Final answer:
Progesterone is the ovarian hormone that reaches its highest concentration during the secretory phase of the menstrual cycle, as it plays a key role in preparing the endometrial lining for potential implantation of a fertilized egg.
Step-by-step explanation:
The ovarian hormone that reaches its highest concentration during the secretory phase is progesterone. \
Following ovulation, as part of the luteal phase of the ovarian cycle and the secretory phase of the menstrual cycle, the corpus luteum forms and produces both estrogen and progesterone.
While estrogen levels do increase to a steady level, it is the concentration of progesterone that is significantly elevated during this phase.
The secretory phase involves the endometrial lining of the uterus preparing for potential implantation, with progesterone inducing various changes such as increased blood flow and decreased uterine contractility.
If fertilization does not occur, the corpus luteum will degenerate, leading to a decrease in progesterone and the onset of menstruation.