In the prepubertal state, the concentration of sex steroids and gonadotropins is low. The hypothalamic gonadostat is functional but highly sensitive to low levels of sex steroids,with the onset of puberty there is decreased sensitivity of the hypothalamus to negative feedback by sex steroids, increased release of LRF, and enhanced secretion of gonadotropins. In the negative feedback mechanism, the hypothalamus is less sensitive to feedback by sex steroids (adult set point) and adult levels of gonadotropins and sex steroids are present.
With rising estradiol production during the follicular phase of the cycle, the endometrial stroma thickens and the endometrial glands become elongated, this is a proliferative endometrium. The endometrium reaches a maximal thickness at the time of ovulation.
When ovulation occurs, the hormonal balance changes from an estrogenic state to a progestational state. P is not a mitogen, but causes differentiation of the tissues that contain p receptors. P converts the proliferative endometrium into a secretory endometrium. The endometrium stroma becomes loose and edematous, and blood vessels entering the endometrium become thickened and twisted. The endometrial glands, which were straight and tubular in the proliferative phase of the endometrium, become tortuous and contain secretory material within the lumina.
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