52. A couple has been trying to get pregnant for a few years. They finally decid
ID: 3519989 • Letter: 5
Question
52. A couple has been trying to get pregnant for a few years. They finally decide to consult with a specialist who informs them that the reason they are not able to have a baby is the low sperm count. The couple is a bit confused about this discovery because as far as they understand, it only takes a single sperm to fertilize an egg. How would you explain to this couple why low sperm count is the potential cause for their fertility problems? Use the following terms in your answe: secondary oocyte, uterus, uterine tube, zona pellucida (or corona radiata) and spermatozoa. (5)Explanation / Answer
Answer
Normally each ml of semen contains about 200 millions of spermatozoa. The minimum count of sperm required to get pregnancy is 2- 5 million. Sometimes less than 2 million are also given natural conceive but rare cases.
Even though 200 millions of spermatozoa enter into the vagina, only few thousand may reach the cervix of the uterus and 1% my reach the secondary oocyte and one sperm get succeed. Normally the fertilization occurs in the fallopian tubes or uterine tube. It occurs during ovulation within 12 – 24 hours. so the count of sperm plays an important role in getting pregnant.
The sequence of events in fertilization and getting pregnancy are
i. The entry of sperm into female genital tract
ii. Spermatozoa swim along the cervical canal, uterus and then enters into uterine tubes. The movement can be provided by antiperistaltic contractions by oxytocin from uterus and prostaglandins of spermatozoa.
iii. The spermatozoa enter the secondary oocyte through different layers like corona radiate of granulosa cells that surround the secondary oocyte and diffuse into Zona pellucid and inactive the entry of other sperm into the ovum. This penetration is enabled by CatSper protein.
The secondary oocyte divided into matured Ovum and second polar body. The polar body is expelled. The head of sperm becomes male pronucleus and nucleus of ovum becomes female pronucleus and finally leads to formation single diploid nucleus and developed into an embryo. In this way they get pregnant.
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