Avian Vent and Cloaca - Anatomy & Physiology

BACK TO THE AVIAN DIGESTIVE TRACT

Introduction

The hindgut of the avian digestive system terminates in the cloaca. The external opening through which faecal matter and uric acid is excreted is called the vent. The shape of the vent varies depending on species.

Avian Cloaca Diagram - Copyright RVC 2008

The Cloaca

• Colon, ureters and deferent ducts/left oviduct enter at various levels

• Divided into coprodeum, urodeum and proctodeum by complete annular folds

• Some urinary excretions arriving in the cloaca become incorporated with the ingesta and move in a retrograde fashion to the caeca, increasing the absorption of water and electrolytes from the urinary waste

• The coprodeum is the most cranial division of the cloaca
  • Continuation of the colon where faeces are stored
  • Bounded by the coprourodeal fold
  • Can be stretched by the faecal pressure so the central opening is everted through the vent

• The urodeum is the middle part of the cloaca
  • Caudal to the proctodeum fold
  • Uteric opening in dorsolateral wall above the papilla of the deferent duct/oviduct opening

Bursa of Fabricus - Copyright Nottingham 2008

• The proctodeum is the caudal segment
  • Short
  • Ends at the vent
  • Opening in the dorsal wall leads to the cloacal bursa

The Vent

• Horizontal slit

• Phallus of males on internal surface of the ventral lip

• During insemination the vent is inverted

Species Differences

• Galliformes (turkeys and chickens) can move urates from the urinary tract into the colon and caeca where ammonia is released for protein synthesis

• Small memebrane coveres the opening of the oviduct into the cloaca in ducks, geese and swans until sexual maturity