Sperm in the Female Tract - Anatomy & Physiology

Overview

There is immediate retrograde loss at the entrance to the cervix/uterus with phagocytosis by leukocytes.
In the cervix, sperm must travel through privileged pathways. This serves to eliminate non-motile sprem and remove some abnormalities.
In the Uterus, capacitation is initiated with some phagocytosis occuring.
In the Oviduct, capacitation is completed and sperm show hyperactive motility.
At the Uterotubal Junction, the acrosome reaction occurs and the spermatozoon penetrated the oocyte in fertilization with the formation of male and female pronuclei.

If semen is deposited in the cranial vagina, capacitation may begin as sperm ascend the cervix.
If semen is deposited in the caudal cervix (mare) or mid-cervix (sow) and immediately enters the uterus, capacitation is initiated in the uterus and completed in the isthmus of the oviduct.
During Capacitation, the plasma membrane of the sperm undergoes marked biochemical changes.
During mixing of sperm with seminal plasma, epididymal sperm become coated in seminal plasma proteins. These are stripped by the female tract environment. These proteins were the decapacitating agents that were rendering the sperm incapable of fertilization.
Once the plasma proteins have been stripped, the portions of molecules that can bind to the zona pellucida of the oocyte are exposed.
Membrane lipases and protein kinases destabilize the plasma membrane, enabling it to undergo fusion if it is brought close to another membrane (it is said to become 'fusogenic').
Normally, intracellular calcium levels are low. Entry of calcium ions causes a sharp rise in intracellular calcium that signals for the acrosome reaction to occur.
Sperm remain in the female tract awaiting fertilization by an ovulated oocyte, this can be:
- ~24 hours in a cow
- ~40 hours in a sheep
- ~7/8 days in a bitch
Sperm are a heterogenous population, so they are not all capacitated at the same rate.

Sperm must travel through the highly convoluted cervix.
During oestrus, the cervix produces mucus.
- Sialomucin: Low viscosity mucus produced by basal areas of cervical crypts.
- Sulfomucin: More viscous mucus produced in apical portions of the cervical epithelium covering the tips of cervical folds.
The difference in viscosity of the mucus creates two distinct environments within the cervix.
Sperm encountering sulfomucin are washed out of the tract.
Sperm encountering sialomucin swim into it, creating 'privileged pathways' in deeper cervical crypts. Sperm then traverse the cervix through these pathways.
Thus, the cervix acts as a filter to immotile sperm because in order to survive; the sperm must actively swim into the 'privileged pathways'.