resumen biologia- excretion

Apuntes

• Subtopic: Excretion Excretion is defined as the removal of waste products of metabolism and substances in excess of requirements. All living cells have metabolic reactions occurring inside them, which often produce substances that cells do not need. These substances may be toxic and need to be removed. For example, in mammals, carbon dioxide is excreted from the lungs. Urea is a waste product produced in the liver in humans. Too much urea in the blood is toxic, and it is removed by the kidneys. The kidneys also remove excess water and ions from the blood and produce urine, which is a solution of urea and waste materials in water. Urine travels through the ureters into the bladder, where it is stored. When the sphincter muscle at the entrance of the urethra relaxes, urine flows out of the body through the urethra. Urea is produced by the liver from excess proteins and amino acids. When proteins are consumed, enzymes break down the protein molecules into amino acids during digestion. These amino acids are absorbed into the blood and transported to the liver via the hepatic portal vein. Amino acids that are needed are made into proteins in the liver or released into the blood. Th...