AP BIOLOGY

Detailed explanation-1: -The proventriculus is the true stomach of the bird from which hydrochloric acid and pepsin (an enzyme) is secreted to aid in digestion. The gizzard is the oval organ composed of two pairs of thick red muscles. These muscles are extremely strong and are used to grind or crush the food particles.

Detailed explanation-2: -The proventriculus (also known as the true stomach) is the glandular stomach where digestion primarily begins. Hydrochloric acid and digestive enzymes, such as pepsin, are added to the feed here and begin to break it down more significantly than the enzymes secreted by the salivary glands.

Detailed explanation-3: -The primary function of the proventriculus is to secrete hydrochloric acid (HCl) and pepsinogen into the digestive compartments that will churn the ingested material through muscular mechanisms.

Detailed explanation-4: -The proventriculus is a glandular stomach producing digestive enzymes similar to the stomach in dogs and cats. In seed-eating species such as psittacine birds, chickens, and pigeons the ventriculus is extremely muscular and the mucosal surface is covered by a koilin layer (cuticle).

Detailed explanation-5: -Poultry naturally produces enzymes to aid the digestion of feed nutrients. However, they do not have enzyme to break down fibre completely and hydrolysis of non-starch polysaccharides (NSP) present in the cell wall of the grains. They need exogenous enzymes in feed to aid digestion.