Digestion begins in the mouth with the secretion of saliva and its digestive enzymes. The stomach is a major organ of the gastrointestinal tract and digestive system. Carnivorous plants secrete enzymes into the digestive fluid they produce. The cells are filled with secretory granules containing the precursor digestive enzymes. Also of importance is the presence in saliva of the digestive enzymes amylase and lipase. Sponges do not have nervous, digestive or circulatory systems. These adenocarcinomas start within the part of the pancreas which makes digestive enzymes. Feathers have similar keratins and are extremely resistant to protein digestive enzymes. The cells in each acinus are filled with granules containing the digestive enzymes. Copper enters the body through the digestive tract. This drug also has the benefit of sparing the normal bacteria of the digestive tract. The pancreas plays a vital role in the digestive system. Saliva controls pH in this region of the digestive tract. Lactose intolerance can persist after the eradication of "Giardia" from the digestive tract. Gestation can predispose for certain digestive disorders.