DIGESTIVE SYSTEM OF BIRDS/AVES

DIGESTIVE SYSTEM OF BIRDS/AVES

Stomach

Esophagus

How do Birds Eat

What is Digestion?

The esophagus is large in diameter, particularly in birds that swallow large meals. Swallowing is accomplished by esophageal peristalsis, and in most birds appears to be aided by extension of the neck. Most but not all birds have a crop, which varies from a simple expansion of the esophagus to one or two esophageal pouches. Depending on the state of contraction of the stomach, food being swallowed is diverted into the crop, then later propelled into the stomach by waves of peristalsis in the crop.

Birds have a glandular stomach, or proventriculus, and muscular stomach or gizzard. The glandular stomach receives food from the esophagus, and secretes mucus, HCl and pepsinogen, similar to what is seen in the mammalian stomach. The gizzard is a disk shaped, very muscular and in many birds contains small stones that facilitate grinding of foodstuffs. One of the gizzard's two orifices receives ingesta from the glandular stomach and the other empties into the duodenum

Digestive System of Birds

Small Intestines

Birds have a small intestine that seems very similar to the small intestine of mammals. A duodenum, jejunum and ileum are defined, although these segments are not as histologically distinct as in mammals. The proximal small intestine receives bile from the liver and digestive enzymes from the pancreas, and the absorptive epithelial cells are decorated with essentially the same battery of enzymes and transporters as in mammals.

Large Intestine

Digestion is the mechanical and chemical breaking down of food into smaller components, to a form that can be absorbed.

The large intestine consists of a short colon and, typically, a pair of ceca. Short villi extend into the lumen of the colon, unlike what is seen in mammals. The cloaca is an expanded, tubular structure that serves as the common opening of the digestive, reproductive and urinary systems, which opens to the outside of the bird as the vent.

• Finding Food: Birds have different dietary preferences and find foods in different ways, but they are all opportunistic feeders and will often sample many different foods. More aggressive bird species will guard favored food sources, and some will cache food to store it for future meals. Once a bird has found food, the eating and digesting process can begin.
• Chewing and Swallowing: Birds have specialized bills to help them take bites, but they do not chew as humans do. Instead, birds will either swallow food whole, or if it is too large or awkward to directly swallow, they will break it into smaller pieces.
• Digestive Tract; Food-Esophagus-Proventriculous-Gizzard-small intestine-large intestine
• Waste: After digestion, any remaining material, both liquid and solid, food passes through the cloaca to be expelled from the bird's body. For many birds, waste products can also be expelled from the gizzard in the form of pellets – fur, bones, tough husks and other materials that cannot pass through the bird's intestines are compacted into a small ball of material and regurgitated through the bill.

CLASS AVES

NORHANA ADAM ABAS