HMB 200: INTEGRATED METABOLISM IN MAMMALIAN TISSUES Course outline Integration of carbohydrate, lipid and protein metabolism in well-fed state: Metabolic changes in liver, adipose tissue and skeletal muscle in well fed state. Obesity. Starvation: Metabolic changes in liver, adipose tissue and skeletal muscle in starvation. Role of hormones. Diabetes mellitus: Chronic effects of diabetes mellitus, metabolic changes in diabetes mellitus. Metabolic pathways of erythrocytes. Mechanisms of muscle contraction. Introduction In the body, individual pathways of carbohydrate, lipid and protein metabolism or tissues or organs do not function in isolation. They are interrelated and they interact with each other. They form a community in which one pathway (organ) produce substrate to another pathway (organ). Apart from substrates, hormones and nervous system also act as links between pathways or organs. Since energy is vital for survival of organism as whole these pathways are directed to meet energy requirements under various conditions. The integration of these pathways to generate energy is largely controlled by hormones like insulin, glucagon and catecholamines. They control flow of substrates between pathways mainly by regulating enzyme activity. Changes in the levels of these hormones in plasma allow body to store energy and grow when food is available in plenty or to make stored energy available for utilization when food is not available. These hormones are also responsible for the conversion of body protein to fuel (glucose) when food is in short supply and usually this may be accompanied by weight loss. Integration of carbohydrate, lipid and protein metabolisms can occur in well-fed state, obesity, starvation, diabetes mellitus and in other conditions like stress, injury, surgery etc. Since the pathways of carbohydrate, protein and lipid metabolisms are inter connected, the disorders of one metabolism can affect other metabolism.
INTEGRATION OF CARBOHYDRATE, LIPID AND PROTEIN METABOLISM IN WELL-FED STATE Each tissue of the human body has a specialized function, reflected in its anatomy and metabolic activity. Skeletal muscle allows directed motion; adipose tissue stores and releases energy in the form of fats, which serve as fuel throughout the body; the brain pumps ions across plasma membranes to produce electrical signals. The liver plays a central processing and distributing role in metabolism and furnishes all other organs and tissues with an appropriate mix of nutrients via the bloodstream. The functional centrality of the liver is indicated by the common reference to all other tissues and organs as “extrahepatic” or “peripheral.” During digestion in mammals, the three main classes of nutrients (carbohydrates, proteins, and fats) undergo enzymatic hydrolysis into their simple constituents. This breakdown is necessary because the epithelial cells lining the intestinal lumen absorb only relatively small molecules.
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