Glucose Anabolism
Glucose storage : as stated, when glucose is not needed immediately for ATP production it combines with other molecules of glucose to form Glycogen , a polysaccharide that is the only stored form of carbohydrate in our bodies. The formation of Glycogen is known as Glycogenesis . Insulin stimulates hepatocytes and skeletal muscle cells to carry out glycogenesis. The body stores about 500g of glycogen (25% liver, 75% skeletal muscle). When the body requires ATP, glycogen stored in the liver is broken down into glucose and released into the blood to be transferred to cells, where it will be catabolized by cellular respiration (described above). The process of splitting glycogen into its glucose subunits is known as Glycogenolysis . When the liver runs low on glycogen, we eat. If not, your body starts to catabolize triglycerides and proteins. Some is normal but excess does not happen unless you are starving – eating very few carbohydrates or have an endocrine disorder. The glycerol part of triglycerides, lactic acid, and certain amino acids can be converted in the liver to glucose by a process known as Gluconeogenesis (making glucose from non-carbohydrate sources). Gluconeogenesis is stimulated by Cortisol, the main Glucocorticoid hormone of the adrenal cortex; and by Glucagon from the pancreas.
Lipid Metabolism
Lipids are transported in watery blood by combining with proteins produced in the liver and intestine called Lipoproteins . There are several types of lipoproteins that have different functions, but all essentially transport vesicles. They provide pickup and delivery services to the body. Lipoproteins are categorized according to density which varies according to the ratio of lipids (low density) to protein (high density). There are 4 major classes of lipoproteins: Chylomicrons, Very Low-Density Lipoproteins (VLDL), Low-Density Lipoproteins (LDL), High-Density Lipoproteins (HDL).
1) Chylomicrons
1-2% proteins, 85% triglycerides, 7% phospholipid, 6-7% cholesterol, small number of fat- soluble vitamins. Form in the mucosal epithelial cells of the small intestine Transport dietary (ingested) lipids to adipose tissue for storage.
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