Evidence suggests that milk removal or infant suckling are not needed for the programmed changes of lactogenesis, although it is possible that milk removal improves the efficiency of early milk secretion (Pang and Hartman, 2007). The control of lactogenesis is completely hormonal. During this time milk volume increases from about 50 to 100 mL per day to 500 mL per day, and transitional milk is produced, a descriptor for milk that is literally transitioning from colostrum to mature milk in composition (Neville et al, 2001). The hormonal support of adequate circulating prolactin and cortisol are both required, and other hormones, including insulin and thyroid hormone, likely play a supporting role. This phase, defined by the copious onset of milk secretion, is triggered by birth and the drop in progesterone associated with removal of the placenta. Lactogenesis II or secretory activation of the lactocytes, also known as the milk coming in, occurs shortly after delivery, usually between days 2 and 8. This initial glandular fluid is colostrum. At the end of gestation, the alveoli are filled with proteins, including secretory IgA and leukocytes and desquamated cells. During pregnancy, secretory differentiation of the mammary epithelial cells into lactocytes that have the ability to produce milk components occurs: this is known as lactogenesis I. The capability to secrete milk, or lactogenesis, begins by midpregnancy, although actual milk secretion does not occur at this time because of high circulating levels of progesterone (and probably estrogen). These findings have implications for hand expression of breast milk as well as for breast augmentation or reduction surgery. It now appears that the milk ducts branch close to the nipple, that their number is lower and more variable than previously believed, that most glandular tissue is close to the nipple, and that the lactiferous sinuses, which were thought to store milk, do not exist. Research using ultrasound technology has changed understanding of breast anatomy ( Figure 65-1) (Ramsay et al, 2005). During pregnancy, with the support of these hormones and others including prolactin and placental lactogen, breast glandular tissue further differentiates, and the alveolar epithelium proliferates and then becomes secretory. Mammogenesis, or breast development, begins during puberty with increased breast size due mainly to estrogen and lobuloalveolar development facilitated predominantly by progesterone.
The mammary gland is a highly evolved skin gland, and its rudiments are first seen during the 6th week in utero. Schanler, in Avery's Diseases of the Newborn (Ninth Edition), 2012 Anatomy and Physiology of Lactationīreast milk is produced by the mammary alveolar cells of the breast after childbirth.
Mitochondria also supply the carbon for the synthesis of nonessential amino acids.
The citrate in the mitochondria is a major source of carbon for fatty-acid biosynthesis. Mitochondria control some cellular metabolism through differential permeability to certain anions. As with other cells, the mitochondria are key to the respiratory activity of the cell. Mitochondrial proliferation has been observed in all cells with a high metabolic rate and high oxygen utilization.ĭuring the presecretory differentiation phase in late pregnancy and early lactation, each mitochondrion undergoes a type of differentiation in which the inner membrane and matrix expand greatly. Mitochondria are increased in the epithelial cell at the onset of the lactation process.
It is supplied by an increase in the size and function of the cell’s mitochondrial population. The alveolar cell population of the mammary gland must have a greatly expanded oxidative capacity during lactation. Lawrence, in Breastfeeding (Ninth Edition), 2022 Mitochondrial Proliferation