Oesophagus: a muscular tube through which food is carried towards the stomach
Crop: a diverticulum of the oesophagus, used to store food so that birds can ingest larger quantities of locally abundant food.
Liver: the largest internal organ and has numerous functions, derived from an outpocketing of endoderm epithelium on the ventral duodenum from the caudal part of the foregut.
nearly all blood circulated around the abdomen flows back through the portal vein to the liver where it comes into contact with liver cells, ensuring the products of digestion are presented to the hepatic cells before entering general circulation
Proventriculus: secretes gastric juices that initiate digestion
Ventriculus (gizzard): has muscular walls to abrade and crush seeds or other hard materials.
Pancreas: a long, irregularly shaped gland in vertebrate animals that is located behind that stomach and is part of the digestive system. Secretes hormones into the bloodstream and digestive enzymes into the small intestine.
Intestine: the part of the digestive tract that extends from the stomach to the cloaca.
Caeca: a pair of blindsacs or lateral dilatations of the gut, marking the beginning of the rectum. Used to aid the digestive system of some birds to help the enzymatic breakdown of materials like cellulose.
Cloaca: common chamber and outlet into which the intestinal, urinary, and genital tracts open. Used to expel faeces and lay eggs.
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Digestive System
Bird bills and tongues are modified for a variety of feeding habits and food sources
Diverticulum of the oesophagus, known as the crop, which is used to store food so that the bird can ingest larger quantities of locally abundant food.
The crop of Columbidae produces ‘crop milk’ which is a cheesy secretion formed by the proliferation and sloughing of cells lining the crop.
The young pigeons are fed on the milk until they can feed on grain.
Cedar waxwings, vultures, and birds of prey use their oesophagus.
Crops are less well developed in insect feeding birds, and they therefore feed throughout the day on sparsely distributed food.
The proventriculus secretes gastric juices that initiate digestion.
The ventriculus (or gizzard) has muscular walls to abrade and crush seeds or other hard materials. Birds may swallow sand and other abrasive to aid digestion.
The bulk of enzymatic digestion occurs in the small intestine, aided by secretions from the pancreas and the liver.
Paired caeca may be located at the union of the large and small intestine.
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