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When A Woman Is Lactating, How Does Her Body And/or Mammary Glands Make Milk?

When A Woman Is Lactating, How Does Her Body And/or Mammary Glands Make Milk?


Lactation is the process of milk production and secretion from the mammary glands of the postpartum female breast in response to a newborn suckling at the nipple. Breast milk offers optimum nutrition and passive immunity for the child, produces a significant metabolic boost in the mother, using the fat reserves acquired during pregnancy, and stimulates moderate uterine contractions to restore the uterus to its pre-pregnancy size (i.e., involution).

Structure of the Lactating Breast

Sweat glands have been changed to become mammary glands. The breasts of non-pregnant and non-lactating women are largely made up of adipose and collagenous tissue, with mammary glands accounting for just a small fraction of breast volume. Lactiferous ducts transport milk from the mammary gland and swell and branch significantly during pregnancy in response to oestrogen, growth hormone, cortisol, and prolactin. Furthermore, clusters of breast alveoli sprout from the ducts and grow outward toward the chest wall in response to progesterone. Breast alveoli are milk-secreting cuboidal cells. They are also known aslactocytes, that are surrounded by a net of contractile myoepithelial cells in a balloon-like shape.

Lactocytes secrete milk, which fills the alveoli and is pressed into the ducts. Lobules are clusters of alveoli that drain to a common duct; a breastfeeding female’s nipple has 12–20 lobules arranged radially around it. Lactiferous ducts drain milk into lactiferous sinuses, which meet at 4 to 18 holes in the nipple, known as nipple pores. Montgomery glands are tiny lumps on the areola (the darker skin surrounding the nipple). They produce oil to keep the nipple opening clean and prevent the nipple from chapping and breaking during nursing.

The Process of Lactation

Prolactin, a pituitary hormone, is necessary for the development and maintenance of breast milk production. It is also necessary for the mobilisation of maternal micronutrients for the production of breast milk. The amount of circulating prolactin begins to rise about the fifth week of pregnancy, eventually reaching 10–20 times the pre-pregnancy concentration. Prolactin and other hormones prepare the breasts anatomically for milk secretion during pregnancy, as we said previously. Late in pregnancy, the level of prolactin reaches a plateau high enough to start milk production. During pregnancy, however, oestrogen, progesterone, and other placental hormones suppress prolactin-mediated milk production. This restriction is not lifted until the placenta is ejected, and milk production begins.

The baseline prolactin level declines dramatically after delivery, but it is restored for a 1-hour surge at each feeding to encourage milk supply for the following meal. Estrogen and progesterone levels rise modestly with each prolactin surge. Sensory nerve fibres in the areola activate a neuroendocrine response that causes lactocytes to secrete milk into the alveoli when the newborn sucks. The posterior pituitary secretes oxytocin, which causes myoepithelial cells to squeeze milk from the alveoli, allowing it to drain into the lactiferous ducts, accumulate in the lactiferous sinuses, and exit via the nipple pores. From the moment a newborn starts sucking (the latent period) until milk is produced, it takes less than a minute (the let-down). The let-down reflex’s positive feedback loop is depicted in the diagram below.

Milk synthesis mediated by prolactin varies throughout time. Breastfeeding (or pumping) on a regular basis will keep circulating prolactin levels high for several months. Even if you continue to nurse, your baseline prolactin level will drop to its pre-pregnancy level over time. Growth hormone, cortisol, parathyroid hormone, and insulin, in addition to prolactin and oxytocin, aid breastfeeding by promoting the transfer of maternal amino acids, fatty acids, glucose, and calcium to breast milk.

Changes in the Composition of Breast Milk

Colostrum, a thick, yellowish material strong in protein but lower in fat and glucose than mature breast milk, fills the alveoli in the latter weeks of pregnancy. Some women have colostrum leaking from their nipples before giving birth. Mature breast milk, on the other hand, does not leak throughout pregnancy and does not begin to secrete until several days following delivering. Colostrum is produced in the first 48–72 hours after birth. Only a little amount of colostrum is generated in a 24-hour period—roughly 3 ounces—but it is enough for the baby in the first few days of life. As the infant adapts to a nonsterile environment, colostrum is rich in immunoglobulins, which impart gastrointestinal and possibly systemic immunity.

The mother secretes transitional milk during the third postpartum day, which is a cross between mature milk and colostrum. From about postpartum day 10 onwards, mature milk is produced. Cow’s milk is not a substitute for breast milk, as seen in the table below. It has less lactose, fat, and is higher in protein and minerals. Furthermore, the proteins in cow’s milk are difficult for an infant’s digestive system to process and absorb due to its immaturity.

To learn more about lactation and other such interesting topics in biology, check Human Reproduction – 1 From Class12 Biology.It would be possible to get all queries cleared in the best way with the help of the learning resources.

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