Female Hormonal System
The female hormonal system, like that of the male, consists of three hierarchies of hormones, as follows:
1. A hypothalamic releasing hormone, gonadotropin-releasing hormone(GnRH)
2. The anterior pituitary sex hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both of which are secreted in response to the release of GnRH from the hypothalamus
3. The ovarian hormones, estrogen and progesterone, which are secreted by the ovaries in response to the two female sex hormones from the anterior pituitary gland
These various hormones are not secreted in constant amounts throughout the female monthly sexual cycle; they are secreted at drastically differing rates during different parts of the cycle. Figure 81–3 shows the approximate changing concentrations of the anterior pituitary gonadotropic hormones FSH and LH (bottom two curves) and of the ovarian hormones estradiol (estro-gen) and progesterone (top two curves).
The amount of GnRH released from the hypothal-amus increases and decreases much less drastically during the monthly sexual cycle. It is secreted in short pulses averaging once every 90 minutes, as occurs in the male.
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