LACTOGENESIS
For successful lactation, three key events must transpire: (i) the prepartum proliferation of alveolar epithelial cells, (ii) the biochemical and structural differentiation of these cells, and (iii) the synthesis and secretion of milk components.
Lactogenesis, the initiation of lactation, entails a process of differentiation whereby mammary alveolar cells gain the capability to secrete milk. This process is delineated by a two-stage mechanism. The initial stage involves partial enzymatic and cytological differentiation of alveolar cells, accompanied by limited secretion. Subsequently, the second stage commences with a copious secretion of all milk components shortly before parturition, extending into the early postpartum period across most species. Elevated levels of progesterone during late pregnancy impede lactogenesis. However, a decline in progesterone levels near parturition facilitates the initiation of cell differentiation and lactation by the lactogenic complex. Estrogen exerts a stimulatory effect on prolactin (PRL) secretion. Glucocorticoids, upon becoming less bound to globulin proteins, form a complex with PRL, initiating differentiation and early enzymatic activities crucial for milk production and secretion. Additionally, hormones such as growth hormone (GH), insulin-like growth factor (IGF), insulin, and thyroid hormones play roles in this process. At the onset of lactation, alveolar cells undergo significant maturation of organelles like the rough endoplasmic reticulum, smooth endoplasmic reticulum, and Golgi apparatus under the influence of PRL and glucocorticoids. This maturation enhances the cellular capacity to synthesize and secrete proteins, fats, and lactose (Figure 22.5).22.13
Source:
Rana Tanmoy (ed.). Principles of Veterinary Animal Physiology. CRC Press,2026. — 290 p.. 2026
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