What hormone is responsible for initiating lactation?

Prolactin is the hormone primarily responsible for initiating lactation. It is produced by the anterior pituitary gland and plays a crucial role in the development of mammary glands during pregnancy and the production of milk after childbirth. When a baby suckles at the breast, nerve endings in the nipple stimulate the release of prolactin, which leads to the synthesis of milk in the alveoli of the breast tissue.

As the levels of prolactin increase, it promotes the secretion of milk and continues to do so as long as breastfeeding occurs, ensuring that the infant receives adequate nutrition. This hormone's role is vital because without sufficient prolactin, milk production would be insufficient to support the infant.

Other hormones mentioned also play significant roles in the overall process of reproduction and lactation but do not initiate lactation. For instance, oxytocin is primarily involved in the milk ejection reflex, helping to expel milk from the breast after it has been produced. Estrogen and progesterone contribute to the development of breast tissue during pregnancy and prepare the body for nursing but are not the hormones that stimulate milk production.