Fertilization is the union of an ovum and a spermatozoon. It is also called conception, impregnation or fecundation and usually occurs in the outer third of the fallopian tube, the ampullar portion.
Important facts about fertilization
- An ovum is capable of fertilization for 24 to 48 hours. After this time, the ovum atrophies and becomes nonfunctional.
- The functional life of a spermatozoon is about 48-72 hours.
- The normal amount of semen in an ejaculation is about 3-5 cc (average: 2.5 ml).
- The number of sperms in an ejaculate is 50-200 million per milliliter or an average of 400 million sperm per ejaculation.
- Spermatozoon reaches the cervix within 80 seconds and the outer end of the fallopian tube within 5 minutes.
Sequential Events of Fertilization
- An ovum is surrounded by a ring of polysaccharide called the zona pellucida and a circle of cells called corona radiate as it is forced out of the graafian follicle of the ovary during ovulation. These surrounding cells serve as a protective buffer of the ovum against injury.
- The fimbrae, fine, hair-like structures that line the openings of the fallopian tubes initiate currents that propel the ovum and surrounding cells into the nearby fallopian tube.
- The ovum is propelled along the length of the tube through the peristaltic action of the fallopian tube and the movements of cilia.
- It is easier for spermatozoon to penetrate the vagina as the viscosity of cervical mucus is decreased.
- Spermatozoon moves through the cervix and the body of the uterus and into the fallopian tubes to the ovum by means of their tails (flagella) and uterine contractions.
- Capacitation, a process where sperm-binding receptor sites are revealed, takes place right before fertilization.
- As the sperms move toward the ovum and cluster around the ovum’s protective layer of cells HYALURONIDASE is released and dissolves the layer of cells that protects the ovum.
- Right after penetration, the chromosomal material of the ovum and sperm combine. The resulting structure is termed zygote (fertilized ovum).
- The ovum always contains the X-chromosome. A sperm contains either an x or Y chromosome. If an X-carrying sperm fertilizes an ovum the resulting structure will have two X chromosomes and the child will be female (XX). If a Y-carrying chromosome fuses with an ovum, the resulting structure will have an X and Y chromosome and the child will be male (XY).
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