Fertilization

Definition

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

  1. An ovum is capable of fertilization for 24 to 48 hours. After this time, the ovum atrophies and becomes nonfunctional.
  2. The functional life of a spermatozoon is about 48-72 hours.
  3. The normal amount of semen in an ejaculation is about 3-5 cc (average: 2.5 ml).
  4. The number of sperms in an ejaculate is 50-200 million per milliliter or an average of 400 million sperm per ejaculation.
  5. Spermatozoon reaches the cervix within 80 seconds and the outer end of the fallopian tube within 5 minutes.

Sequential Events of Fertilization

  1. 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.
  2. 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.
  3. The ovum is propelled along the length of the tube through the peristaltic action of the fallopian tube and the movements of cilia.
  4. It is easier for spermatozoon to penetrate the vagina as the viscosity of cervical mucus is decreased.
  5. 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.
  6. Capacitation, a process where sperm-binding receptor sites are revealed, takes place right before fertilization.
  7. 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.
  8. Right after penetration, the chromosomal material of the ovum and sperm combine. The resulting structure is termed zygote (fertilized ovum).
  9. 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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Daisy Jane Antipuesto RN MN

Currently a Nursing Local Board Examination Reviewer. Subjects handled are Pediatric, Obstetric and Psychiatric Nursing. Previous work experiences include: Clinical instructor/lecturer, clinical coordinator (Level II), caregiver instructor/lecturer, NC2 examination reviewer and staff/clinic nurse. Areas of specialization: Emergency room, Orthopedic Ward and Delivery Room. Also an IELTS passer.

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