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FERTILIZATION
Joyce LearyJoyce LearySeptember 5, 2001September 5, 2001
THE SPERM:
must reach and penetrate the ovum.
must activate the ovum to resume nuclear and cytoplasmic division necessary for embryonic development.
contributes the paternal complement of chromosomes to the new embryo.
determines the sex of the embryo.
SPERM MATURATIONFrom stationary round cell (spermatogonia) to motile, tadpole-like cell (spermatid):Meiosis: 1 diploid cell 4 haploid gametesCentriole flagellumGolgi apparatus acrosomal vesicleMitochrondria collect at junction of flagellum
and head (at midpiece)Head shape streamlines, cytoplasm is stripped
off, and nucleus condenses
Spermiogenesis
From Wheater’s Functional Histology, 4th edition, 2000.
SPERM MATURATIONAcrosomal vesicle - contains enzymes that digest proteins and complex sugars. Important for egg recognition Lyses outer covering of egg
Flagellum – whip-like structure that propels the sperm using ATPATP is produced by the mitochrondriaThe enzyme dynein hydrolyzes ATP to release
energy Dynein is attached to the microtubules of the
flagellum
The Sperm Head
Head: EM, LS × 14 000AC = acrosome; PM = plasma membraneFrom Wheater’s Functional Histology, 4th ed., 2000.
The head of a mature sperm, lengthwise, is approximately 1/20 the diameter of a mature ovum.
The Sperm Neck
Neck (middle piece and principal piece): EM, LS × 17 000Mi = mitrochondria; C = cytoplasm; F, Rn, Rb, & An = all parts of flagellum structureFrom Wheater’s Functional Histology, 4th ed., 2000.
OvulationAt ovulation, the secondary oocyte is released:The secondary oocyte is frozen at metaphase of
the 2nd meiotic division
Accompanying the secondary oocyte:Corona radiata (same as cumulus oophorus) –
follicular cells that accompanied the ovum during ovulation
Zona pellucida – right next to ovum; extracellular matrix proteins that form a barrier assuring species-specific fertilization only
Ovum with corona radiata (arrow): (in vitro)
Advanced Fertility Center of ChicagoAdvanced Fertility Center of Chicagohttp://www.advancedfertility.com/http://www.advancedfertility.com/
THE OVUMUnlike the sperm, the ovum is accumulating nutrients and material throughout maturation, not eliminating it.The ovum must provide food reserves until the
embryo is able to feed on exogenous materials from the mother.
The ovum contributes the maternal complement of chromosomes to the new embryo.The ovum must reject all sperms but one.
The OvumGraafian follicleAzan × 75
FA = follicular antrum
CR = corona radiata
O2 = secondary oocyte
ZG = zona granulosa
TI = theca interna
The oocyte is released along with the corona radiata.
Notice the clear ring just around the ovum (arrow tip): this is the zona pellucida.
From Wheater’s Functional Histology, 4th ed., 2000.
Fertilization:
Location: usually the ampulla of the oviduct (fallopian tube/uterine tube) Fertilization can take place in any part of the tube, and even
in the abdominal cavity, but not in the uterus.
From Wheater’s Functional Histology, 4th ed., 2000.
Getting to the right site:Sperm: During ejaculation, the sperms are propelled
from the urethra by peristaltic contractions of the vas deferens musculature.
Sperm use their flagellum to move through the cervical canal.
The enzyme vesiculase (from seminal vesicles) coagulates some of the semen to prevent backflow into the vagina.
Fructose (from seminal vesicles) is an energy source for the sperm.
Getting to the right site:Helping the sperm: At ovulation, the cervical mucus increases in amount
and becomes less thick, allowing easier sperm transport. Passage of the sperm through the uterus and oviduct
occurs mainly due to muscular contractions of these organs.
Oocyte: The ends of the oviducts come into close contact with
the ovary during ovulation. Fimbriae of oviduct ends “sweep” the ovulated ovum into
the oviduct. Peristaltic waves of oviduct musculature bring the ovum
into the ampulla of the oviduct.