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physio lab 2 - Introduction Metabolism is defined as the...

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Introduction Metabolism is defined as the sum of all the chemical reactions that occur in the body. Energy metabolism is the way the body stores and utilizes its energy. There are two main reactions that occur in a metabolic pathway: anabolic reactions use energy to make large bimolecular from smaller ones. The products are made for cells or tissues to perform their normal functions or for growth and repair. Catabolism is the opposite as it breaks down large biomolecules into small biomolecules to create energy. This energy can be used to drive other cellular reactions (40% is used to synthesize ATP) or it is used in heat production (60%) to maintain the body temperature. If there are extra biomolecules left over, they are converted to energy storage molecules to provide energy between meals. The activity and amount of enzymes present for the pathway, hormones, and compartmentation regulate metabolic pathways. Sometimes different reactions occur in different areas of the cell or the body. A well-known pathway is the metabolic reactions of glucose. Glucose can be used as energy for cells or it can be synthesized into glycogen and stored in the liver or skeletal muscle. Glucose is a monosaccharide and it is the form in which carbohydrates are transported throughout the bloodstream. If blood glucose levels decrease (i.e. between meals), glyogenolysis will ensure. In this process, glycogen is broken down to glucose in the liver only. Glycogen stored in the skeletal muscle can only be used by the muscle itself and cannot be used to regulate blood glucose levels because the muscle does not contain glucose-6-phosphate. This enzyme is essential in blood glucose regulation because it dephosphorylates the glucose and allows it to enter the bloodstream. The 1
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glucose supply in both the liver and skeletal muscles are only capable of meeting a few hours of energy demand. This means that other molecules must be utilized for energy. Proteins may be utilized for energy, but only during periods of starvation or extended exercise. Proteins are transported as amino acids through the bloodstream. When proteins are broken down, ammonia (NH 3 ) and CO 2 are produced as waste. The ammonia is expelled through urine as urea. Triglycerides roam through the bloodstream as lipoproteins which are small particles that contain both lipid and protein parts. In order for triglycerides to enter a cell, they must leave the lipoprotein by breaking down to fatty acids and monoglycerides through the action of lipoprotein lipase. As a result, the fatty acids enter the cells and the monoglycerides travel through the bloodstream to the liver to be metabolized. In the cell, the fatty acids are either oxidized to create energy or they are used to create new triglycerides. The newly produced triglyceride is then either broken down to its components, glycerol and fatty acids, to produce energy, or sent into the bloodstream so it can be utilized by other cells. When triglycerides are broken down, the process is known as lipolysis
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