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is mainly produced in muscle cells and red blood cells. It forms when the body breaks down carbohydrates to use for energy when oxygen levels are low. Times when your body's oxygen level might drop include: During intense exercise, when you have an infection or disease. Oxidativephosphorylation is the metabolic pathway in which the mitochondria in cells use their structure, enzymes, and energy released by the oxidation of nutrients to reform ATP. Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism. Metabolism can be conveniently divided into two categories: Catabolism - the breakdown of molecules to obtain energy, Anabolism - the synthesis of all compounds needed by the cells. Regulation of metabolism depends on chemicals in the cells and signals from the nervous and endocrine systems. Some aspects of metabolism depend on time elapsed since the last meal. Insulin is a peptide hormoneproduced by beta cellsin the pancreas. It regulates the metabolismof carbohydratesand fatsby promoting the absorption of glucosefrom the blood to skeletal musclesand fat tissueand by causing fat to be stored rather than used for energy. Insulin also inhibits the production of glucose by the liver. Total energy expenditure is based on: Basal metabolic rate (60%), Physical activity (30–35%), Food-induced thermogenesis (5–10%). Basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting). Disorders- Scurvyis a disease caused by a diet that lacks vitamin C (ascorbic acid). Patients develop anemia, debility, exhaustion, edema (swelling) in some parts of the body, and sometimes ulceration of the gums and loss of teeth. Beriberiis a disease caused by a vitamin B1 (thiamine) deficiency. There are two types of the disease: wet beriberi and dry beriberi. Wet beriberi affects the heart and circulatory system. In extreme cases, wet beriberi can cause heart failure. Dry beriberi damages the nerves and can lead to a loss of muscle strength and eventually, muscle paralysis. Beriberi can be life-threatening if it isn’t treated. If you have access to foods rich in thiamine, such as beans, vegetables, meat,and whole grains, your chances of developing beriberi are low. Today, beriberi mostly occurs in people with alcoholism. Celiac diseaseis an immune reaction to eating gluten, a protein found inwheat, barley and rye. If you have celiac disease, eating gluten triggers an immune response in your small intestine. Over time, this reaction produces inflammation that damages the small intestine's lining and prevents absorption of some nutrients (malabsorption). Obesity is a complex disorder involving an excessive amount of body fat. It increases your risk of diseases and health problems, such as heart disease, diabetes and high blood pressure. Your nephrons help: Remove excess water, wastes and other substances from your blood. Return substances like sodium, potassium or phosphorus whenever any of these substances run low in your body. Each nephron is composed of two main structures: the glomerulus and renal (kidney) tubule.