The process of digestion begins when food is taken into the mouth. Chewing breaks the food into smaller pieces, thereby exposing more surfaces to the saliva. Saliva itself has a double function, it moistens the food, so facilitating swallowing, and it contains ptyalin, which begin the conversion of starch into simple sugars. Digestion do not occur until the food passes down through the oesophagus into the stomach. The stomach has both chemical and physical function. The walls of the stomach, which are protected by a layer of mucus, secrete juices composed of several enzymes and hydrochloric acid. The most powerful enzyme is pepsin, which are protected by a layer of mucus, secrete juices composed of several enzymes and hydrochloric acid. In addition, during these chemical reactions waves contraction and relaxation, known as peristalsis, sweep the walls of the stomach. They churn the food particles into a semi-solid mass known as chyme.

    From the stomach, the chyme passes into the small intestine through the pyloric sphincter. Much undigested material is still present. Proteins have not been completely broken down, starches are still being converted into simple sugars, and fats remain in large globule. In the small intestine the process of digestion is completed by the action of bile, which is secreted by the liver and released by the pancreas, and erepsin and invertase, secreted by the walls of the small intestine. Food, which are still undigested pass on in a liquid state into the large intestine, and are now called feces.

    Absorption of the products of digestion takes place mainly through the wall of the small intestine. Its inner surface is covered with minute hair-like projections called vili. Each villus contains several bloods capillaries and a specialized lymphatic vessel, known as lacteal. Glucose, fructose, galactose and the amino acids are all absorbed directly into the blood by entering the blood capillaries inside the vili. Glycerol and the fatty acids, on the other hand, pass into lacteals. The lymph then carries the fat up to the left internal jugular vein, where it enters the bloodstream.



I. Answer these questions based on the text above.

  1. Where does the process of digestion begin?
    1. What is the function of chewing?
    2. What are the two functions of saliva?
    3. Where do the major processes of digestion occur?
    4. What is the chemical function of the stomach?
    5. What is the physical function of stomach?
    6. What does the first paragraph discuss?
    7. What is feces?
    8. What are lacteals?
    9. Which products of digestion are not absorbed directly into the bloodstream?


    II. Answer these following questions with your own words.

    1. Why does man need three meals a day, whereas a snake needs to eat once a week?
    1. Are there any differences between digestion process in human being and in animals? Explain it briefly!


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