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RepRoductive ` REPRODUCTIVE—PHySIOlOgy RepRoductive ` REPRODUCTIVE—PHySIOlOgy SectioN iii 631
Oogenesis 1° oocytes begin meiosis I during fetal life and complete meiosis I just prior to ovulation.
Meiosis I is arrested in prOphase I for years until Ovulation (1° oocytes).
Meiosis II is arrested in metaphase II until fertilization (2° oocytes). “An egg met a sperm.”
If fertilization does not occur within 1 day, the 2° oocyte degenerates.
Oogonium 1° oocyte 2° oocyte Ovum
Diploid Diploid Haploid Haploid
(2N, 2C) (2N, 4C) (1N, 2C) (1N, 1C)
Arrested in Arrested in
prophase I metaphase II
until ovulation until fertilization
23
single
chromatids
23
sister Ovum
chromatids
46 46 Polar body
single sister
chromosomes chromatids
Polar body
N = ploidy
C = # of chromatids Polar body
(can degenerate
or give rise to 2
polar bodies) Polar body
Replication Meiosis I Meiosis II
(interphase)
Ovulation estrogen, GnRH receptors on anterior Mittelschmerz—transient mid-cycle ovulatory
pituitary. Estrogen surge then stimulates LH pain (“Middle hurts”); classically associated
release ovulation (rupture of follicle). with peritoneal irritation (eg, follicular
temperature (progesterone induced). swelling/rupture, fallopian tube contraction).
Can mimic appendicitis.
FAS1_2019_15-Repro.indd 631 11/7/19 5:52 PM
