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FERTILIZATION Joyce Leary September 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 MATURATION From stationary round cell (spermatogonia) to motile, tadpole-like cell (spermatid): Meiosis: 1 diploid cell  4 haploid gametes Centriole  flagellum Golgi apparatus  acrosomal vesicle Mitochrondria  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, 4 th edition, 2000.

SPERM MATURATION Acrosomal 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 ATP ATP is produced by the mitochrondria The enzyme dynein hydrolyzes ATP to release energy Dynein is attached to the microtubules of the flagellum

The Sperm Head Head: EM, LS × AC = acrosome; PM = plasma membrane From Wheater’s Functional Histology, 4 th ed., 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 × Mi = mitrochondria; C = cytoplasm; F, Rn, Rb, & An = all parts of flagellum structure From Wheater’s Functional Histology, 4 th ed., 2000.

Ovulation At ovulation, the secondary oocyte is released: The secondary oocyte is frozen at metaphase of the 2 nd 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 Chicago

THE OVUM Unlike 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 Ovum Graafian follicle Azan × 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, 4 th 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, 4 th 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.