Digestive System

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Post  FinchG on Sun Dec 11, 2011 4:27 pm

Digestive System

The digestive system of birds is complex for the size of most birds. A small bird can eat up to twenty percent of its body weight daily. Birds have an extremely high metabolism so to keep up with the requirements bird must eat a large amount of food. The digestive system of the bird begins with the beak and tongue. Evolution has eliminated the teeth in birds. Birds have a very strong beak. The beak and the tongue are modified according to the diet and the environment of the bird. Saliva lubricates the food much like in a human so that it can pass to the oesophagus. The oesophagus is a tube-like structure, which passes food in waves better known as peristalsis, to an organ known as the crop.

The crop separates birds from many animals because it is an organ that is exclusive to these animals. A crop's main function is to store food. It is like an extra fuel tank for the bird. The crop is located at the base of the neck and can be easily seen after a bird has just eaten. If the crop is large in size the bird is probably full. If the crop is deflated and has a flat appearance the bird has not eaten yet. The crop continuously supplies small amounts of the food to the stomach. The food passes from the crop to the stomach, the most active part of the digestive system of a bird. There are two parts to the stomach of a bird.

The first part is known as the proventriculus. This is the glandular portion of the stomach. This portion secretes digestive juices, which break down the food. The proventriculus joins a large muscular portion of the stomach known as the ventriculus, or more commonly known as the gizzard .The gizzard grinds up food even more. The gizzard contains gravel, or grit, which works alongside with muscles in grinding up food. In birds that ingest whole seeds a gizzard is very important. In these birds digestive enzymes alone cannot effectively break the seed hull. This is where the gizzard comes in to help. These birds require a large amount of grit in their diet.

After leaving the gizzard the food is passed on to the small intestine where it mixes with bile and enzymes. The enzymes help with the breakdown of sugars, fats and proteins. Bile from the liver breaks down the larger fat molecules. The nutrients are then absorbed and passed on to the blood stream. The liver of the bird has two equal lobes and is nestled next to the heart under the rib cage. Like in humans, the liver acts as a detoxifier, purifying toxins that enter the bloodstream and it recycles red blood cells, some which are used to create bile. In some birds the bile is stored in the gallbladder. In birds such as the budgie, and some members of the parrot family lack a gallbladder.

The pancreas in birds is located near the small intestine. The first function of the pancreas is to neutralize acids that are found in the mixture passed on from the stomach. If this does not occur serious damage could occur to the intestine of the bird. Another major function of the pancreas is to produce insulin so that all the bird's cells are supplied with glucose. Some birds have an appendix or cecum which helps in the digestion of grains and fibres. Whatever does not get digested is passed through the single opening in the urogenital system known as the cloacae or vent. The waste is excreted in the form of bird droppings. Birds tend to make droppings often because they have such a high metabolism and eat often. Seed eaters usually digest their food within three hours!


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