Oviduct - Anatomy & Physiology

Introduction

The Oviduct is the tube that links the ovary to the uterus and which the ovulated oocyte travels down to become fertilised by sperm present in the female tract. It is also refered to as the Fallopian tube, Uterine tube or Ovarian tube.

Structure

The oviduct is devided into 3 anatomical regions:

Infundibulum

• The cranial ovarian end of the oviduct.
• It comprises of numerous fimbrae and the opening into the oviduct tube, the ostium.

Ampulla

• 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

• 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 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 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 and carnivores, the uterine ostium is located on top of a papilla, which forms a barrier against ascending infections.

Function

• A connecting tube structure between the uterus and ovary where fertilisation occurs.
• To provide regulation check points for unfertilised oocytes.
• The mucosal glands produce oviduct secretions integral for:
  • Supporting the unfertilised oocyte
  • Supporting spermatozoa in the oviduct
  • Increasing the fertilising capabilities of the spermatozoa
  • Development of the early embryo

Anatomical Boundaries

• The Oviduct is suspended from the abdominal wall by the mesosalpnix broad ligament.

Histology

Infundibulum

Histological Section of the Oviduct to show Fimbriae of the Infundibulum- Courtesy of J.Bredl, Copyright RVC 2008

• Fimbriae
  • Finger like projections that aid the Infundibulum in gliding over the surface of the ovary. This action enhances the chances of the ovulated Oocyte being captured by the Infundibulum, as ovulation in domestic species does not occur in any one place. The exception to this being the mare, where ovulation always occurs from the ovulation fossa.

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Ampulla

Histological Cross-Section of the Oviduct to show the Ampulla- Courtesy of J.Bredl, Copyright RVC 2008

• Ciliated Columna Epithelium
• Thin muscularis layer
• Fern-like mucosal folds

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Isthmus

Histological Cross-Section of the Oviduct to show the Isthmus- Courtesy of J.Bredl, Copyright RVC 2008

• Simple columna Epithelium
• Thick muscularis layer divided into inner circular layer and outer longditudinal layer
• few mucosal folds

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Vasculature

• Tubal branch of the ovarian artery.