Physiology of the natural cycle

A. Hourvitz, E. Y. Adashi

Research output: Contribution to journalReview articlepeer-review

Abstract

Optimal ovarian estrogen biosynthesis is contingent on cooperation of two gonadotropins (LH and FSH) and two ovarian somatic cell types (granulosa and theca). In contrast, progesterone biosynthesis is primarily LH dependent and is carried out at the level of the granulosa-lutein cell. The pronounced progestational capabilities of the corpus luteum reflect its highly vascular nature, a phenomenon resulting from the breaching of the follicular basement membrane at the time of ovulation along with neovascularization of the former follicular apparatus. Follicle-stimulating hormone reception seems to constitute an early feature of the granulosa cell. Consequently, the FSH receptor provides the granulosa cell with a window to the outside world through which other signaling systems can be acquired. The indispensability of estrogens to intraovarian physiology is now being challenged. A strong body of evidence suggests that the primate/ human follicle may not depend on estrogen for its growth and maturation. The ovary may in fact have a zeitgeber role during the menstrual cycle, a time-keeping function subserved by the activities of the cyclic structures of the dominant ovary. The 28-day menstrual cycle is the result of the intrinsic life span of the cyclic ovarian dominant structure and not the result of time changes dictated by the brain or pituitary. The dominant follicle determines the length of the follicular phase, the corpus luteum determining the length of the luteal phase.

Original languageEnglish
Pages (from-to)1-16
Number of pages16
JournalInfertility and Reproductive Medicine Clinics of North America
Volume12
Issue number1
StatePublished - 2001
Externally publishedYes

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