Chapter 3.6 - The Liver and Digestive System

Abstract

The entire human digestive tract stretches from the mouth to anus. In the mouth, salivary gland Amylase cleaves starchy sugars like those in potatoes and rice down to glucose. The enzyme Ptyalin also cleaves these sugars down to the disaccharide maltose. From there food passes down the esophagus to the stomach. In the stomach, which has an acid pH, the enzyme Pepsin cleaves all proteins after the amino acids Phe, Trp, and Tyr. The enzyme Rennin curdles milk by cleaving the milk protein caseinogen into the insoluble protein casein after the stomach food passes into the alkaline duodenum. Here it meets a group of enzymes produced and secreted by the pancreas as pancreatic juice. This is Trypsin, which cleaves proteins at the amino acids Lys and Arg, and Chymotrypsin, which cleaves proteins at Trp, Tyr, Phe, Leu, and Met. The enzyme Lipase is also produced, which cleaves complex fats and triglycerides into fatty acids. Finally, the enzyme Nucleotidase is in pancreatic juice, which cleaved RNA and DNA down to their root nucleotides. Finally, the enzyme Nucleotidase in the pancreatic juice cleaves RNA and DNA down to their root nucleotides. Serial aminopeptidases and carboxypeptidase cleave amino acids in the cut-up proteins one amino acid at a time, starting at the amino terminal and carboxyl terminal of peptides, respectively. At this point, in the small intestine, most proteins have been cleaved to amino acids, most polysaccharides have been cleaved to monosaccharides, most lipid or triglycerides have been cleaved into fatty acids, and most DNA/RNA has been split into root nucleotides. Most of these root molecules are absorbed by the intestines into the blood. The liver has numerous functions, including detoxification of an ingested sustenance, protein synthesis, and production of biochemicals necessary for digestion. Its essential functions include glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production, and detoxification.