Digestive System


    The wood duck is representative of most members of the Class Aves.  They have a unique digestive system adapted to their diet that consists mostly of seeds, acorns, berries, and grains.  The wood duck has a beak with serrated edges that help with the breaking down of food.  Their mouth consists of a tongue that moves food through the oral cavity into the pharynx and forms a bolus.  The pharynx is a passage way for air and food to the esophagus.  The esophagus in birds is specialized with a keratin layer that protects it from seeds and grains.  The widened portion of the esophagus found only in grainiverous birds is the crop.  The crop is a temporary storage for food  where mechanical breakdown occurs before food is either regurgitated or moved down the esophagus.  The proventriculus is a thin walled glandular section of stomach that secretes digestive enzymes(Kardong, 2002).  The ventriculus (gizzard) is a  thick muscled structure that contains hard grit and pebbles that mechanically breaks down large food.  Now, food passes to the small intestine where chemical breakdown of food occurs and the nutrients are absorbed.  There are specialized organs that lead into the small intestine and help break down food products.  The liver is a large organ that secretes bile to the small intestine and emulsifies fats.  The pancreas is a second specialized organ that secretes digestive enzymes.  Before entering the large intestine food moves into the ceca which digest plant cellulose using the enzyme cellulase.  Now that the nutrients in the food have been absorbed, the undigested food products pass into the large intestine where water is reabsorbed and compacted waste passes.  The undigested waste, along with urine, is excreted through the cloacal opening.

    Back to Main