When does the secondary oocyte complete the second meiotic division?
Just after fertilization
The secondary oocyte completes meiosis II only just after fertilization. Female meiosis is arrested twice. The primary oocyte is held in prophase I (dictyate or diplotene stage) from about the fifth month of fetal life until puberty. The LH surge completes meiosis I roughly 36 hours before ovulation, producing the secondary oocyte and the first polar body in an unequal division. The secondary oocyte immediately enters meiosis II and arrests again in metaphase II, and is ovulated in that state. Sperm penetration triggers a calcium wave that inactivates cytostatic factor and maturation-promoting factor, releasing the block, so meiosis II finishes with extrusion of the second polar body.
Why the others are wrong: Just before ovulation is when the first meiotic division completes under the LH surge. Just after ovulation is wrong because leaving the follicle does not release the metaphase II arrest. Just before fertilization is wrong because sperm entry itself is the trigger; unfertilised, the oocyte degenerates within 12 to 24 hours still in metaphase II.
Key point: Meiosis I completes just before ovulation (first polar body); meiosis II completes only after sperm penetration (second polar body).
Similar Questions
Consider the following statements with respect to endometrial cycle:
1. The basal zone is uninfluenced by any hormone.
2. Saw-toothed glandular epithelium is seen in secretory phase.
3. Stratum compactum contains mainly the glands and less stroma.
4. Pseudostratification is seen in proliferative phase of menstrual cycle.
Which of the statements given above are correct?
The growth and differentiation of primordial follicles is under the control of which hormone?
Which one of the following statements explains self-priming of gonadotrophs?
Important Questions from Physiology of Menstruation & Fertilization
- Implantation of a fertilised ovum occurs on which day following fertilisation?
- Withdrawal bleeding following administration of progesterone in a case of secondary amenorrhea indicates all EXCEPT:
- Diagnostic criteria for PCOD are:
1. Oligo/amenorrohoea
2. Hyperandrogenism
3. Polycystic ovaries on ultrasound
Which of the above are correct? An 18 year old unmarried girl comes with complaints of heavy, prolonged bleeding during menses. Which among the following investigations is NOT usually advised?
- Which one of the following is true about Basal body temperature?
1. Biphasic pattern
2. Increase in the level of progesterone and norepinephrine
3. Temperature falls by $0.5^{\circ}C$ after ovulation
4. It can predict ovulation precisely
Select the correct answer using the code given below:
