1054 Gonadotropin Secretion Overian Events Thickness Of Endometrium Ovarian Hormone Secretion Days Part Six Reproductio 1 (63.48 KiB) Viewed 51 times
1054 Gonadotropin Secretion Overian Events Thickness Of Endometrium Ovarian Hormone Secretion Days Part Six Reproductio 2 (63.48 KiB) Viewed 51 times
1054 Gonadotropin secretion. Overian events Thickness of endometrium Ovarian hormone secretion Days PART SIX Reproduction and the Life Cycle (a) Ovarian cycle Days FSH Developing follicles Primary (b) Menstrual cycle Menstrual fluid Secondary Menstrual phase Estradiol body: late yellow Tertiary Follicular phase Proliferative phase When the follicle ruptures, it collapses and bleeds into the antrum. As the clotted blood is slowly absorbed, granulosa and theca interna cells multiply and fill the antrum, and a dense bed of blood capillaries grows amid them. The ovulated follicle has now become a structure called the corpus luteum," named for a yellow lipid that accumulates in the theca interna cells. These cells are now called lutein cells. The transformation from ruptured fol- licle to corpus luteum is regulated by LH; hence, LH is also called luteotropic hormone. Ovulation Corpus luteum Involution Progesterone Luteal phase 23 19 21 Secretory phase 25 23 25 Corpus albicans New primordial follicles GURE 28.13 The Female Sexual Cycle. (a) The ovarian cycle (events in the ovary). (b) The menstrual cycle (events in the uterus). The o hormone levels in part (a) are drawn to the same scale, but those in part (0) are not. The peak progesterone concentration is about times as high as the peak estradiol concentration. APR 27 Premenstrual phase LH stimulates the corpus luteum to continue growing and to secrete rising levels of estradiol and progesterone There is a 10-fold increase in progesterone level (fig. 28.14) which has a crucial role in preparing the uterus for the possi bility of pregnancy. Notwithstanding its luteinizing role, bow ever. LH secretion declines steadily over the rest of the cycle. as does FSH. This is because the high levels of estradiol and progesterone, along with inhibin from the corpus luteum have a negative feedback effect on the pituitary. (This is the basis for hormonal birth control; see Deeper Insight 28.53 If pregnancy doesn't occur, the corpus luteum begins a process of involution, or shrinkage beginning around
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