Milksecreting

Milksecreting is the biological process by which the mammary glands produce and secrete milk for offspring. In mammals, lactation is initiated after parturition and is driven by hormonal changes that coordinate synthesis, storage, and delivery of milk to the nursing infant.

Anatomy and cells: The secretory units are alveoli lined with secretory mammary epithelial cells, surrounded by contractile myoepithelial cells. Milk is secreted into the alveolar lumen and drains through a network of ducts to the nipple. Contraction of myoepithelial cells, triggered by oxytocin, helps eject milk during feeding.

Physiology and regulation: Lactation progresses through stages. Prolactin stimulates the synthesis of milk components, while oxytocin triggers milk ejection. Lactogenesis I begins during late pregnancy with synthesis of milk constituents; lactogenesis II follows birth with rapid onset of copious secretion; maintenance lactation depends on regular milk removal. Estrogen and progesterone decline after birth, removing inhibitory effects on production. Additional factors such as insulin, cortisol, and growth hormone support ongoing milk production.

Milk composition and secretion: Milk contains lactose, casein and whey proteins, fats, minerals, vitamins, and immune factors such as secretory IgA. Lipids are secreted in droplets; proteins are released by exocytosis; water provides the bulk of volume. Composition adapts across the course of lactation and in response to infant demand.

Clinical and ecological notes: Milksecreting is a defining feature of mammalian reproduction, sensitive to maternal and infant cues. Variations in production affect infant nutrition. Disorders related to milk secretion include insufficient milk production, hyperprolactinemia, and galactorrhea, while lactation quality and quantity can be influenced by health, nutrition, and feeding patterns.