The Intricately Interactive Choreography of Conception

1. Male initiated: Up to 600 million sperm are deposited in the birth canal, of which only 200 reach the fertilization site in the uterine tube.  The Developing Human: Clinically Oriented Embryology, 10th ed., K. Moore et al., Elsevier (2016), pp. 25-26.

2. Male initiated: An enzyme produced by the prostate helps liquify the semen to facilitate its flow into the female reproductive tract.  Moore, p. 25.

3. Male initiated: Fructose produced by the seminal glands is a source of energy which powers the sperm’s movement through the female reproductive tract.  Moore, p. 25.

4. Male initiated: Sperm are nonmotile during storage in the epididymis of the testis, but they become motile when combined with seminal fluid.  They move slowly in the acidic environment of the vagina but move rapidly in the alkaline environment of the uterus.  Moore, p. 26.

5. Female initiated: When ovulation occurs, the cervical mucus content increases in volume and becomes less viscid (less thick and sticky), making it a more favorable medium for sperm transport.  Moore, p. 25.

6. Female initiated: Some sperm are stored in the folds of the cervical crypts and are gradually released into the fallopian tubes.  This maternal metering mechanism increases the chances of fertilization.  Moore, p. 27.

7. Female initiated: Cervical mucus helps capture and nourish sperm on their way to meet the egg in the uterine tube.  ClevelandClinic.org.

8. Female initiated: Sperm are usually capacitated (activated) while they are in the uterus or fallopian tubes by substances secreted by parts of the female genital tract.  Moore, p. 26.

9. Female initiated: Female reproductive fluid (FRF) interacts with sperm, increasing their motility and longevity and ultimately achieving fertilization success.  “Sperm Accumulation Induced by the Female Reproductive Fluid ….” PubMed, Sept. 18, 2021.

10. Female initiated: Chemical signals (attractants) secreted by the female’s oocyte (egg) guide sperm to the oocyte.  Moore, p. 27.

11. Male initiated: Carbohydrate binding molecules and gamete-specific proteins on the surface of the sperm are involved in egg-sperm recognition and union.  Moore, p. 28.

12. Female initiated: Sperm cannot fertilize the egg until a glycoprotein coat and seminal proteins are removed from the acrosome, or head of the sperm, by substances secreted by the female genital tract.  Moore, p. 26.

13. Female initiated: When capacitated sperm come into contact with the corona radiata (membrane) surrounding a secondary oocyte, they undergo complex molecular changes which facilitate fertilization.  Moore, p. 26.

14. Male initiated: Although apertures in the membrane surrounding the oocyte appear to be created mainly from the action of an enzyme released from the acrosome (head) of the sperm, maternal mucosal enzymes also appear to assist in creating these openings.  Moore, p. 29.

15. Male initiated: Fertilization is a complex sequence of coordinated molecular events that begins with contact between a sperm and an oocyte and ends with the intermingling of maternal and paternal chromosomes.  Moore, p. 28.

16. Male initiated: The human oocyte contains some 8,000 zinc compartments, each storing approximately 1 million zinc atoms.  When an egg makes contact with a sperm cell, these zinc atoms burst out of the egg.  The zinc which now surrounds the egg strengthens its membrane against penetration by additional sperm.  “Scientists Just Captured the Flash of Light that Sparks when a Sperm Meets an Egg,” April 27, 2016, ScienceAlert.com.

17. Male initiated: The pronuclei of the sperm and oocyte merge, each combining its 23 chromosomes with the 23 chromosomes of the other, forming the 46-chromosome embryo, which at this single-cell stage is called a zygote.  Moore, p. 29.