Human Anatomy and Physiology - N. I. Fedyukovich 2003

Metabolism and Energy
Carbohydrate Metabolism

Up to 60% of human Energy Requirements are met by CARBOHYDRATES. Consequently, the Brain's METABOLISM/26.html">Energy Metabolism relies almost exclusively on glucose. Carbohydrates also perform a structural function, being Key Components of complex cellular structures (such as glycopeptides, Glycoproteins, Glycolipids, and lipopolysaccharides). They are divided into simple and complex carbohydrates. When broken down in the digestive tract, complex carbohydrates yield simple Monosaccharides, which are then absorbed from the intestines into the bloodstream. Carbohydrates enter The Human Body primarily through plant-based foods (bread, vegetables, grains, and fruits) and are stored mainly as Glycogen in The Liver and Muscles. An adult body contains about 400 g of glycogen. However, these reserves are easily depleted and are used primarily to meet immediate energy demands.

The formation and storage of glycogen are regulated by Insulin, a hormone produced by the Pancreas. Conversely, The breakdown of glycogen into glucose is stimulated by Glucagon, another pancreatic hormone.

Blood glucose levels and glycogen stores are also regulated by the Central Nervous system. Neural signals originating from Carbohydrate Metabolism centers are transmitted to Organs via the Autonomic nervous system. Specifically, impulses traveling from these centers along sympathetic nerves directly accelerate Glycogenolysis in the liver and muscles, as well as the release of adrenaline from the Adrenal Glands. Adrenaline facilitates The conversion of glycogen into glucose and enhances oxidative processes within Cells. Additionally, Hormones from the adrenal cortex, the intermediate lobe of the Pituitary Gland, and The Thyroid Gland play a significant role in regulating carbohydrate metabolism.

The optimal daily intake of carbohydrates is approximately 500 g, though this figure can vary significantly depending on the body's Energy Expenditure. It is important to note that carbohydrate, lipid, and Protein metabolism are closely interconnected within the body, allowing for mutual conversion within certain limits. This occurs because the Intermediary Metabolism of carbohydrates, Proteins, and fats generates common intermediates for all metabolic pathways. Acetyl-CoA serves as the primary end product of protein, fat, and Carbohydrate Catabolism. Through acetyl-CoA, the metabolism of these three Macronutrients feeds into The Tricarboxylic Acid Cycle, where oxidation releases about 70% of all transformation energy.

The final products of metabolism consist of a small number of simple compounds. Nitrogen is excreted in the form of nitrogenous compounds (primarily urea and ammonia), carbon as СО₂, and hydrogen as Н₂О.