Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 27 Nutrition and...

Mosby items and derived items © 2007, 2003 by Mosby, Inc.

Chapter 27Chapter 27Nutrition and MetabolismNutrition and Metabolism


Overview of Overview of Nutrition and MetabolismNutrition and Metabolism

Nutrition refers to the food (nutrients) humans eatNutrition refers to the food (nutrients) humans eat Malnutrition—a deficiency in the consumption of food, vitamins, Malnutrition—a deficiency in the consumption of food, vitamins,

and mineralsand minerals Categories of nutrientsCategories of nutrients

• Macronutrients—nutrients needed in large amounts (bulk nutrients)Macronutrients—nutrients needed in large amounts (bulk nutrients) Macromolecules such as carbohydrates, fats (lipids), and proteinsMacromolecules such as carbohydrates, fats (lipids), and proteins WaterWater Macrominerals—minerals needed in large quantity; for example, sodium, Macrominerals—minerals needed in large quantity; for example, sodium,

chloride, and calciumchloride, and calcium

• Micronutrients—nutrients needed in very small amountsMicronutrients—nutrients needed in very small amounts VitaminsVitamins Microminerals (trace elements)—minerals such as iron, iodine, zinc, that Microminerals (trace elements)—minerals such as iron, iodine, zinc, that

are needed only in very small quantitiesare needed only in very small quantities

Balance of nutrients is required for good health Balance of nutrients is required for good health (Figure 27-1 and 27-2)(Figure 27-1 and 27-2)


Overview of Overview of Nutrition and MetabolismNutrition and Metabolism

Metabolism—the use of nutrients—a process made Metabolism—the use of nutrients—a process made up of many chemical processes (Figure 27-23)up of many chemical processes (Figure 27-23)

Catabolism breaks food down into smaller molecular Catabolism breaks food down into smaller molecular compounds and releases two forms of energy—heat and compounds and releases two forms of energy—heat and chemical energychemical energy

Anabolism—a synthesis processAnabolism—a synthesis process

Both processes take place inside of cells continuously and Both processes take place inside of cells continuously and concurrentlyconcurrently

Chemical energy released by catabolism must be Chemical energy released by catabolism must be transferred to ATP, which supplies energy directly to the transferred to ATP, which supplies energy directly to the energy-using reactions of all cells (Figure 27-3)energy-using reactions of all cells (Figure 27-3)


CarbohydratesCarbohydrates

Dietary sources of carbohydratesDietary sources of carbohydrates Complex carbohydratesComplex carbohydrates

• Polysaccharides—starches; found in vegetables and grains; Polysaccharides—starches; found in vegetables and grains; glycogen is found in meatglycogen is found in meat

• Cellulose—a component of most plant tissue; passes through Cellulose—a component of most plant tissue; passes through the digestive system without being broken downthe digestive system without being broken down

• Disaccharides—found in refined sugar; must be broken down Disaccharides—found in refined sugar; must be broken down before they can be absorbedbefore they can be absorbed

• Monosaccharides—found in fruits; move directly into the Monosaccharides—found in fruits; move directly into the internal environment without being processed directlyinternal environment without being processed directly

Glucose—carbohydrate most useful to the human cell; Glucose—carbohydrate most useful to the human cell; can be converted from other monosaccharides (Figure 27-4)can be converted from other monosaccharides (Figure 27-4)


CarbohydratesCarbohydrates Carbohydrate metabolism—human cells catabolize most Carbohydrate metabolism—human cells catabolize most

of the carbohydrate absorbed and anabolize a small of the carbohydrate absorbed and anabolize a small portion of itportion of it Glucose transport and phosphorylation—glucose reacts with ATP to form Glucose transport and phosphorylation—glucose reacts with ATP to form

glucose-6-phosphate; this step prepares glucose for further metabolic glucose-6-phosphate; this step prepares glucose for further metabolic reactionsreactions

• This step is irreversible except in the intestinal mucosa, the liver, and the kidney This step is irreversible except in the intestinal mucosa, the liver, and the kidney tubulestubules

Glycolysis—the first process of carbohydrate catabolism; consists Glycolysis—the first process of carbohydrate catabolism; consists of a series of chemical reactions (Figure 27-5)of a series of chemical reactions (Figure 27-5)

• Glycolysis occurs in the cytoplasm of all human cellsGlycolysis occurs in the cytoplasm of all human cells

• An anaerobic process—the only process that provides cells with energy under An anaerobic process—the only process that provides cells with energy under conditions of inadequate oxygenconditions of inadequate oxygen

• It breaks down chemical bonds in glucose molecules and releases about 5% of It breaks down chemical bonds in glucose molecules and releases about 5% of the energy stored in themthe energy stored in them

• It prepares glucose for the second step in catabolism—the citric It prepares glucose for the second step in catabolism—the citric acid cycleacid cycle



Carbohydrate metabolism (cont.)Carbohydrate metabolism (cont.)

Citric acid cycleCitric acid cycle

• Two pyruvic acid molecules from glycolysis are converted to two Two pyruvic acid molecules from glycolysis are converted to two acetyl molecules in a transition reaction, losing one carbon acetyl molecules in a transition reaction, losing one carbon dioxide molecule per pyruvic acid molecule converteddioxide molecule per pyruvic acid molecule converted

• By end of transition reaction and citric acid cycle, two pyruvic By end of transition reaction and citric acid cycle, two pyruvic acids have been broken down to six carbon dioxide and six water acids have been broken down to six carbon dioxide and six water molecules (Figures 27-6 and 27-7)molecules (Figures 27-6 and 27-7)

• Citric acid cycle also called tricarboxylic acid (TCA) cycle because Citric acid cycle also called tricarboxylic acid (TCA) cycle because citric acid is also called tricarboxylic acidcitric acid is also called tricarboxylic acid

• Citric acid cycle formerly called Krebs cycle after Sir Hans Krebs, Citric acid cycle formerly called Krebs cycle after Sir Hans Krebs, who discovered this processwho discovered this process



Carbohydrate metabolism (cont.)Carbohydrate metabolism (cont.) Electron transport system (Figure 27-8)Electron transport system (Figure 27-8)

• High-energy electrons (along with their protons) removed during citric High-energy electrons (along with their protons) removed during citric acid cycle enter a chain of molecules that are embedded in the inner acid cycle enter a chain of molecules that are embedded in the inner membrane of the mitochondriamembrane of the mitochondria

• As electrons move down the chain, they release small bursts of energy As electrons move down the chain, they release small bursts of energy to pump protons between the inner and the outer membrane of the to pump protons between the inner and the outer membrane of the mitochondrionmitochondrion

• Protons move down their concentration gradient and across the inner Protons move down their concentration gradient and across the inner membrane, driving ATP-synthase (Figure 27-9)membrane, driving ATP-synthase (Figure 27-9)

Oxidative phosphorylation—the joining of a phosphate group to Oxidative phosphorylation—the joining of a phosphate group to ADP to form ATP by the action of ATP synthase ADP to form ATP by the action of ATP synthase (Figure 27-10 and 27-11)(Figure 27-10 and 27-11)




The anaerobic pathway—a pathway for the catabolism of glucose; The anaerobic pathway—a pathway for the catabolism of glucose; transfers energy to ATP using only glycolysis; ultimately ends with transfers energy to ATP using only glycolysis; ultimately ends with the oxidative phosphorylation of ATP (paying the “oxygen debt”) the oxidative phosphorylation of ATP (paying the “oxygen debt”) (Figure 27-12))(Figure 27-12))

Glycogenesis—a series of chemical reactions in which glucose Glycogenesis—a series of chemical reactions in which glucose molecules are joined to form a strand of glucose beads; a process molecules are joined to form a strand of glucose beads; a process that operates when the blood glucose level increases above the that operates when the blood glucose level increases above the midpoint of its normal range (Figures 26-13 and 26-14)midpoint of its normal range (Figures 26-13 and 26-14)

Glycogenolysis (Figure 27-15)—the reversal of glycogenesis; Glycogenolysis (Figure 27-15)—the reversal of glycogenesis; means different things in different cellsmeans different things in different cells

Gluconeogenesis (Figure 27-16)—the formation of new glucose; Gluconeogenesis (Figure 27-16)—the formation of new glucose; occurs chiefly in liveroccurs chiefly in liver



Carbohydrate metabolism (cont.)Carbohydrate metabolism (cont.) Control of glucose metabolism—hormonal and neural devices Control of glucose metabolism—hormonal and neural devices

maintain homeostasis of blood glucose concentration maintain homeostasis of blood glucose concentration (Figures 27-17 and 27-18)(Figures 27-17 and 27-18)

• Insulin—secreted by beta cells to decrease blood glucose level Insulin—secreted by beta cells to decrease blood glucose level (Figure 27-14)(Figure 27-14)

• Glucagon increases blood glucose level by increasing activity of enzyme Glucagon increases blood glucose level by increasing activity of enzyme phosphorylasephosphorylase

• Epinephrine—hormone secreted in times of stress; increases Epinephrine—hormone secreted in times of stress; increases phosphorylase activityphosphorylase activity

• Adrenocorticotropic hormone stimulates adrenal cortex to increase its Adrenocorticotropic hormone stimulates adrenal cortex to increase its secretion of glucocorticoidssecretion of glucocorticoids

• Glucocorticoids accelerate gluconeogenesisGlucocorticoids accelerate gluconeogenesis

• Growth hormone increases blood glucose level by shifting from Growth hormone increases blood glucose level by shifting from carbohydrate to fat catabolismcarbohydrate to fat catabolism

• Thyroid-stimulating hormone has complex effects on metabolismThyroid-stimulating hormone has complex effects on metabolism




Hormones that cause the blood glucose level to Hormones that cause the blood glucose level to rise are called hyperglycemicrise are called hyperglycemic

Insulin is hypoglycemic because it causes the Insulin is hypoglycemic because it causes the blood glucose level to decreaseblood glucose level to decrease


LipidsLipids

Dietary sources of lipidsDietary sources of lipids Triglycerides—the most common lipids—composed Triglycerides—the most common lipids—composed

of a glycerol subunit that is attached to three fatty acidsof a glycerol subunit that is attached to three fatty acids

Phospholipids—an important lipid found in all foodsPhospholipids—an important lipid found in all foods

Cholesterol—an important lipid found only in Cholesterol—an important lipid found only in animal foodsanimal foods

Dietary fatsDietary fats

• Saturated fats contain fatty acid chains in which there are no Saturated fats contain fatty acid chains in which there are no double bondsdouble bonds

• Unsaturated fats contain fatty acid chains in which there are Unsaturated fats contain fatty acid chains in which there are some double bondssome double bonds


LipidsLipids

Transport of lipids—they are transported in blood Transport of lipids—they are transported in blood as chylomicrons, lipoproteins, and fatty acidsas chylomicrons, lipoproteins, and fatty acids In the absorptive state, many chylomicrons are present In the absorptive state, many chylomicrons are present

in the bloodin the blood Postabsorptive state—95% of lipids are in the form Postabsorptive state—95% of lipids are in the form

of lipoproteinsof lipoproteins• Lipoproteins consist of lipids and protein and are formed Lipoproteins consist of lipids and protein and are formed

in the liverin the liver Blood contains three types of lipoproteins: very low density, Blood contains three types of lipoproteins: very low density,

low density, and high densitylow density, and high density Cholesterol lipoproteins associated with heart disease (Figure 27-19)Cholesterol lipoproteins associated with heart disease (Figure 27-19)

• Fatty acids are transported from the cells of one tissue to the cells of Fatty acids are transported from the cells of one tissue to the cells of another in the form of free fatty acidsanother in the form of free fatty acids


LipidsLipids

Lipid metabolismLipid metabolism Lipid catabolism—triglycerides are hydrolyzed to yield fatty acids Lipid catabolism—triglycerides are hydrolyzed to yield fatty acids

and glycerol; glycerol is converted to glyceraldehyde-3-phosphate, and glycerol; glycerol is converted to glyceraldehyde-3-phosphate, which enters the glycolysis pathway; fatty acids are broken down by which enters the glycolysis pathway; fatty acids are broken down by beta- oxidation and are then catabolized through the citric acid cycle beta- oxidation and are then catabolized through the citric acid cycle (Figure 27-20)(Figure 27-20)

Lipid anabolism consists of the synthesis of triglycerides, Lipid anabolism consists of the synthesis of triglycerides, cholesterol, phospholipids, and prostaglandinscholesterol, phospholipids, and prostaglandins

Control of lipid metabolism is through the following hormones:Control of lipid metabolism is through the following hormones:

• InsulinInsulin

• Growth hormoneGrowth hormone

• ACTHACTH

• GlucocorticoidsGlucocorticoids


Proteins Proteins

Sources of proteinsSources of proteins

Proteins are assembled from a pool of 20 different Proteins are assembled from a pool of 20 different amino acidsamino acids

The body synthesizes amino acids from other The body synthesizes amino acids from other compounds in the bodycompounds in the body

Only about half of the necessary types of amino Only about half of the necessary types of amino acids can be produced by the body; the rest are acids can be produced by the body; the rest are supplied through diet—found in both meat and supplied through diet—found in both meat and vegetablesvegetables


ProteinsProteins Protein metabolism—anabolism is primary, and catabolism Protein metabolism—anabolism is primary, and catabolism

is secondaryis secondary Protein anabolism—process by which proteins are synthesized by Protein anabolism—process by which proteins are synthesized by

ribosomes of cells (Figure 27-21)ribosomes of cells (Figure 27-21) Protein catabolism—deamination takes place in liver cells and forms an Protein catabolism—deamination takes place in liver cells and forms an

ammonia molecule, which is converted to urea and excreted in urine, and a ammonia molecule, which is converted to urea and excreted in urine, and a keto acid molecule, which is oxidized or converted to glucose or fat (Figure keto acid molecule, which is oxidized or converted to glucose or fat (Figure 27-22)27-22)

Protein balance—rate of protein anabolism balances rate of protein Protein balance—rate of protein anabolism balances rate of protein catabolismcatabolism

Nitrogen balance—amount of nitrogen taken in equals nitrogen in protein Nitrogen balance—amount of nitrogen taken in equals nitrogen in protein catabolic wastecatabolic waste

Two kinds of protein or nitrogen imbalance:Two kinds of protein or nitrogen imbalance:

• Negative nitrogen balance—protein catabolism exceeds protein anabolism; Negative nitrogen balance—protein catabolism exceeds protein anabolism; more tissue proteins are catabolized than are replaced by protein synthesismore tissue proteins are catabolized than are replaced by protein synthesis

• Positive nitrogen balance—protein anabolism exceeds protein catabolismPositive nitrogen balance—protein anabolism exceeds protein catabolism

Control of protein metabolism—achieved by hormonesControl of protein metabolism—achieved by hormones


Vitamins and MineralsVitamins and Minerals

Vitamins (Table 27-3)—organic molecules Vitamins (Table 27-3)—organic molecules necessary for normal metabolism; many attach necessary for normal metabolism; many attach to enzymes and help them work or have other to enzymes and help them work or have other important biochemical roles (Figures 27-24 important biochemical roles (Figures 27-24 and 27-25)and 27-25)

The body does not make most of the necessary The body does not make most of the necessary vitamins; they must be obtained through dietvitamins; they must be obtained through diet

• The body stores fat-soluble vitamins and does not store The body stores fat-soluble vitamins and does not store water-soluble vitaminswater-soluble vitamins


Vitamins and MineralsVitamins and Minerals

Minerals (Table 27-4)—inorganic elements or salts Minerals (Table 27-4)—inorganic elements or salts found in the earthfound in the earth

Attach to enzymes and help them work and function Attach to enzymes and help them work and function in chemical reactionsin chemical reactions

Essential to the fluid/ion balance of internal fluid environmentEssential to the fluid/ion balance of internal fluid environment

Are involved in many processes in the body such as muscle Are involved in many processes in the body such as muscle contraction, nerve function, hardening of bone, etc.contraction, nerve function, hardening of bone, etc.

Too large or too small an amount of some minerals Too large or too small an amount of some minerals may be harmfulmay be harmful

Recommended mineral intakes may vary over the lifespan Recommended mineral intakes may vary over the lifespan (Figures 27-26 and 27-27)(Figures 27-26 and 27-27)


Metabolic RatesMetabolic Rates

Metabolic rate means the amount of energy released Metabolic rate means the amount of energy released by catabolismby catabolism

Metabolic rates are expressed in two ways:Metabolic rates are expressed in two ways:

Number of kilocalories of heat energy expended per hour Number of kilocalories of heat energy expended per hour or per dayor per day

As normal or as a percentage above or below normalAs normal or as a percentage above or below normal

Basal metabolic rate—rate of energy expended under Basal metabolic rate—rate of energy expended under basal conditionsbasal conditions

Factors: size, body composition, sex, age, thyroid hormone, body Factors: size, body composition, sex, age, thyroid hormone, body temperature, drugs, other factors (Figures 27-28 through 27-31)temperature, drugs, other factors (Figures 27-28 through 27-31)


Metabolic RatesMetabolic Rates Total metabolic rate (Figure 27-28)—the amount of energy Total metabolic rate (Figure 27-28)—the amount of energy

used in a given timeused in a given time Main determinates:Main determinates:

• Basal metabolic rateBasal metabolic rate

• Energy used to do skeletal muscle workEnergy used to do skeletal muscle work

• Thermic effect of foodsThermic effect of foods

Energy balance and weight—the body maintains a state Energy balance and weight—the body maintains a state of energy balanceof energy balance Body maintains weight when the total calories in the food ingested equals Body maintains weight when the total calories in the food ingested equals

the total metabolic ratethe total metabolic rate Body weight increases when energy input exceeds energy outputBody weight increases when energy input exceeds energy output Body weight decreases when energy output exceeds energy inputBody weight decreases when energy output exceeds energy input In starvation, carbohydrates are used up first, then fats, then proteins In starvation, carbohydrates are used up first, then fats, then proteins

(Figure 27-32)(Figure 27-32)


Mechanisms for Regulating Mechanisms for Regulating Food Intake (Table 27-6)Food Intake (Table 27-6)

Hypothalamus plays a part in food intakeHypothalamus plays a part in food intake

Feeding centers in hypothalamus exert primary Feeding centers in hypothalamus exert primary control over appetitecontrol over appetite Appetite centerAppetite center

• Cluster of neurons in lateral hypothalamus that, if stimulated, Cluster of neurons in lateral hypothalamus that, if stimulated, brings about increased appetitebrings about increased appetite

• Orexigenic effects—factors that trigger appetiteOrexigenic effects—factors that trigger appetite

Satiety centerSatiety center

• Group of neurons in ventral medial nucleus of hypothalamus Group of neurons in ventral medial nucleus of hypothalamus that, if stimulated, brings about decreased appetitethat, if stimulated, brings about decreased appetite

• Anorexigenic effects—factors that suppress appetite (anorexia Anorexigenic effects—factors that suppress appetite (anorexia is loss of appetite)is loss of appetite)


The Big Picture: Nutrition, The Big Picture: Nutrition, Metabolism, and the Whole BodyMetabolism, and the Whole Body

Every cell in the body needs the maintenance Every cell in the body needs the maintenance of the metabolic pathways to stay aliveof the metabolic pathways to stay alive

Anabolic pathways build the various structural Anabolic pathways build the various structural and functional components of the cellsand functional components of the cells

Catabolic pathways convert energy to a Catabolic pathways convert energy to a usable form and degrade large molecules into usable form and degrade large molecules into subunits used in anabolic pathwayssubunits used in anabolic pathways


The Big Picture: Nutrition, The Big Picture: Nutrition, Metabolism, and the Whole BodyMetabolism, and the Whole Body

Cells require appropriate amounts of vitamins Cells require appropriate amounts of vitamins and minerals to produce structural and and minerals to produce structural and functional components necessary for cellular functional components necessary for cellular metabolismmetabolism

Other body mechanisms operate to ensure Other body mechanisms operate to ensure that nutrients reach the cellsthat nutrients reach the cells

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