Med’11 Embryology Fertilization
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| What is fertilization? | It is the fusion between sperm and ovum to form a zygote.
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| What is the normal site of fertilization? | In the laterla 1/3 of the Fallopian tube (the ampulla of the tube)
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| When can fertilization occur? Why? | Within 24 hours from ovulation.
The 2ry oocyte is viable for only 24 hours; by that time, it has just reached the lateral 1/3 of the Fallopian tube.
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| What are the steps of fertilization? | 1.Transport of Gametes 2.Sperm conditioning
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| How is the ovum transported to the site of fertilization? | In ovulation, fimbriated end of uterine tube becomes closely applied to ovary. Its fingerlike fimbria move back & forth over ovary & “sweep” 2ry oocyte into infundibulum of uterine tube. Oocyte then passes into ampulla of the tube by waves of peristalsis.
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| How is sperm transported to the site of fertilization? | 200-300 million sperms are deposited in fornix of vagina. Most sperms degenerate;300-500 reach fert. site.
Takes 2-7 hrs.
Cervical mucus inc and is less viscid.
Prostaglandins stimulate uterine motility, which help movement of sperm.
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| What characteristics or changes help the sperm reach the ovum? | At time of ovulation cervical mucus inc&becomes less viscid Prostaglandins in semen stimulate uterine motility at time of intercourse&assist in movement of sperm through uterus&uterine tubes to site of fert. in ampulla
Fructose in semen is energy source
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| What are the 2 changes of sperm conditioning? When must these changes occur? | Changes: 1.Capacitation 2.Acrosome reaction
Before fertilizing the ovum
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| How long does capacitation take? | 5-7 hours
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| Where does capacitation occur? | In uterus and uterine tubes
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| What happens during capacitation? | Glycoprotein coat and seminal plasma proteins are removed from cell membrane covering acrosomal capsule.
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| NOTE | *Sperm can’t fertilize oocyte when they are newly ejaculated.
*Capacitated sperms are more active.
*The acrosomal reaction can’t occur until capacitation has occurred.
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| Where does the acrosome reaction occur? | In the vicinity of the oocyte
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| What happens in the acrosome reaction? | It is under the influence of the substance produced by the corona radiata. Fusion occurs between the outer acrosomal membrane and the cell membrane of the corona radiata with the release of acrosomal enzyme.
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| What are the chemicals responsible for acrosome reaction? | a)Hyaluronidase results in digestion of the corona radiata.
b)Trypsin-like substance & zona lysin lead to penetration of the zona pellucida.
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