Final answer:
The composition of breast milk changes from colostrum after childbirth to mature milk around the tenth postpartum day. Foremilk is initially provided, which is watery and quenches thirst, while fatty, creamy hindmilk comes towards the end of feeding, satisfying the infant's hunger.
Step-by-step explanation:
The composition of breast milk changes significantly during the first few days after childbirth and also varies throughout a single feeding. Initially, after childbirth, the breast produces colostrum, which is rich in protein and provides important immunoglobulins that boost the newborn's immune defense. Colostrum is followed by transitional milk and then by mature milk from around the tenth postpartum day. During a feeding session, the initial foremilk is watery and translucent, rich in lactose and protein, mainly serving to quench the infant's thirst. As the feeding progresses, the composition shifts to the more opaque, creamy hindmilk, which is higher in fat content and serves to satisfy the infant's appetite and contribute to their energy needs.
Hormonal regulation plays a key role in the production and composition of breast milk. After childbirth, the hormone prolactin spikes for a short period after each feeding to stimulate milk production for the subsequent feeding.