Thursday, February, 09, 2012

Menstrual Disorders - Introduction

Table of Contents

  • Gonadotropin-releasing hormone (GnRH) is released by the hypothalamus.
  • GnRH stimulates the pituitary gland to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
  • Estrogen, progesterone, and the male hormone testosterone are secreted by the ovaries at the command of FSH and LH.
Pituitary hormones Click the icon to see an image of the pituitary gland.

Ovulation

Ovulation is the process where a mature egg (ovum) is released from the ovary. The egg begins its development inside a follicle of the ovary:

  • With the start of each menstrual cycle, follicle-stimulating hormone (FSH) prompts several follicles to mature over a two-week period until their eggs nearly triple in size. Only one follicle becomes dominant, however, during a cycle.
  • FSH signals this dominant follicle to produce estrogen, which enters the bloodstream and reaches the uterus. There, estrogen stimulates the cells in the uterine lining to reproduce, therefore thickening the walls.
  • Estrogen levels reach their peak around the 14th day of the cycle (counting days beginning with the first day of a period). At that time, they trigger a surge of luteinizing hormone (LH).

LH serves two important roles:

  • First, the LH surge around the 14th cycle day stimulates ovulation. It does this by causing the dominant follicle to burst and release its egg into one of the two fallopian tubes. Once in the fallopian tube, the egg is in place for fertilization.
  • Next, LH causes the ruptured follicle to develop into the corpus luteum, a yellow mass of cells. The corpus luteum provides a source of estrogen and progesterone during pregnancy.

Fertilization

Review Date: 07/26/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)