Final answer:
Lactation is the process of milk synthesis and secretion in response to infant sucking. Breast milk composition changes from colostrum to transitional milk to mature breast milk. Foremilk quenches thirst, while hindmilk satisfies appetite.
Step-by-step explanation:
Lactation is the process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to an infant sucking at the nipple. Breast milk provides ideal nutrition and passive immunity for the infant, encourages mild uterine contractions to return the uterus to its pre-pregnancy size (i.e., involution), and induces a substantial metabolic increase in the postpartum person, consuming the fat reserves stored during pregnancy.
The composition of breast milk changes during the first days of lactation and in the course of a single feeding. In the first few days after giving birth, the milk produced is called colostrum, which is high in protein and contains immunoglobulins that boost the newborn's immune defenses. As lactation progresses, the milk transitions to transitional milk and then to mature breast milk, which is nutritionally balanced and changes from the beginning to the end of a feeding. The initial milk released during a feeding, called the foremilk, quenches the infant's thirst, while the milk released later in the feeding, called the hindmilk, satisfies the infant's appetite.