After the umbilical cord stops providing nutrients, what causes a decrease in the neonate's plasma insulin levels?

The decrease in the neonate's plasma insulin levels after the umbilical cord stops providing nutrients is primarily linked to the activation of the hypothalamic-pituitary-adrenal (HPA) axis. Once the newborn is separated from the maternal blood supply, the immediate need for insulin diminishes as the source of glucose (from maternal circulation) is no longer available. The body responds by activating the HPA axis, which plays a critical role in regulating various physiological processes, including stress response and metabolism.

This activation leads to the secretion of stress hormones such as cortisol, which has an antagonistic effect on insulin and contributes to increased glucose production by the liver, helping to stabilize blood glucose levels in the absence of maternal nutrients. Consequently, as plasma glucose levels decrease without the umbilical supply, insulin production reduces, allowing the neonate to adapt to life outside the womb and begin to manage its own glucose homeostasis.

In contrast, other options do not directly correlate with the physiological mechanisms responsible for the decrease in plasma insulin levels in this scenario. For instance, the constriction of the umbilical cord does not inherently affect insulin levels since it is the cord's separation from maternal circulation that initiates these hormonal changes. Maternal hormone release has