digestive gland liver 1: A large very vascular glandular organ of vertebrates that secretes bile and causes important changes in many of the substances contained in the blood (as by converting sugars into glycogen which it stores up until required and by forming urea). 2: Any of various large compound glands associated with the digestive tract of invertebrate animals and probably concerned with the secretion of digestive enzymes. BTO:0000759 BrendaTissueOBO viscus