-Soft's LSMTP(TM) mailer for lightning fast mail delivery. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html