Ovulation

In the days immediately preceding ovulation, under the influence of FSH and LH, the secondary follicle grows rapidly to a diameter of 25 mm. Coincident with final development of the secondary follicle, there is an abrupt increase in LH that causes the primary oocyte to complete meiosis I and the follicle to enter the preovulatory stage. Meiosis II is also initiated, but the oocyte is arrested in metaphase approximately 3 hours before ovulation. In the meantime, the surface of the ovary begins to bulge locally, and at the apex, an avascular spot, the stigma, appears. The high concentration of LH increases collagenase activity, resulting in digestion of collagen fibers surrounding the follicle. Prostaglandin levels also increase in response to the LH surge and cause local muscular contractions in the ovarian wall. Those contractions extrude the oocyte, which together with its surrounding granulosa cells from the region of the cumulus

Antrum

Granulosa cells

Luteal cells

Antrum

Oocyte Theca Luteal Cells

Oocyte i 2nd meio division

A Preovulatory follicle

Theca intern

Oocyte i 2nd meio division

1st polar body

Theca intern

1st polar body

Theca Externa

Ovarian strom

Theca externa

B Ovulation

Cumulus oophorus Fibrin cells

Ovarian strom

Theca externa

Blood vessels

Luteal cells

Blood vessels

C Corpus luteum

A Preovulatory follicle

B Ovulation

C Corpus luteum

Figure 2.2 A. Preovulatory follicle bulging at the ovarian surface. B. Ovulation. The oocyte, in metaphase of meiosis II, is discharged from the ovary together with a large number of cumulus oophorus cells. Follicular cells remaining inside the collapsed follicle differentiate into lutean cells. C. Corpus luteum. Note the large size of the corpus luteum, caused by hypertrophy and accumulation of lipid in granulosa and theca interna cells. The remaining cavity of the follicle is filled with fibrin.

oophorus, breaks free (ovulation) and floats out of the ovary (Figs. 2.2 and 2.3). Some of the cumulus oophorus cells then rearrange themselves around the zona pellucida to form the corona radiata (Figs. 2.4-2.6).

CLINICAL CORRELATES Ovulation

During ovulation, some women feel a slight pain, known as middle pain because it normally occurs near the middle of the menstrual cycle. Ovulation is also generally accompanied by a rise in basal temperature, which can be monitored to aid in determining when release of the oocyte occurs. Some women fail to ovulate because of a low concentration of gonadotropins. In these cases, administration of an agent to stimulate gonadotropin release and hence ovulation can be employed. Although such drugs are effective, they often produce multiple ovulations, so that the risk of multiple pregnancies is 10 times higher in these women than in the general population.

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Responses

  • alyce
    Can women feel ovocyte release during ovulation?
    8 years ago

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