Food Appearance 14 - 03 - 2002

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Food Appearance Good day, We hope your week was good. Ready to carry on with the journey of food through the gastrointestinal tract? Letís go. Appropriation is the making of something into oneís own. Appropriating foods, then, is the act of taking food into the body. Our first contact with food is visual. Young children originally try to discover what is good to eat and what is not by sticking everything within their field of vision into their mouth. If it tastes good it is food and is swallowed. If not, it is spit out. Gradually, the child learns to recognize food items by sight. An orange is orange and is for eating and a ball is for knocking over breakable items. Very quickly, children learn to recognize food by visual cues alone, and adults soon take this aspect of food appropriation for granted. Visual appearance of food is an important part of the digestive process. People start to salivate at colourful pictures of food dishes. If the food is pretty and served in a visually pleasing manner, the amount of digestive juices secreted is greater than if the appears distasteful or if it is served in unpleasant surroundings. The body begins to respond immediately when food is being placed within the visual field. Notice that advertisements for steaks & hamburgers prominently feature salad with vegetables, their attractive colour of red, green and yellow to contrast with the unappealing brown & black colour of meat. Digestion, or lack of it, begins with the eyes. The nose is the next organ involved in the physiology of digestion. The fragrance of food stimulates the nerves, which in turn starts the salivation process. The eyes and the nose, then, are the first organs used in the process of digesting and assimilating food. It is important, therefore, that time be taken to appreciate and select food according to its appearance and smell. After food is chosen according to sight and smell, it is brought towards the mouth and saliva starts to secrete. The mouth is the first step in the digestion of food proper. All digestion of food can be viewed as two concurrent processes. 1) Mechanical, or the actual movement of food as it is broken down into smaller particles and 2) Chemical, or the splitting of food into its simple nutritive components. In the mouth, mechanical digestion is performed by the action of the teeth and tongue, while the saliva furnishes the first step of chemical digestion. The incisor teeth and the front of the mouth first bite food. Then the canine teeth (next to the front teeth) shred the fruit into smaller parts as it passed back to the bicuspids, which continue tearing it into smaller portions. Finally, the molar teeth (in the back of the mouth) finish the grinding and crushing of the food. Chewing increases the surface area of the food so that the digestive enzymes may more easily penetrate it. Chewing not only breaks the food down into more digestible particles, but it also stimulates nervous impulses that cause the secretion of gastric juices, and thus prepare the digestive system for the food to be swallowed. The front teeth, which tear and shred food, can exert a force of up to 36kg, while the grinding molars can apply 45 to 100kg of force against food particles! There are 3 pairs of salivary glands in the mouth. They continuously secrete saliva to keep the mouth from drying out. During the day, these glands produce from 1 to 1.5 liter of saliva. The saliva prepares the food by lubricating it with mucin, which gives it its slippery characteristic. The first digestive enzyme is called ptyalin and starts the digestion process of starches. Ptyalin helps convert starch to a sugar called maltose. Saliva also has a solvent action upon food. It is only after the food is somewhat dissolved that it can be tasted. Saliva has also an enzyme (lysozyme) that digests bacterial cell walls, thus killing certain microorganisms and acts as a cleansing factor as its constant flow helps to dissolve and remove particles from the teeth. From here, the tong gathers the food together into a small ball and then elevates the mass of food back into the pharynx of the throat. This is the first stage of swallowing and the beginning of the foodís journey down to the stomach. Next week we will see what happens next. Until then The Crazy Nut Team



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