| [ Summary ] |
Three major nutrients are found in various forms of carbohydrates, fats or lipids, and proteins. These nutrients are digested by specific enzymes secreted from the digestive glands into simple forms ; mono- or disaccharides, fatty acids, and amino acids or oligo peptides. These simple nutrients are further digested by enzymes found in the brush border of intestinal epithelia. Subsequently, nutrients are both actively and passively absorbed through the intestines. Carbohydrates are metabolized to produce adenosine triphosphate as well as glycogen or fatty acids. Fatty acids together with carnitine are transported into the mitochondria to produce energy through beta oxidation. Amino acids are used to form various types of proteins. The carbon skeletons of amino acids such as alanine and glutamine are used to produce energy, especially in conditions involving catabolism or wasting. This breakdown leads to muscle wasting. Vitamins are found in water-soluble and fat-soluble forms. Accumulated fat-soluble vitamins sometimes cause toxicity in dialyzed patients. On the other hand, water-soluble vitamins generally cannot be stored in the body. Therefore, deficiencies of these vitamins may occur, although large amount of vitamin C ingestion may lead to oxalosis in patients with chronic kidney disease. |