Final answer:
Lactation is the process of milk synthesis and secretion from the mammary glands after birth. Breast milk composition changes during the first days of lactation and within a single feeding. Colostrum provides immune defenses, transitional milk is a combination of colostrum and mature milk, and mature breast milk consists of foremilk and hindmilk.
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. Colostrum, the milk produced in the first few postpartum days, provides immunoglobulins that increase the newborn's immune defenses. Transitional milk follows colostrum and is a combination of colostrum and mature milk. Finally, mature breast milk is produced, which consists of foremilk and hindmilk. Foremilk quenches the infant's thirst, whereas hindmilk satisfies the infant's appetite.