Interactive Summaries

Chapter 3: Digestion and Absorption

Putting it All Together: Digestion and Absorption

The digestive process begins in the mouth. Chewing breaks food into smaller pieces, increasing the surface area available to enzymes. Saliva contains the enzyme which breaks down starch into small sugar molecules. In the mouth, saliva and mucus blend with the food to form a . This ball of chewed food then slides through the esophagus to the stomach. Once in the stomach the keeps the food from sliding back into the esophagus. creates an acidic environment in the stomach that kills many pathogenic bacteria and aids in the digestion of protein. When the chyme is ready to leave the stomach, about 30-40 percent of carbohydrate, 10-20 percent of protein, and less than of fat have been digested. absorption occurs in the stomach. In the small intestine most digestion takes place in the . Fats do not ususally mix with water but this process is facilitated by once it is released from the gallbladder into the duodenum. Nutrients absorbed through the intestinal lining pass into the interior of the villi. Each villus contains blood vessels and a . Most minerals with the exception of are absorbed in the small intestine. is produced by bacteria in the large intestine, but it is not absorbed. The remainder of is digested in the colon.

Nutrition and GI Disorders

A diet low in and high in is the most common cause of constipation. As people age, the colon develops small pouches that bulge outward through weak spots. This condition is known as . Eating a diet high in fiber can help prevent this condition. GERD occurs when the lower relaxes inappropriately. The esophagus has no protective mucous lining so acid can quickly damage it. Doctors recommend avoiding foods that can weaken this sphincter such as . The cause of IBS remains a mystery. Some foods that are often offenders are . Without treatment IBS . It is likely that a number of physical and psychosocial factors combine to trigger this disorder. After lung cancer, is the most common form of cancer in the United States. Research to date shows that diets high in vegetables and regular physical activity are the most significant factors in reducing risk of this type of cancer. Flatus composition depends largely on intake and the activity of the colon's bacterial population. The major cause of ulcers is , which creates ulcers by weakening the protective mucous coating around the lining of the stomach.

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