Pediatric emergency medicine trisk 1546 1546
Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (75.45 KB, 1 trang )
early teenage years, the menstrual cycles may be irregular due to immaturity of
the hypothalamic–pituitary–ovarian axis. Occasionally, an adolescent girl is
brought to the ED by her parents to confirm their belief that she is having her first
menstrual period. About 65% of girls are in sexual maturity stage 4 (Tanner stage
4) for breast development when menarche occurs ( Table 79.1 ). Of the remaining
girls, about 25% are in breast development stage 3 and 10% are in stage 5. If the
adolescent’s chronologic age and degree of pubertal development are consistent
with this expected pattern of maturation, no further evaluation is necessary.
The normal menstrual cycle is divided into three phases based on the
physiologic processes occurring in the ovary and uterus. The ovarian cycle
consists of the follicular phase, ovulation, and luteal phase, whereas the uterine
cycle is divided into menstruation, proliferative phase, and secretory phase. By
convention, the cycle is counted in days beginning with the first day of bleeding.
During the follicular phase, ovarian follicles are stimulated by the release of
pituitary follicle-stimulating hormone (FSH), one or two of the follicles become
dominant, and the nondominant follicles atrophy. The predominant hormone
secreted from the ovary during the follicular phase is estrogen and induces
proliferation within the uterine lining. Approximately midcycle, there is a surge
in secretion of luteinizing hormone (LH) from the pituitary stimulating ovulation,
the release of an egg from the dominant follicle. In the absence of fertilization,
the ovum becomes the corpus luteum and secretes large amounts of progesterone.
Progesterone counteracts the estrogen effects on the endometrium, inhibiting its
proliferation and producing glandular changes to prepare the lining for
implantation of a fertilized ovum. Estrogen and progesterone exert a negative
feedback on FSH and LH secretion and these levels subsequently decrease. In the
absence of implantation, the corpus luteum involutes, progesterone and estrogen
levels fall, the endometrium sloughs away and menstruation ensues, starting the
cycle over again.
