D. A surge of FSH causes ovulation – Explanation
| LH surge causes ovulation |
Menstrual cycle
The menstrual cycle may be divided into the following phases:
| Days | |
| Menstruation | 1-4 |
| Follicular phase (proliferative phase) | 5-13 |
| Ovulation | 14 |
| Luteal phase (secretory phase) | 15-28 |
Further details are given in the table below
| Follicular phase (proliferative phase) | Luteal phase (secretory phase) | |
| Ovarian histology | A number of follicles develop. One follicle will become dominant around the midfollicular phase. | Corpus luteum |
| Endometrial histology | Proliferation of endometrium. | Endometrium changes to secretory lining under influence of progesterone. |
| Hormones | A rise in FSH results in the development of follicles which in turn secrete oestradiol. When the egg has matured, it secretes enough oestradiol to trigger the acute release of LH. This in turn leads to ovulation. | Progesterone secreted by corpus luteum rises through the luteal phase. If fertilisation does not occur the corpus luteum will degenerate and progesterone levels fall Oestradiol levels also rise again during the luteal phase |
| Cervical mucus | Following menstruation the mucus is thick and forms a plug across the external os Just prior to ovulation the mucus becomes clear, acellular, low viscosity. It also becomes ‘stretchy’ – a quality termed spinnbarkeit |
Under the influence of progesterone it becomes thick, scant, and tacky |
| Basal body temperature |
Falls prior to ovulation due to the influence of oestradiol |
Rises following ovulation in response to higher progesterone levels |
