Avian Digestive System

• Parts of the avian digestive system

  • Oropharynx
  • Esophagus
  • Stomach
  • Duodenum
  • Jejunum
  • Ileum
  • Ceca
  • Colon
  • Cloaca
  • Vent
  • Choana
  • Crop
  • Proventriculus
  • Gizzard
  • Coprodeum, urodeum and proctodeum

  
• Objectives


  • Know the structures and function of each part of avian digestive tract
  • Identify and recognize the components of avian digestive tract
  • Describe the structures of each component of avian digestive tract

  
• Types of avian ceca

  • Purple heron (Ardea purpurea)
  • Sparrow-hawk (Accipiter nisus)
  • Marabou (Leptotilos crumeniferus)
  • Rail (Rallidae)
  • Helmet guineafowl (Numidia melagris)
  • Barn owl (Tyto alba)
  • Northern screamer (Chauna chavaria)
  • Great bustard (Otis tarda)
  • Ostrich (Struthio camelus)
• Oropharynx


  Combine cavity that extends from the mouth to the esophagus
• Oropharynx


  • Roof - hard palate
  • Floor - mandible, tongue, and laryngeal mound
  • Lips and teeth are absent
  • Palate present a choana that connects with nasal cavity
• Esophagus


  • Proximal end lies between trachea and cervical muscles, then deviates to the right
  • Esophagus and trachea are movable
  • At thoracic inlet, its ventral wall expand to form crop (R) and lies against the breast muscles
  • Capable of great distension. Its propria contains mucous glands whose secretion lubricates the passage of bolus
• Crop


  • Most birds but not all have a crop (geese, owls). In some (ducks), it forms a fusiform enlargement of the esophagus
  • Crop stores food for short periods when the muscular stomach is full

  
• Crop secretion


  A secretion from the lining of the crop of parent birds that is regurgitated to young birds. It is found among all pigeons and doves where it is referred to as pigeon milk.

  
• Stomach


  Divided into glandular (proventriculus) and muscular (gizzard) parts
• Proventriculus


  • Ventrally contact with lobe of liver
  • Spindle-shaped
  • Its whitish mucosa is lined with a mucus secreting, columnar epithelium
  • Has numerous papillae. These produce HCl and pepsin
• Gizzard


  • Touches liver, contact with sternum and lower part of left lateral abdominal wall
  • Lens-shaped with convex surfaces facing more or less to the right and left
  • Has cranial and caudal blind sacs
  • Cranial blind sac connects with proventriculus
  • Consists of two thick muscles insert on glistening tendinous centers, one on each surface
  • Two thinner muscles cover the blind sacs
  • Mucous membrane is thin but very tough
  • This is why chickens do not need teeth. It is a muscular part of stomach and uses grit (small, hard particles of pebbles or sand) to grind grains and fibers into smaller, more digestible, particles. Powerful contractions of the gizzard crush the food

  
• Small intestine


  • Occupies caudal part of body cavity, contact with gizzard and reproductive organs
  • Consists of duodenum, jejunum, ileum, and a short colon
  • Two ceca arise from the ileocolic junction
  • Passes caudally from right surface of gizzard
  • Formed a tight U-shaped loop. Most of the loop lies on the abdominal floor
  • Pancreas lies between the limbs and empties into distal end of duodenum
  • Bile ducts enter close by
  • Forms loose coils along the edge of mesentery
  • Thin-walled, its content appear greenish
  • Patches of aggregate lymph nodules present

  
• Ileum


  • Continues from the jejunum without demarcation
  • A small scar tissue remnant of the yolk sac (after 10 days of age)
  • Located on the antimesenteric side of the intestine, contains lymphoid tissue and is part of the GALT
  • It is located at the junction between the jejunum and the ileum
• Ceca and colon


  • Ceca - long in chicken and turkey
  • Arise at ileocolic junction
  • They pass cranially at first, then double back so that their blind ends usually lie near cloaca
  • Proximal segment has a heavy muscle coat (cecal sphincter) and contains much lymphoid tissue (ceca tonsil)
  • Bacterial breakdown of cellulose occurs in ceca
  • Colon - ends by slight enlargement at cloaca (about 10 cm long)
  • Common to digestive & urogenital systems
  • Opens at vent
  • Colon, ureters, and deferent ducts (or left oviduct) enter it at various levels
  • Divided into coprodeum, urodeum, and proctodeum by two, more or less complete annular folds
  • Coprodeum -continuation of colon in which feces are stored
  • Urodeum and proctodeum - associated with urogenital system