VPB 121: Veterinary Physiology - II (2+1)

OESOPHAGUS AND CROP

• Oesophagus is wide which connects the mouth region to the crop.
• The wall of the oesophagus is composed of four layers of tissue, the innermost being mucous membrane. 
• The mucous membrane is an important barrier to the entry of microbes.
• It secretes mucous to lubricate and to aid the passage of the food along the alimentary canal.
• The crop is a large dilation of the oesophagus located just prior to the oesophagus entering the thoracic cavity. In some birds there are two crops and carnivorous birds donot have crop.
• The crop provides the capacity to hold food for some time before the commencement of digestion. This capacity enables the bird to take its food as “meals” at time intervals and permits continuous digestion.

• The crop structure is similar to that of the oesophagus except there are no glands present in fowls.
• Ducks and geese have glands in the crop mucous membranes.
• In pigeons, the surface cells of the crop slough off during brooding to form pigeon’s milk - used to feed the baby pigeons in the nest.

• Inside the thoracic cavity, the oesophagus becomes the proventriculus very glandular part of the digestive tract often called as glandular stomach.