LACTOGENESIS: CHARACTERISTICS AND STAGES - BIOLOGY - 2025

The lactogenesis is the initiation stage of breast feeding, marking the end of differentiation of breast tissue. Thus, the glands begin with the secretion of milk, thanks to a process finely orchestrated by enzymes and hormones with regulatory functions such as prolactin, somatotropia, placental lactogen, corticosteroids, etc.

Temporarily, the first phase of lactogenesis occurs in the final stages of gestation, when the baby is nearing birth.

Mammals can produce milk to feed their young.

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This event is usually divided into two phases: I and II. The first includes all the changes necessary for the gland to acquire secretory capacities, while in the next phase the secretion of milk begins. Each phase has its characteristic hormonal and enzymatic profile.

characteristics

During pregnancy, females undergo a series of physiological changes that prepare them for the arrival of the baby. One of them involves the production of milk by the mammary glands - a phenomenon that only occurs in mammals.

When the female starts gestation, the mammary gland becomes a priority structure with regard to metabolism. This requires the provision of certain nutrients to be able to secrete milk effectively, such as water, glucose, different amino acids, lipids and minerals.

In this way, lactogenesis is the process by which the gland acquires the ability to secrete milk, and involves the maturation of the alveolar cells.

During the process, it can be seen that it increases blood flow to the glands. Also, receptors for certain hormones related to lactogenesis increase in number.

Before delivery (approximately the 5th or 6th month of pregnancy) a slight milky discharge is seen that increases precipitously and abundantly after the infant is born. Next we will explore the details of lactogenesis, in its two characteristic phases.

Stages

Lactogenesis comprises two stages: phase I that occurs during pregnancy and phase II that involves the onset of milk secretion after delivery.

Phase i

Phase I includes the onset of milk secretion and usually occurs 12 weeks prior to delivery. It is characterized by elevations in the concentration of lactose, immunoglobulins, and total proteins.

In addition, it reduces the concentration of sodium and chloride. Phase I is related to the production of colostrum or "first milk", a substance rich in immunoglobulins.

In this phase all the necessary modifications take place in the mammary gland to ensure its secretory capacity.

With the arrival of phase I, the endocrine profile of the mother is modified to promote milk synthesis. Among the hormonal changes, the action of prolactin stands out, a hormone with a leading role in the synthesis of the basic components of milk.

Glucocorticoids are associated with the diversion of nutrients, and thyroid hormones are responsible for sensitizing prolactin receptors.

Phase ii

The second phase of lactogenesis begins after delivery (usually within two to three days after giving birth) and is characterized by abundant milk production. The consecutive days can register 30 to 150 mL of milk per day, while after the fifth day the production can exceed 300 mL.

Blood flow to the mammary glands increases, as does the uptake of oxygen, glucose and citrate. Removal of the placenta after delivery results in a decrease in progesterone and other hormones.

Lactation is maintained by the removal of milk and by stimulation of the nipple, which causes the release of prolactin and oxytocin. The joint action of these hormones maintains the flow of milk.

It has been shown that stressful situations during labor can delay the onset of this second phase.

Milk maturation in phase II

During phase II, milk also experiences changes in its chemical composition. At this stage the milk is considered to have "matured". These changes involve an increase in the volume produced and the concentration of lactose, preceded by decreases in sodium, chloride ions and certain proteins.

After delivery, citrate, glucose, phosphate, and calcium levels increase. In addition, the pH of the secretion decreases - that is, its acidity increases.

Importance of breastfeeding

The best nutritional source that a newborn can obtain is undoubtedly breast milk from the mammary glands. The value of secreted milk goes beyond the mere nutritional content, since in its composition we find a complex set of antibodies, enzymes and hormones necessary for the development of the baby.

Breastfeeding is an action that carries multiple benefits - and not only for the baby, but also for its mother. The positive aspects of breastfeeding are found in the nutritional, environmental, physiological, and socioeconomic fields, among others.

For these reasons, the World Health Organization recommends a minimum breastfeeding period of six months - which can be extended at the discretion of the mother and the infant's needs.

Evolution of lactation

The emergence of adaptations during the course of evolution is a phenomenon that continues to impress biologists. In some cases, adaptations can evolve by combining unrelated parts, leading to amazing results.

An example of this is the evolution of an enzyme involved in breastfeeding in mammals: lactose synthetase.

The origin of this enzyme comes from modifications of two already existing enzymes - unrelated: galactosyl transferase, an enzyme of the Golgi apparatus; and alpha-lactalbumin, related to lysozyme, an enzyme that participates against defense against pathogens.

Thus, the union of two unrelated structures led to the generation of one of the most important adaptations of mammals.

Are only females lactating?

Lactation is a phenomenon that seems to be restricted to females. Despite the fact that the physiological machinery is present in the male sex and there are multiple ecological factors that could positively select male breastfeeding, it is a rare event in nature.

In old world bats, paternal lactation has been reported as a potential adaptive trait, unique among mammals. To date, the species with this very particular characteristic are Dyacopterus spadecius and Pteropus capistrastus.

References

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