Final answer:
Colostrum is the first form of milk produced by the mammary glands postpartum, rich in immunoglobulins and essential nutrients, feeding the newborn until mature breast milk is produced.
Step-by-step explanation:
The yellowish watery fluid secreted by the mammary glands immediately after delivery, which the baby feeds on until the mother's milk comes in, is known as colostrum. It is secreted during the first 48-72 hours postpartum and is rich in immunoglobulins which play a key role in protecting the newborn against infections as they adjust to the nonsterile environment outside the womb.
This initial breast milk is not only high in protein but also features less fat and glucose compared to the mature breast milk that will be produced later on. As the baby suckles, oxytocin is released, stimulating myoepithelial cells to squeeze milk from the alveoli, providing the infant with these crucial nutrients and immune factors. Lactation is the process that continues beyond the production of colostrum, ensuring the infant receives adequate nutrition and hydration through foremilk and subsequent hindmilk during feedings.