Changes

The longest region of the oviduct, occupying more than half of its total length, and also has the largest diameter. This is the site of fertilisation. It is distinguished by its many '''mucosal folds'''. The ampulla is joined to the isthmus via the '''Ampullary-Isthmus junction'''. This junction is important in the mare, as it acts as a regulatory checkpoint allowing only fertilised ova to pass any further along the oviduct and into the uterus.

The longest region of the oviduct, occupying more than half of its total length, and also has the largest diameter. This is the site of fertilisation. It is distinguished by its many '''mucosal folds'''. The ampulla is joined to the isthmus via the '''Ampullary-Isthmus junction'''. This junction is important in the mare, as it acts as a regulatory checkpoint allowing only fertilised ova to pass any further along the oviduct and into the uterus.

=== Isthmus ===

=== Isthmus ===

The caudal end of the oviduct joined to the uterus. The Isthmus is thicker walled than the ampulla and smaller in diameter. Its folded mucosa  forms a functional reservoir for sperm in the female tract. Sperm in the female tract reach the isthmus of the oviduct and bind to the mucosal epithelial cells, forming a functional reservoir. The sperm are only released from the isthmus mucosa by the action of paracrine signals from an ova travelling down the oviduct.  The formation of a functional reservoir is a possible supporting mechanism of [[Fertilisation - Anatomy & Physiology|Block to polyspermy]], as only a few sperm are released from the isthmus mucosa at any one time. This results in only a few sperm being in the vicinity of the ova at a time and so in a position of fertilising the ova.

The caudal end of the oviduct joined to the uterus. The Isthmus is thicker walled than the ampulla and smaller in diameter. Its folded mucosa  forms a functional reservoir for sperm in the female tract. Sperm in the female tract reach the isthmus of the oviduct and bind to the mucosal epithelial cells, forming a functional reservoir. The sperm are only released from the isthmus mucosa by the action of paracrine signals from an ova travelling down the oviduct.  The formation of a functional reservoir is a possible supporting mechanism of [[Fertilisation - Anatomy & Physiology|block to polyspermy]], as only a few sperm are released from the isthmus mucosa at any one time. This results in only a few sperm being in the vicinity of the ova at a time and so in a position of fertilising the ova.

 

===Uterotubal Junction===

===Uterotubal Junction===

The oviducts open into the uterine horn through the uterine '''ostium'''.  This marks the site of the '''uterotubal junction'''. This junction is gradual in ruminants and pigs, but abrupt in the horse and carnivores. In the horse, the uterine ostium is located on top of a papilla, which forms a barrier against ascending infections.

The oviducts open into the uterine horn through the uterine '''ostium'''.  This marks the site of the '''uterotubal junction'''. This junction is gradual in ruminants and pigs, but abrupt in the horse and carnivores. In the horse, the uterine ostium is located on top of a papilla, which forms a barrier against ascending infections.