Ch. 12 - Spermatozoa in the Female Tract
Following insemination, viable spermatozoa that are retained in the female reproductive tract must:
Undergo capacitation
Bind to the oocyte
Be transported through the uterus to the oviduct
Undergo the acrosome reaction
Transverse the cervix
Penetrate the zona pellucida and fuse with the oocyte plasma membrane
After fusion with the plasma membrane, the fertilizing spermatozoon enters the oocyte cytoplasm and its nucleus decondenses; the male pronucleus is formed and this signifies successful fertiization
Spermatozoa are lost from the femal tract by:
Phagocytosis by neutrophils
Retrograde transport
Spermatozoal transport consists of two phases:
Rapid Phase: primarily the result of elevated tone and motility of the muscularis of the female tract
Sustained Phase: spermatozoa are transported to the oviducts in a "trickle-like" effect from so-called reservoirs in the cervix and the uterotubal junction
During estrus the cervix produces mucus, which in the cow consists of two types:
Sialomucin: a mucus of low viscosity that creates "priveledged pathways" by which the sperm can travel through
Sulfomucin: produced in the apical portions of the cervical epithelium covering the tips of the cervical folds; this type is quite viscous
Postcapacitation sequence of events leading to fertilization:
4 - Penetration of the zona pellucida
5 - Sperm-oocyte membrane fusion
3 - Acrosomal reaction
6 - Sperm engulfed
2 - Binding to the zona pelucida
7 - Decondensation of sperm nucleus
1 - Hyperactive motility
8 - Formation of male pronucleus
The sperm plasma membrane contains two zona binding sites:
Primary Zona Binding Region: responsible for adherence of spermatozoa to the zona pellucida
Acrosome Reaction Promoting Ligand: signal transduction occurs to initiate the acrosomal reaction
Purpose of the acrosomal reaction:
Enables spermatooa to penetrate the zona pellucida
Modifies the equatorial segment so that it can later fuse with the plasma membrane of the oocyte