Gynecology Kasr Al-Ainy Department PDF

## Gynecology Kasr Al-Ainy Depart... ### The Menstrual Cycle and Associates Disorders #### THE TWO-CELL, TWO-GONADOTROPHIN hypothesis of oestrogen production A) Within theca cells; LH stimulates conversion of cholesterol to androgens, which are then transported from theca cells to granulosa cells...

## Gynecology Kasr Al-Ainy Depart... ### The Menstrual Cycle and Associates Disorders #### THE TWO-CELL, TWO-GONADOTROPHIN hypothesis of oestrogen production A) Within theca cells; LH stimulates conversion of cholesterol to androgens, which are then transported from theca cells to granulosa cells B) Within granulosa cells; FSH stimulates aromatization of androgens into oestrogens by the enzyme aromatase. - Oestradiol (E2) the chief ovarian oestrogen; - Enhances the induction of FSH receptors on granulosa cells. - Acts synergistically with FSH to increase LH receptors in the granulosa cells. - Androgens produced within the theca cells; - At low levels enhance aromatization and hence increase oestrogen production. - At high levels inhibit aromatization and produce follicular atresia. #### CONTROL OF STEROIDOGENESIS: Apart from FSH, LH, oestrogen and androgens, some autocrine and paracrine mediators play an important role in the process of folliculogenesis as: A) Inhibin: A peptide produced by granulosa cells that attenuates FSH production and enhances LH-induced androgen synthesis, thus the dominant follicle can continue development and other follicles undergo atresia. B) Activin: A peptide produced by granulosa cells and the pituitary gland that augments FSH production, an action almost directly opposite to that of inhibin. C) Growth Factors: As Insulin like growth factor (IGF), fibroblast growth factor (FGF), and epidermal growth factor (EGF), may all help enhanced responsiveness to FSH. #### SELECTION OF THE DOMINANT FOLLICLE During folliculogenesis a dominant follicle is selected to continue growth, maturation, and ovulation. Other follicles will be arrested and later become atretic. - The selected follicle is characterized by having the highest number of FSH receptors in its granulosa cells, having the most efficient aromatase activity, the highest concentration of FSH-induced LH receptors, the greatest amounts of E2 and inhibin produced, and thus requiring the least FSH and LH levels to complete maturation. The provided image shows multiple diagrams: - **Figure 4-3**: Depicts the two-cell, two-gonadotrophin hypothesis of oestrogen production. - The image shows theca cells and granulosa cells, and the conversion of cholesterol to androgens, androgens to oestrogens. - **Figure 4-4**: A diagrammatic representation of the development of the primordial to mature follicle. - The image shows the different stages of follicle development, from the primordial follicle to the mature follicle, including the changes in size and structure. - It depicts the different cells and layers involved in follicle development, such as: - Basement lamina - Dictyate oocyte - Granulosa cells - Zona pellucida - Theca interna - Theca externa - Antrum - Blood vessel - Fully grown oocyte - The image labels the sizes of the follicles at each stage (40μm, 100μm, 200μm, and 400μm).