Understanding the Avian Digestive System

Aug 27, 2024

Notes on Avian Gastrointestinal Tract

Overview of Avian Digestive System

  • Unique compared to mammals
  • Shorter intestinal tract

Structure and Function of Mouth

  • Beak: Lightweight, used to swallow food whole
  • Tongue:
    • Collects, moves, swallows food
    • Covered with lateral barbs
    • Moves food to the back of the mouth
  • Salivary Glands: Less developed but help lubricate food
  • Taste Buds: Up to 300, located in the upper beak and anterior tongue
  • Laryngeal Mound: Assists in moving food into the esophagus

Esophagus

  • Function: Transports food from mouth to stomach
  • Thin-walled, expansive tube
  • Structure:
    • Four layers: mucosal, submucosal, muscular tunic, serosa
  • Sections:
    • Cervical (near beak)
    • Thoracic (near crop)
  • Glands: More numerous in the thoracic esophagus
  • Movement: Via myenteric plexus nerves, not muscle contractions

Crop

  • Structure: Thin-walled pouch at base of thoracic esophagus
  • Function: Holds food until released to the stomach
  • Storage Time: Up to 12 hours
  • Note: No digestion occurs here; softening of feed may happen
  • Condition: Sour crop (fermentation and bacterial infection)

Proventriculus (True Stomach)

  • Function: Actual digestion begins here
  • Structure:
    • Thick walls with five layers
    • Glandular tissue produces digestive secretions (HCl, pepsin, gastrin)
  • Processes: Softens food, prepares it for the gizzard

Gizzard (Ventriculus)

  • Function: Grinding of food
  • Structure: Round organ with two lobes
  • Surface: Lined with keratinized material (coilin) that withstands digestion
  • Muscle Action: Requires grit and small rocks for effective grinding

Small Intestine

  • Length: More than 4.5 feet
  • Sections:
    • Duodenum: Pancreas lies here; digestive enzymes released
    • Jejunum and Ileum: Majority of nutrient absorption occurs
  • Hormones: Released to aid digestion (trypsin, chymotrypsin, amylase, lipase)
  • Nutrient Absorption: Villi increase surface area for glucose, calcium, vitamin B12

Large Intestine

  • Length: 4 inches
  • Function: Water reabsorption, storage of undigested waste
  • Structure: Ends at cloaca; referred to as colon
  • Sica: Blind pouches for water reabsorption and fermentation
  • Nutrient Production: Bacteria produce fatty acids and B vitamins but minimal absorption occurs

Cloaca

  • Junction of digestive and urinary tracts
  • In hens, reproductive tract enters here
  • Waste mixed and excreted through the vent
  • Functionality: Flexible to pass eggs from reproductive system

Conclusion

  • The avian digestive system is optimized for efficient processing of food, from swallowing to absorption and waste excretion.