Final answer:
The two hormones that are low during menstruation are estrogen and progesterone. These hormones drop when the corpus luteum degenerates, initiating the menstrual flow and starting a new menstrual cycle.
Step-by-step explanation:
The two hormones that are low when the female menstrual flow occurs are estrogen and progesterone. During the menstrual cycle, if no fertilized egg is implanted into the uterus, the corpus luteum degenerates, leading to a decrease in the levels of estrogen and progesterone. This decrease triggers the shedding of the uterine lining, known as menstruation, and marks the beginning of a new menstrual cycle.
After ovulation, if pregnancy does not occur, the corpus luteum, which forms from the ruptured follicle post-ovulation, stops functioning, resulting in lower levels of these hormones. The fall in progesterone specifically facilitates menstruation by causing the endometrial lining to break down.