Archive for the ‘stomach’ tag

Importance of Saliva   no comments

Posted at 5:12 pm in Teeth

In far from all cases are the teeth the best possible tools, and nature has not hesitated to substitute more perfect technical means for them. Many species of the prosobranchiate snails feed on mollusks which are rather large and enclosed in a hard shell. To make a hole in the shell with a radula would take weeks or even months, and the radula would wear out. Therefore, these snails use a specific saliva instead of teeth, which is a four-percent solution of sulphuric acid. Nor is this very strange, for if the glandular cells of man's stomach secrete hydrochloric acid, why should snails not make use of sulphuric acid?

The acid secreted by the snails is so strong that it hisses and effervesces when falling on marble. It dissolves the mollusk shells quite easily. When attacking their prey, the snails apply their saliva to the shell which loosens a small section of it. The preying snail then bores a hole with its radula, inserts its proboscis and is then able to enjoy eating the defenceless victim.

It is not always enough to crush food for it to pass easily into the gullet. This is why the 'preparatory shop' contains the large and small salivary glands for both the mechanical and chemical processing of food. Saliva performs many important functions, but the most important seems to be to wet each lump of food which otherwise would not pass into the oesophagus. Anyone who had a chance to observe the European pond tortoises was easily convinced of the importance of saliva. The pond tortoises have no salivary glands. They eat their prey in water, amply washing down each mouthful. But on land they are helpless since completely dry food sticks in their throats.

The saliva of most animals contains substances (enzymes) which are the first to act chemically on the food being taken in. Nature subsequently developed these properties, making saliva somewhat poisonous. This is necessary as numerous microorganisms, most of them harmful to the organism, may lodge in the moist membrane of the mouth and the remains of food stuck between the teeth.

Written by rickweak on January 4th, 2010

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Differences in Teeth Location   no comments

Posted at 4:50 pm in Teeth

Teeth are also extremely important to predatory fish. Sharks have jaws whose inside surface is studded with teeth. These are arranged in regular rows with the tips pointing backwards, thus allowing the shark to hold its prey securely. Of course, the teeth at the very front have to work the hardest and they wear out the most rapidly. Sharks, too, would have a bad time if their front teeth were not replaced by new ones. The fact is that the front teeth are in motion throughout the shark's life. Bent over like attacking soldiers, row after row, they slowly but steadily move towards the edge of the jaw. The front rows of old worn-out teeth gradually 'crawl' out and, after having taken a glance at the outside world, fall out, only to be replaced by the next ones. Having worked their share and become well worn-out, these teeth, in their turn, release themselves and those behind move up to replace them. This process continues until the shark dies. Some extinct fossilized sharks had teeth which had not fallen out and, although they were quite old, they had the front part of their snout studded with teeth. This ability to constancy renew its teeth means that a shark is Đ°ble to fight right up to old age.

When the teeth are used solely to crush food, they may be located in some place other than the mouth. In some cases it may even prove advantageous to move them from the 'preparatory' shop to some adjacent department. Fish of the carp family have a toothless mouth, but you would be well advised not to put your finger into the throat of such a fish for it is there that they have their teeth and where the initial processing of food is carried out.

Some predatory fish and sea turtles have their teeth in their gullet. These are not properly teeth but very sharp and sometimes rather large spikes which are necessary to prevent the prey, which is still alive, from getting away. A spike-studded gullet is very much like the skin of a hedgehog or spiny ant-eater. All the spikes point towards the stomach and the food can thus only move in that direction. There is no way back from the stomach.

Written by rickweak on January 2nd, 2010

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