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Dylan Han(6) 2-5

Topic Chosen 1: Digestion
Topic Chosen 2: Issues on Sex

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Thursday, July 3, 2008
E-Learning Day 5: 3 July 2008

Today, I will be posting an answer to a question related to Digestion.

How do birds digest food?

Initially, from the little I knew about digestion in birds, I knew that birds did not have teeth and thus were not able to masticate their food before swallowing. I also knew that birds swallowed stones to aid their digestion, but did not know how it aided this process. Therefore, I decided to utilise the search engine http://google.com.sg/ and http://wikipedia.org/ to source for information on the subject.

On Google, I managed to find a website describing the digestion process for birds. Digestion starts from the beak, where the food first enters. The bird's beak varies on its diet. Most birds also have saliva to help make swallowing easier for birds. The bird uses the tongue and beak to manipulate the food for swallowing.

The food then travels down the oesaphagus before coming to the stomach, or else known as the proventriculus in birds. The oesaphagus has an enlarged area in most brids known as the crop, which allows for the storage of food. The birds sometimes use the crop for the food to soften before entering the stomach. Other birds, for example the osprey, regurgitates softened food from the crop to feed their young. The stomach consists of two parts, namely the proventriculus and the gizzard (also known as the ventriculus or muscular stomach). Cells in the proventriculus are able to produce special digestive enzymes, hydrochloric acid and mucus to digest the food. The partly broken down food materials then proceed to the gizzard, which grinds and breaks the food down. This is to allow the enzymes to break down the food more easily. Furthermore, small stones or grains of sand that were swallowed by birds are stored in the gizzard, and these help to grind the food. The food can be passed back to the proventriculus and vice versa for more complete digestion. The gizzard is also lined with a tough layer of keratin, which is a type of protein, to protect the muscles responsible for the grinding.

The small intestine absorbs water and nutrients from the food and digests the food. The pancreas develops enzymes that break down protein and fats in the small intestine. The bloodstream receives nutrients that are absorbed by the intestinal membrane. The remaining waste products are transferred to the cloaca, which is somewhat an avian equivalent of the human rectum, through the largely featureless large intestine before being expelled at the right time.


From this, I finally understood the reason why birds are said to swallow small rocks and grains of sand and have learnt more about the digestive system of birds, which appear to be slightly similar to that of the human's.


Avian digestive system:


Sources: