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Chapter 27: Nutrition and Metabolism

Chapter 27: Nutrition and Metabolism. OVERVIEW. Nutrition refers to the food (nutrients) we eat Malnutrition: a deficiency in the consumption of food, vitamins, and minerals Categories of nutrients Macronutrients: nutrients that the body needs in large amounts (bulk nutrients)

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Chapter 27: Nutrition and Metabolism

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  1. Chapter 27: Nutrition and Metabolism

  2. OVERVIEW Nutrition refers to the food (nutrients) we eat Malnutrition: a deficiency in the consumption of food, vitamins, and minerals Categories of nutrients Macronutrients: nutrients that the body needs in large amounts (bulk nutrients) Macromolecules such as carbohydrates, fats (lipids), proteins Water Macrominerals: minerals needed in large quantity (e.g., sodium, chloride, calcium) Micronutrients: nutrients needed in very small amounts Vitamins Microminerals (trace elements): minerals needed only in very small quantities (e.g., iron, iodine, zinc) Balance of nutrients is required for good health (Figures 27-1 and 27-2)

  3. Organic Chemistry: Biochemicals • Carbohydrates: composed of carbon, hydrogen, oxygen. • Divided into monosaccharides, disaccharides, polysaccharides • Example: glucose • Energy sources and structure • Lipids: composed mostly of carbon, hydrogen, oxygen. • Relatively insoluble in water. • Example: anabolic steroids • Functions: protection, insulation, physiological regulation, component of cell membranes, energy source • Proteins: composed of carbon, hydrogen, oxygen, nitrogen, sometimes iodine. • Example: insulin • Functions: regulate processes, aid transport, protection, muscle contraction, structure, energy • Nucleic Acids: composed of carbon, hydrogen, oxygen, nitrogen, phosphorus. • Examples: ATP, DNA, RNA

  4. Nutrition Overview • Nutrition is used for two things • Energy (ATP synthesis) • Building blocks for healing and continual homeostasis

  5. OVERVIEW Metabolism: the use of nutrients through many chemical processes (Figure 27-23) Catabolism breaks food down into smaller molecular compounds and releases two forms of energy: heat and chemical Anabolism: a synthesis process Both processes take place inside cells continuously and concurrently Chemical energy released by catabolism must be transferred to adenosine triphosphate (ATP), which supplies energy toward the reactions of all cells (Figure 27-3)

  6. pathWays to make ATP

  7. CARBOHYDRATES Dietary sources of carbohydrates Complex carbohydrates Polysaccharides: starches; found in vegetables and grains; glycogen is found in meat Cellulose: a component of most plant tissue; passes through the system without being broken down Disaccharides: found in refined sugar; must be broken down before they can be absorbed Monosaccharides: found in fruits; move directly into the internal environment without being processed directly Glucose: carbohydrate most useful to the human cell; can be converted from other monosaccharides (Figure 27-4)

  8. CARBOHYDRATES (cont.) Carbohydrate metabolism: human cells catabolize most of the carbohydrate absorbed and anabolize a small portion of it Glucose transport and phosphorylation: Once glucose is inside the cell, it reacts with ATP to form glucose-6-phosphate This step prepares glucose for further metabolic reactions This step is irreversible except in the intestinal mucosa, liver, and kidney tubules

  9. CARBOHYDRATES: METABOLISM Glycolysis: the first process of carbohydrate catabolism; consists of a series of chemical reactions (Figure 27-5) Glycolysis occurs in the cytoplasm of all human cells An anaerobic process: the only process that provides cells with energy under conditions of inadequate oxygen Breaks down chemical bonds in glucose molecules and releases approximately 5% of the energy stored in them Prepares glucose for the second step in catabolism—the citric acid cycle

  10. CARBOHYDRATES: METABOLISM (cont.) Citric acid cycle (Krebs cycle) Pyruvic acid (from glycolysis) is converted into acetyl coenzyme A (CoA) and enters the citric acid cycle after losing carbon dioxide (CO2) and transferring some energy to NADH Citric acid cycle is a repeating (cyclic) sequence of reactions that occurs inside the inner chamber of a mitochondrion; acetyl splits from CoA and is broken down to yield waste CO2 and energy (in the form of energized electrons), which is transferred to ATP, NADH, and reduced flavin adenine dinucleotide (FADH2)

  11. CARBOHYDRATES: METABOLISM (cont.) Citric acid cycle By end of transition reaction and citric acid cycle, two pyruvic acids have been broken down to six carbon dioxide and six water molecules (Figures 27-6 and 27-7) Citric acid cycle is also called the tricarboxylic acid cycle (TCA) because citric acid is also called tricarboxylic acid Citric acid cycle is also called the Krebs cycle after Sir Hans Krebs, who discovered this process

  12. CELL METABOLISM: CATABOLISM (cont.) Electron transport system (ETS) Energized electrons are carried by NADH and FADH2 from glycolysis and the citric acid cycle to electron acceptors embedded in the cristae of the mitochondrion As electrons are shuttled along a chain of electron-accepting molecules in the cristae, their energy is used to pump accompanying protons (H+) into the space between mitochondrial membranes Protons flow back into the inner chamber through ATP synthasein the cristae, and their energy of movement is transferred to ATP Low-energy electrons coming off the ETS bind to oxygen and rejoin their protons to form water

  13. CARBOHYDRATES: METABOLISM (cont.) Electron transport system (Figure 27-8) The ETC is where the MOST ATP is produced in the body High-energy electrons (along with their protons) removed during the citric acid cycle enter a chain of molecules embedded in the inner membrane of the mitochondria As electrons move down the chain, they release small bursts of energy to pump protons between the inner and outer membrane of the mitochondrion Protons move down their concentration gradient, across the inner membrane, driving ATP synthase (Figure 27-9) Oxidative phosphorylation: the joining of a phosphate group to adenosine diphosphate to form ATP by the action of ATP synthase (Figures 27-10 and 27-11) (vs. substrate level phosphorylation)

  14. Electron Transport Chain

  15. Overview of Cell Metabolism • Production of ATP necessary for life • ATP production takes place in the cytosol (anaerobic) and mitochondria (aerobic) • Anaerobic does not require oxygen. Results in lactic acid formation and very little ATP production. • Aerobic requires oxygen. Results in large amount of ATP.

  16. CARBOHYDRATES: METABOLISM (cont.) Cori cycle: circular pathway in which lactic acid produced by anaerobic respiration in skeletal muscles is carried to liver cells, where it is converted back to glucose and stored as liver glycogen or returned to the bloodstream, where the glucose may be taken up by muscle cells and used for respiration or stored as muscle glycogen (Figure 27-13)

  17. CARBOHYDRATES: METABOLISM (cont.) Glycogenesis: a series of chemical reactions in which glucose molecules are joined to form a strand of glucose beads (glycogen); a process that operates when the blood glucose level increases above the midpoint of its normal range (Figures 27-14 and 27-15) Done by all cells of the body but liver and muscle cells store the most glycogen; astrocytes in the BBB also store some glycogen

  18. CARBOHYDRATES: METABOLISM (cont.) Glycogenolysis: the reversal of glycogenesis; it means different things in different cells (Figure 27-16) Enzyme phospatase allows glucose monomers (from catabolized polymers (glycogen) made by glycogenesis) to be exported from the cell and into circulation. Phospatase is only found in hepatic, kidney and intestinal mucosa cells. Muscle cells don’t have phosphatase and can only break glycogen down into G6P for glycolysis Gluconeogenesis: the formation of new glucose from protein or fats, which occurs chiefly in the liver (Figure 27-17)

  19. CARBOHYDRATES: METABOLISM (cont.) • Control of glucose metabolism: hormonal and neural devices maintain homeostasis of blood glucose concentration (Figures 27-18 and 27-19) • Insulin: secreted by beta cells to decrease blood glucose level • Glucagon increases the blood glucose level by increasing the activity of the enzyme phosphorylase promoting glycogenolysis • Incretins: GI hormones that, in the presence of glucose in the gut, stimulate insulin release from the pancreas, thereby decreasing blood glucose levels (e.g., GLP-1, GIP)

  20. CARBOHYDRATES: METABOLISM (cont.) Epinephrine: hormone secreted in times of stress; increases phosphorylase activity, accelerating glycogenolysis of both liver and muscle cells Adrenocorticotropic hormone stimulates the adrenal cortex to increase its secretion of glucocorticoids Glucocorticoids accelerate gluconeogenesis by breaking down proteins Growth hormone increases blood glucose level by shifting from carbohydrate to fat catabolism Thyroid-stimulating hormone and thyroid hormones have complex effects on metabolism Some raise and some lower blood glucose Hormones that cause the blood glucose level to rise are called hyperglycemic Insulin is hypoglycemic because it causes the blood glucose level to decrease

  21. Lipids • Triglycerides (95%): used for energy to produce ATP or stored in adipose tissue, liver; most common lipids in the diet • Saturated fats: FA with a full compliment of Hydrodens attached • meat fats, whole milk, cheese, eggs • Unsaturated fats:FA’s with double bonds • olive and peanut oil • Cholesterol: steroid found in liver, egg yolks but not found in plants • Phospholipids: major components of plasma membranes • Linoleic acids: essential fatty acids. Found in seeds, nuts, legumes, grains and green leaves

  22. Uses of Lipids in the Body • Triglycerides: used to produce ATP, Excess stored in adipose tissue or liver. • Cholesterol: can be eaten or manufactured in the body. Component of plasma membranes, can be modified to form bile salts and steroids • Eicosanoids derived from fatty acids. Involved in inflammation, blood clotting, tissue repair, smooth muscle contraction. • Phospholipids: part of plasma membrane and used to construct the myelin sheath. Part of bile

  23. LIPIDS (cont.) Transport of lipids: transported in blood as chylomicrons, lipoproteins, and fatty acids In the absorptive state, many chylomicrons are present in the blood Postabsorptive state: 95% of lipids are in the form of lipoproteins Lipoproteins consist of lipids and protein and are formed in the liver Blood contains three types of lipoproteins: very low density, low density, and high density (VLDL, LDL, HDL) Fatty acids are transported from the cells of one tissue to the cells of another in the form of free fatty acids There is an increase in blood levels of fatty acids during diabetes or starvation

  24. LIPIDS (cont.) Lipid metabolism Lipid catabolism: triglycerides are hydrolyzed to yield fatty acids and glycerol; glycerol is converted to glyceraldehyde-3-phosphate, which enters the glycolysis pathway; fatty acids are broken down by beta-oxidation and catabolized through the citric acid cycle (Figure 27-21) When fat catabolism occurs at an accelerated rate, ketone bodies are formed (ketogenesis) Ketones can be used by the liver or transported to other tissues to enter the CA cycle Lipid anabolism consists of the synthesis of triglycerides, cholesterol, phospholipids, and prostaglandins Made from glycerol and FA or excess glucose or aa Most FA can be made by the body, but some must be provided by the diet (essential fatty acids)

  25. LIPIDS • Control of lipid metabolism is through the following hormones • Insulin • Growth hormone, Adrenocorticotropic hormone, Glucocorticoids increase fat catabolism when blood glucose is low • Fat is stored in adipose tissue when blood glucose levels are sufficient • Carbohydrates have a fat storing effect • Leptin – secreted by fat storing cells to regulate satiety and how fat is metabolized

  26. Proteins • Chains of amino acids • Types • Essential: must be obtained in diet • Nonessential: body can synthesize • Complete proteins: contain all necessary amino acids (meat, fish, poultry, milk, cheese, eggs) • Functions • Protection (antibodies), regulation (enzymes, hormones), structure (collagen), muscle contraction (actin, myosin), transportation (hemoglobin, ion channels)

  27. PROTEINS Sources of proteins Proteins are assembled from a pool of 20 different amino acids If one aa is absent then certain proteins cannot be synthesized The body synthesizes amino acids from other compounds in the body (nonessential Amino Acids) Only about half the necessary types of amino acids can be produced by the body; the rest are supplied through diet; found in both meat and vegetables (essential Amino Acids)

  28. PROTEINS • Protein metabolism: anabolism is primary and catabolism is secondary • Protein anabolism: process by which proteins are synthesized by ribosomes of the cells • Important because it constitutes major growth, reproduction, tissue repair and cell replacements • Protein catabolism: deamination takes place in the liver cells and forms an ammonia molecule, which is converted to urea and excreted in urine, and a keto acid molecule, which is oxidized by citric acid cycle or converted to glucose or fat (Figure 27-22)

  29. PROTEINS (cont.) Protein balance: the rate of protein anabolism balances the rate of protein catabolism Nitrogen balance: the amount of nitrogen taken in equals the nitrogen in protein catabolic waste A body in protein balance will also be in nitrogen balance Two kinds of protein or nitrogen imbalance Negative nitrogen balance: protein catabolism exceeds protein anabolism; more tissue proteins are catabolized than are replaced by protein synthesis (protein poor diet, starvation) Positive nitrogen balance: protein anabolism exceeds protein catabolism (large amounts of tissue being made in growth or pregnancy) Control of protein metabolism: achieved by hormones GH and testosterone = anabolic Glucocorticoids = catabolic Thyroid hormones can be either, depending on the situation

  30. Vitamins • Organic molecules that exist in minute quantities in food • Essential vitamins must be obtained by diet • Function as coenzymes or parts of coenzymes (combine with enzymes and make the enzyme functional) • Classifications • Fat soluble: A, D, E, K. Can be stored in fatty tissues to the point of toxicity. • Water-soluble: B, C, and all others. Remain short time then are excreted. • Antioxidants: prevent formation of free radicals. Free radicals are chemicals produced by metabolism that are missing electrons. They take electrons from chemicals in cells, damaging the cells. • Table 27-3 Major Vitamins

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