Lactogenesis. Process by which transformations are operated that make the breast a secret organ.
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- 1 Features
- 2 Lactogenesis I
- 3 Lactogenesis II
- 4 Lactopoiesis
- 5 Sources
The next stage corresponds to Lactogenesis II, which occurs after childbirth and is characterized by a drop in progesterone levels and abundant milk secretion. It is then transited towards the lactopoiesis phase (continuous secretion of milk).
The regulation of milk production depends on central and local mechanisms. In general, the plants are in charge of the production itself, guaranteeing the differentiation and functioning of the mammary gland, while the locals are responsible for adapting it according to demand.
The central mechanisms are related to the activity of the different hormones that participate in the process. Local factors become important from the third day after delivery, when emptying the alveoli is essential for the continuity of milk production.
When pregnancy begins, from the first weeks, the breasts prepare for breastfeeding. Its size increases at the expense, fundamentally, of the growth of the duct system, verifying in the distal ends of these a widening and branching process.
Then, as pregnancy progresses, the branching rate decreases and the sac funds of each duct differentiate into alveoli, in which the typical epithelium of the ducts differentiates into secretory. The final part is organized into lobular units, formed by bouquets of alveoli that connect to a terminal conduit. Around the lobules there are capillary networks in which plasma cells abound, which are in charge of supplying milk with immuno-globulins.
Between 20 and 24 weeks, the functioning of the alveolar cells begins and secretions begin to accumulate in the alveoli and ducts. At this time, the breast is ready for milk production, producing minimal amounts of lactose and lactalbumin, which can be determined in blood and urine.
After delivery, the sensitivity of the nipple increases due to estrogenic fall, and as a consequence the oxytocin and prolactin release mechanism is activated . The abundant production of milk takes a few days. This stage, during which large volumes of milk are not yet produced, is called lactogenesis II.
The nipple becomes smaller, firmer and more prominent due to the suction that causes muscular contraction and venous stasis and is kept lubricated by the action of the Montgomery tubercles (sebaceous cells of the areola).
Prolactin is the hormone of greatest importance for the development of the mammary gland in the first months of gestation and during lactogenesis. It is attributed: to estrogens, the branching of the galactophoric duct system, to progesterone, the development of lobules and to prolactin, the functional differentiation of alveolar cells, an action that is blocked during pregnancy by placental lactogen and high amounts progesterone.
Prolactin and placental lactogen have common receptors in breast cells, but the lactogen has a greater affinity for them. Once the placental delivery occurs, the concentration of progesterone decreases and the lactogen disappears, creating conditions for prolactin to bind to breast receptors.
The concentration of prolactin increases progressively during gestation, to undergo a decrease, hours before delivery, after this, it increases again, coinciding with stimulation of the nipple, and if this does not occur, its numbers return to figures similar to the preconceptional ones in the course of 2 to 3 weeks.
In the case of nursing mothers, they decrease, but slowly, remaining higher than those of the prenatal stage, until 6 months after delivery. Its amounts increase during sleep, according to the circadian rhythm that follows its production, in which it is released in the form of pulses, variable in number and duration throughout the day.
The intense or simultaneous sucking of both nipples doubles the secretion of prolactin, although excesses should be avoided because they have been shown to deplete the response, causing the inverse effect if the interval is less than 2 h, which makes the relevance of feeding questionable. within those limits; however, it should be clarified that no relationship between prolactin levels and volume of milk secretion has been demonstrated in praxis.
To reach the outside, the milk must first pass through the smallest ducts, the light of which collapses as a consequence of the negative pressure produced by the suction, thus obstructing the alveolar emptying, but the contraction of the myoepithelial cells (oxytoxino-dependent ) that envelop them propel milk into larger gauge ducts where suction is effective.
Oxytocin is released in response to stimulation from the nipple, by suction or manipulation, and by other stimuli such as visual, sound and emotional, which reach the supraoptic and paraventricular nuclei of the hypothalamus through different routes. The hormone is carried to the breast by the blood, a continuous process throughout the intake and, thanks to which, the empty tubes are filled.
Other hormonal mechanisms that participate in the production of milk by the breasts are hormones, such as: insulin, corticosteroids, growth hormone and thyroid glands, which are necessary for the normal function of the mammary gland in its productive activity, although its relevance is not equal to that of prolactin. This explains why obese, insulin-dependent diabetic mothers or those who receive corticosteroid treatment before delivery suffer delayed lactogenesis.