Before oxytocin can exert its effects on the uterus, what must prime the uterus?

The correct choice highlights the role of estrogen and progesterone in priming the uterus for the effects of oxytocin. These two hormones are crucial in preparing the uterine tissues for the process of labor and delivery.

Estrogen is responsible for increasing the sensitivity of the uterine muscles to oxytocin, enhancing the efficacy of uterine contractions. This hormone is also key in promoting the growth of uterine tissue and the formation of oxytocin receptors, which are necessary for the subsequent actions of oxytocin.

Progesterone, on the other hand, helps maintain pregnancy by inhibiting uterine contractions during early gestation. As the body nears the end of pregnancy, the levels of progesterone begin to decline, allowing estrogen's stimulating effects to predominate. This shift creates an environment where oxytocin can effectively stimulate uterine contractions during labor, facilitating the childbirth process.

The combination of these hormonal actions effectively primes the uterus, making it responsive to oxytocin when labor begins. When these expected hormonal changes occur, the uterus is prepared and ready, ensuring that oxytocin can perform its vital role during the delivery of the offspring.