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Chapter 26: Nutrition and Metabolism

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Ghrelin
this is secreted by parietal cells in the fundus of teh stomach, expecially when the stomach is empty
Peptide YY (PYY)
this is a member of a family of hormones related to neuropeptides Y
Cholecystokinin
is secreted by enteroendocrine cells in the duodenum and jejunum
Leptin
\is secreted by adipocytes throughout the body
Insulin
is secreted by the pancreatic beta cells
Arcuate Nucleus
brain center for appetite regulation
Neuropeptide Y
a potent appetite stimulant
Melanocortin
which inhibits eating
Hunger Contractions
begin soon after the stomach is emptied and increase in intensity over a period of hours
Kilocalorie
in biochemistry
Fuel
is oxidized solely or primarily to extract energy from it
Nutrient
is any ingested chemical that is used for growth, repair or maintenance of the body
Macronutrients
they must be consumed in relatively large quantities
Micronutrients
only small quatities are required
Recommended Daily Allowances (RDAs)
is a liberal but safe estimate of the daily intake that would meet the nutrtional needs of most healthy people
Essential Nutrients
it is essential that they be included in the diet
hypoglycemia
deficiency of blood glucose
Water-soluble Fiber
found in oats, beans, peas, carrots, brown rice, and fruits
Water-insoluble Fibers
apparently have no effect on cholesterol or LDLs
Glucose-sparing and Protein-sparing Effects
as long as enough fat is available to meet the energy needs of the tissues, protein is not catabolized for fuel and glucose is spared for consumption by cells that cannot use fat, such as neurons
Essential Fatty Acids
are those we cannot synthesize and there fore must obtain from the diet
Lipoproteins
tiny droplets with a core of cholesterol and triglycerides and a coating of proteins and phopholipids
lipoprotein Lipase
that hydrolyzes triglycerides into monoglycerides and free fatty acids
Essential Amino Acids
that we cannot synthesize: isoleucine, leucine, lysine, methionine, phenylalnine, threonine, tryptophan and valine
Inessential Amino Acids
not because the body doesn not require them buy because it can syntesize its own when the diet does not supply them
Complete Proteins
are those that rpobide all of the essential amino acids in the necessary proportions for human tissue growth, maintance and nitrogen balance
Incomplete Proteins
lack one or more essential amino acids
Net Protein Utilization
the percent of the amino acids in a protein that the human body uses
Nitrogen Balance
is a state in which the rate of nitrogen ingestion equals the rate of excretion
Positive Nitrogen Balance
indicates that body proteins are being broken down and used a sfuel
Water-soluble Vitamins
are absorbed with water from the small intestine, dissolve freely in the body fluids, and are quickly excreted by the kidneys
Fat-soluble Vitamins
are incorporated into lipid micelles in the small intestine and absorbed with dietary lipids
Hypervitaminosis
(vitamin excesses) also causes disease
Glycolysis
which splits a glucose molecule into two molecules of pyruvic acid
Anaerobic Fermentation
which occurs in the absence of oxygen and reduces pyruvic acid to lactic acid
Aerobic Respiration
which occurs in the presence of oxygen and oxidizes pyruvic acid to carbon dioxide and water
Body Weight
remains stable if energy intake and output are equal
Body Weight seems to have a Hoeostatic
set point
Combination of Environmental and Hereditary factors
30 - 50% of variation between individuals is due to heredity with the rest being eating and exercise habits
Phosphorylation
the enzyme hexokinase transfers an inorganic phophate group (Pi) from ATP to glucose, producing glucose 6-phophate (G6P)
Pyruvic Acid
3 carbon (C3) molecules
Priming
G6P is rearranged (isomerized) to form fructose 6-phophate, which is phophorylated again to form frutose1, 6-diphophate
Cleavage
the lysis part of glycolysis occurs when fructose 1, 6-diphophate splits into two 3-carbon molecules
Oxidation
each PGAL molecule is then oxidized by removing a pair of hydrogen atoms
Dephosphorylation
phosphate groups are taken from the glycolysis intermediates and transferred to ADP, phophorylating it to ATP
Matrix Reactions
because their controlling enzymes are in the fluid of the mitochondrial matrix
Membrane Reactions
their controlling enzymes are bound to the membrane of the mitochondrial cristae
Proton Pump
that removes H+ from the mitochodrial matrix and pumps it into the space between the inner and outer mitochodrial membranes
Chemiosmotic Mechanism
which suggests the "push" created by the electrochemical H+ gradient
Efficiency
a ratio of energy output to input
Glycogenesis
teh synthesis of glycogen, is stimulated by insulin
Glycogenolysis
the hydrolysis of glycogen, releases glucose between meals when new glucose is not being ingested
Lipogenesis
synthesizing fats from other types of molecules
Lypolysis
breaking down fat for fuel
Beta-oxidation
which removes two carbon atoms at a time
Ketogenesis
two acetyl groups are condensed to form acetoacetic acid and some of this is further converted to B-hydroxybutyric acid and acetone
Amino Acid Pool
that cells can draw upon to make new proteins
Deamination
the removal of an amino group
Amination
the addition of -NH2;
Transamination
the transfer of -NH2 from one molecule to another
Absorptive (fed) State
lasts about 4 hours during and after a meal.
Postabsorptive (fastin) State
prevails in the late mornign, late afternnon and overnight
Metabolic Rate
means the amount of energy liberated in the body per unit of time, expressed in such terms as kcal/hr or kcal/day
Calorimeter
a closed chamber with water filled walls that absorb the heat given off by the body
Basal Metabolic Rate BMR
is a baseline or standard of comparison that minimizes teh effects of such variables
Total Metabolic Rate (TMR)
is the sum of BMR and energh expenditure for voluntary activities, especially muscular contractions
Hypothermia
an excessively low body temperature, can cause metabolism to slow down to the point that it cannot sustain life
Hyperthermia
an excessively high temperature, can disrupt the coordination of metabolic pathways and also lead to death
Thermoregulation
the balance between heat production and loss, is a critically important aspect of homeostasis
Core Temperature
the temperature of organs in the cranial, thoracic, and abdominal cavities
Shell Temperature
is the temperature closer to the surface, especially skin and oral temperature
Radiation
heat means molecular motion
Conduction
as the molecules of our tissues vibrate with heat energy, they collide with other molecules and transfer kinetic energy to them
Convection
the motion of fluid due to uneven heating
Evaporation
the cohesion of water molecules hampers their vibratory movement in response to heat input
Forced Convection
accelerates heat removal
Heat-losing Center
a nucleus still farther anterior in the hypothalamus
Heat-promoting Center
a more posterior nucleus
Nonshivering Thermogenesis
is a more long-term mechanism for generating heat , used especially in the colder seasons of the year
Behavioral Thermoregulation
behaviors that raise or lower the body's heat gains and losses
Heat Cramps
are painful muscle spasms that result from excessive electrolyte loss in the sweat
Heat Exhaustion
results from more severe water and electrolyte loss and is characterized by hypotension, dizziness, vomiting and sometimes fainting
Heatstrake
sunstroke
Appetite and satiety are contolled by
hypothalamus
Other Factors in Appetite Control
inflating the stomach with balloon inhibits hunger, amino and fatty acids stimulate release of CCK from small intestine (appetite suppressant), neuropeptide Y from hypothalamus is an appetite stimulant (it may be inhibited by leptin from "full" fat cells), different neurotransmitters stimulate desire for different kinds of food -- carboyhydrates, fats or protein
One Calorie
is amount of heat that will raise the temperature of 1 g of water 1 degree C. (1,000 calories is a kilocalorie in biochemistry)
Fat contain about
9 kcal/g when oxidized
Carbohydrates and proteins contain about
4 kcal/g
When a substance is used for fuel
it is oxidized solely or primarily to make ATP
Nutrients
are any ingested chemical used for growth, repair or maintenace -- water, carbohydrates, lipids, proteins, minerals, vitamins
Macronutrients
must be consume in large amounts -- proteins, fats and carbohydrates
Micronutrients
are needed only in small amounts
Recommended Daily Allowances (RDA)
is safe estimate of daily intake that meets standard needs (minimums)
Essential Nutrients
are those the body can not synthesize- minerals, vitamins, 8 amino acids and 1-3 fatty acids must be consumed in the diet
Carbohydrates
in 3 places in the body - muscle and liver glycogena and blood glucose
Neurons and RBCs
depend on glucose almost exclusively
Fat is Oxidized
when glycogen and glucose levels are low (if incompletely oxidized produces ketone bodies and acidosis)
Sugars do serve as
Structural components
Blood Glucose
is carefully regulated through the actions of insulin and glucagon
Carbohydrates RDA
175 g/day
Dietary Carbohydrates come in 3 forms
monosaccharides, disaccharides, polysaccharides
Monosaccharides
glucose, galactose and fructose, arising from digestion of starch and disaccharides, normal blood sugar concentration ranges 70 to 110 mg/dL
Disaccharides
table sugar (sucrose)
Polysaccharides
starch, glycogen and cellulose
Nearly all dietary carbohydrates come from
plants
Dietary Fiber
all fibrous animal or plant material that resist digestion- cellulose, pectin, gums and lignins
Fiber is important to the diet
RDA is 30 g/day
insoluble Fiber
absorbs water in the intestines and thus softens the stool and gives it bulk speeding teh transit time
Pectin
is a water-soluble fiber found in oats, beans, carrots, fruits and brown rice and reduces blood cholesterol and LDL levels
Cellulose, himicellulose and lignin
are water-insoluble fibers having no effect upon cholesterol
Lipids
average adult male is 15% fat; female 25% fat, represents body's stored energy
Hydrophobic
contains almost no water, contains twic as much energy per gram and is thus more compact storage form
Fat-soluble Vitamins
A,D,E and K depend on dietary fat for their absorption by the intestine
Phopholipids and Cholesterol
are structural components of plasma membranes and myelin
Cholesterol
is precursor of steriods, bile salts and vitamin D
Fatty Acids
are precursors of prostaglandins and other eicosanoids
Lipids should be less than
30% of daily calorie intake- typical american gets 40-50% of calories from fat
Most Fatty Acids
can be synthesized by the body
Essential Fatty Acids
are those that must be consumed (linoleic, linolenic and arachidonic acids must be consumed)
Saturated Fats
are of animal origin-- meat, egg yolks and dairy products
Unsaturated Fats
are found in nuts, seeds and most vegetable oils
Cholesterol
is found in egg yolks, cream, shellfish, organ meats and other meats
Lipids
are transported in the blood as lipoporteins (keeps it suspended in plasma)
Lipoproteins
are categorized into 4 groups by their density: more protein means more dense
Lipoproteins Types
chylomicrons, high-density (HDLs), low-density (LDLs), very low-density (VLDLs)
Chylomicrons
are formed in the absorptive cells of teh small intestine, passes into the lymphatic system and into the blood, capillary surface enzymes hydrolyze the triglycerides, fatty acids and glycerol enter the fat cells to be resynthesized into triglycerides for storage, chylomicron remnant is degraded by liver
VLDLs
produced by the liver, transport lipids to the adipose tissue for storage
Desirable to maintain high levels of HDL
since it indicates cholesterol is being removed from the arteries
Desirable to maintain a low LDL concentration
signifies high rate of cholesterol deposition in arteries (smoking, saturated fats, coffee and stress increase LDLs)
Desirable to maintain total plasma cholesterol concentration of 200 mg/dL or less
most cholesterol is internally synthesized, but dietary restriction may lower blood cholesterol levels (vigorous exercise lowers blood cholesterol)
Proteins
c12-15% of body mass - mostly inskeletal muscles
Functions of Proteins
muscle contraction, ciliary and flagellar motility, structural role in all cell membranes (channels, pumps, etc...), fibrous proteins (collagen, elastin and keratin) globular proteins include antibodies, hormones, hemoglobin, enzymes, etc..., plasma proteins maintain blood osmolarity and viscosity
RDA
is 44-60 g/day depending on age and sex
Nutritional Value of a Protein
depends whether it supplies amino acids in the proportions needed- essential amino acids can not be synthesized
Cells do not store surplus
when a protein is to be synthesized, all the necessary amino acids must be present
Complete Proteins
supply all amino acids in right amounts
Nitrogen Balance
requires the rate of nitrogen (protein) ingestion equals the rate of excretion
Positive Nitrogen Balance
occurs in growing children since they ingest more than they excrete
Negative Nitrogen Balance
occurs if body proteins are being broken down for fuel (muscle atrophy)
Glucocorticoids
promote protein catabolism in states of stress
Calcium and phosphorus
make up the bones and teeth
Phosphorus
is part of many structural compounds
Calcium, Iron, Magnesium and Manganese
function as cofactors for enzymes
Iron
is essential for hemoglobin and myoglobin
Chlorine
is component of stomach acid (HCl)
Mineral Salts
function as electrolytes and govern teh function of nerve and muscle cells, regulating the distribution of water in the body
Vitamins
body synthesizes some vitamins from precursors (A,D, etc...)
Water-soluble Vitamins
are absorbed with water from the small intestine and are not stored (C and B)
C Promotes
hemoglobin and collagen synthesis
B Vitamins
are coenzymes or parts of coenzymes
Fat-soluble
are absorbed with dietary lipids- A is a component of teh visual pigments and important to epithelium, D promotes calcium absorption and bone minerlization, K is essential for prothrombin synthesis and clotting, E is an antioxidant
Dietary Carbohydrate
is burned as fuel within a few hours of absorption (glucose catabolism) C6H12O6 + 6O2 -> 6CO2 + 6H2)
Purpose of Carbohydrates Metabolism
is to transfer energy from glucose to ATP
Common Pathway of Carbohydrate Metabolism
through which fats and amino acids are also oxidized as fuel
Glucose Catabolism
must occur as a series of steps where small amounts of energy are transferred to ATP with the rest released as heat
Three Major Pathways
Clycolysis, anaerobic fermentation, aerobic respiration
Clycolysis
splits a glucose molecule into 2 pyruvic acids molecules
Anaerobic Fermentation
(in the absence of O2) reduces pyruvic acid to lactic acid
Aerobic Repiration
(in the presence of O2) - oxidizes pyruvic acid to CO2 and H2O
Enzymes
remove electrons a hydrogen atoms during glucose catabolism
NAD+
(nicoinamide adenine dinucleotide), derived from niacin (B vitamin), NAD+ +2H -> NADH + H+
FAD
(flavin adenine dinucleotide), derived from riboflavin FAD + 2H -> FADH2
Coenzymes
are reduced and temporary carriers of teh energy
Glycolytic Steps
Step 1- phosphorylation, step 2 and 3- priming, step 4- cleavage, Step 5- oxidation, steps 6 and 7- dephosphorylation, 4 ATP produced
Step 1= Phosphorylation
glucose that just entered cell has phophate added to it, prevents glucose from leaving
Step 4= Cleavage
modified glucose molecule is split into 2 three-carbon molecules, PGAL (glyceraldehyde 3-phosphate)
Step 5= oxidation
removes a pair of hydrogen atoms picked up by coenzymes NAD+
Steps 6 and 7= dephosphorylation
(phosphate groups are transferred to ADP to form ATP)
4 ATP produced, but
2 were used in steps 1 and 3
Anaerobic Fermentation
fate of pyruvic acid depends on whether or not oxygen is available
In an exercising muscle
demand for ATP> oxygen supply so ATP is produced by glycolysis
Glycolysis
can not continue once supply of coenzyme NAD+ is gone
NADH donates
a pair of electrons to pyruvic acid which reduces it to lactic acid --restoring NAD+
Lactic Acid Travels
to the liver to be oxidized back to pyruvic when O2 is available (oxygen debt), then stored as glycogen or released as glucose
Fermentation
is wasteful and not favored by brain or heart
Aerobic Respiration
most ATP is generated in the mitochondria, requiring oxyen as teh final electron acceptro
Principal Steps
Matrix Reactions, membrane reactions
Matrix Reactions
occurring in fluids of mitochondria
Membrane Reactions
whose enzymes are bound to the mitochondrial membrane
Three steps to
prepare pyruvic acid to enter citric acid cycle
Aerobic Respiration known as
formation of acetyl-coenzymes A
Matrix Reactions
steps 12 through 21 called the citiric acid cycle (also called the kreb's cycle or tricarboxylic acid (TCA)cycle)
Carbon Atoms of the Glucose
have all been carried away as CO2 and exhaled
The energy has been lost as heat or stored in the:
2 ATP, the 8 reduced NADH and 2 FADH2 molecules of teh matrix reactions and 2 NADH from glycolysis
Citric Acid Cycle
is also a source of substances for the synthesis of fats and nonessential amino acids
Membrane Reactions
purpose is to oxidize NADH and FADH2, transfer their energy to ATP and regenerate them
Reactions
carried out by series of compounds attached to inner mitochondrial membrane called electron transport chain
Hydrogen atoms from NADH and FADH2 are
split apart
Protons released into matrix and electrons
passed along the transport chain with energy being released in small amounts
Final Electron Acceptor is
oxygen: accepts 2 electrons and 2 H+ to form a water molecule
NADH Releases
its electron pairs as hydrogen atoms to the electron-transport system-generates enough energy to synthesize 3 ATP molecules per electron pair
FADH2 Releases
its electron pairs oa little further along the elctron-transport system- generates enough energy to synthesize 2 ATP
Energy Balance Sheet
from complete aerobic oxidation of glucose to CO2 and H2O produces 38 ATP per glucose molecules (efficiency rating of 40% --0 rest is body heat)
Glycogen Metabolism
ATP is quickly used after it is formed -- it is not a storage molecule - extra glucose will not be oxidized, it will be stored
Glycogenesis
synthesis of glycogen, stimulated by insulin (average adult contains 450 g)
Glycogenolysis
breakdown of glycogen into glycose, stimulated by glucagon and epinephrine
Gluconeogenesis
synthesis of glucose from noncarbohydrates, such as fats and amino acids
Triglycerides
are stored in adipocytes
Lipogenesis
synthesizing fat from other sources
Lipolysis
breaking down fat for fuel
Glycerol
is converted to PGAL and enters glycolysis
Fatty Acids
are broken down 2 carbons at a time to produce acetyl-6A (process is beta oxidation)
Fatty Acids are Catabolized
in the mitochondrial matrix by beta-oxidation (2 carbons removed at a time) -- the resulting acetyl group can be turned into actyl-CoA and fed into citric acid cycle
Excess acetyl Groups
can be metabolized by liver during ketagenesis -- the products are called ketone bodies
If body Rapidly Oxidizing fats
ketones build up leading to ketoacidosis
Some Cells can use acetoacetic acid for
their principal fuel (cardiac and renal crotex cells)
Protein Metabolism - as fuel-
first must be deaminated (removal of NH2) - - what remains is converted to pyruvic acid, acetyl-CoA or part of citric acid cycle
When Shortage of Amino Acids
the reverse occurs for protein synthesis
The NH2 become
ammonia (NH3) which is toxic and which the liver converts to urea (excreted in urine)
Nutrtional Absorptive State
lasts about 4 hours during and after a meal (time of nutrient absorption and use for energy needs), regulated by insulin secreted in response to elevated blood glucose and amino acid levels and teh hormones gastrin, secretin and cholecystokinin
Postabsorptive State
homeostasis of blood glucose levels critical to brain- when stomach and small intestine are empty and stored fuels are used, regulated by sympathetic nervous system and glucagon, sympathoadrenal effects- adipose, liver cells and muscle cells are richly innervated and respond to epinephrine from adrenal medulla
Metabolic Rate
amount of energy used int he body in a given period of time (kcal/hr or kcal/day)- measured indirectly by oxygen consumption
Basal Metabolic Rate (BMR)
relaxed, awake, fasting, room comfortable temperature, adult male BMR is 2000 kcal/day (slightly less female)
Factors Affecting total MR
pregnancy, anxiety, fever, eating, thyroid hormones and depression
Homeostasis requires
heat loss match heat gain
Hypothermia
is excessively lo body temperature
Hyperthermia
is excessively high body temperature
Thermoregulation
is the ability to balance heat production and heat loss
Normal Body Temperature
varies about 1.8 degrees F. in a 24 hour cycle- low in morning and high in late afternnon
Core Body Temperature
is temperature of organs in cranial, thoracic and abdominal cavities- adult varies normally from 99.0 - 99.7 degrees F
Shell Temperature
is temperature closer to the the surface (oral cavity and skin) - adult varies normally from 97.9 - 98.6 degrees F
Heat Production
most comes from energy- releasing chemical reactions such as nutrient oxidation and ATP use, most from brain, heart, liver, endocrine and muscles, exercise greatly increase heat production in muscle
Radiation
is loss of body heat to the objects around us
Conduction
is loss of body heat to the air which when warmed rises to be replaced by cooler air (carrying heat away by convection)
Evaporative
heat loss is heat loss as sweat evaporates
Hypothalamic Thermostat
monitors the temperature of teh blood and skin thermoreceptors
Signals heat-losing center in hypothalamus
cutaneous vasodilation promotes heat loss, triggers sweating
Signals heat- promoting center in hypothalamus
causes cutaneous vasoconstriction, stimulates arrector pili muscles to make hair stand on end, shivering thermogenesis- muscle contraction, nonshivering thermogenesis- increase thyroid hormone and increase BMR
Behavioral Thermoregulation
get out of sun or remove heavy clothing
Fever
normal protective mechanism that elevates BMR which produces more heat elevating the BMR, etc.
Hyperthermia
is exposure to excessive heat
Heat Cramps
are muscle spasm due to electrolyte imbalance from excessive sweating
Heat Exhaustion
severe electrolyte imbalance producing fainting, dizziness, hypotension
Heat Stroke
body temperature rises dangerously high and may cause coma, convulsions and death
Hypothermia
is exposure to excess cold- as core body temperature decrease, BMR decrease causing a further body temperature decrease, etc. (fatal if body temperature decrease 75 F