Nutrients

1
Nutrients

• Ingested chemical used for growth, repair or
  maintenance
• Macronutrients consumed in large amounts
• proteins, fats and carbohydrates
• Essential nutrients can not be synthesized by the
  body and must be consumed in the diet
• Minerals
• Vitamins

2
Fuels for ATP Synthesis
3
Carbohydrates

• Found in 3 places in body
• muscle and liver store the polysaccharide
  glycogen
• blood glucose
• Most carbohydrate serves as fuel
• neurons and RBCs depend on glucose
• Sugars also serve as structural components of
  molecules
• nucleic acids, glycoproteins and glycolipids, ATP
• Blood glucose carefully regulated by the
  pancreatic hormones insulin and glucagon

4
Dietary Sources of Carbs

• Nearly all dietary carbohydrates come from plants
• monosaccharides glucose, galactose and fructose
• liver converts galactose and fructose to glucose
• normal blood sugar concentration ranges 70 to 110
  mg/dL
• disaccharides sucrose (table sugar), maltose
  and lactose
• polysaccharides starch (plant) and glycogen
  (animal)

5
Glucose Storage and Use
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Carbohydrate Metabolism

• Dietary carbohydrate burned as fuel within hours
  of absorption (glucose catabolism)
• C6H12O6 6O2 ? 6CO2 6H2O
• Transfers energy from sugar to ATP

7
Summary of ATP Production
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Glycogen Metabolism

• ATP is quickly used after it is formed (not
  stored)
• extra glucose will not be oxidized, it will be
  stored
• Glycogenesis
• synthesis of glycogen in liver and skeletal
  muscle
• average adult contains 450 g
• Glycogenolysis
• hydrolysis of glycogen into glucose
• Gluconeogenesis
• synthesis of glucose from noncarbohydrates

9
Lipids

• Average adult male 15 fat female 25 fat
• Diverse functions
• Structural
• phospholipids and cholesterol are components of
  plasma membranes and myelin
• Chemical precursors
• cholesterol - a precursor of steroids, bile salts
  and vitamin D
• fatty acids - precursors of various signaling
  molecules
• Energy storage
• contains 3 times more energy per molecule
  compared to glucose
• used as an energy source during times of glucose
  and protein sparing

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Dietary Sources of Fat

• Should be less than 30 of daily caloric intake
• typical American gets 40-50
• Most fatty acids synthesized by body
• essential fatty acids must be consumed
• Saturated fats
• animal origin
• meat, egg yolks and dairy products
• Unsaturated fats
• found in nuts, seeds and most vegetable oils
• Cholesterol
• found in egg yolks, cream, shellfish, and meat

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Lipid Transport in Body

• Lipids transported in blood as lipoproteins
• protein and phospholipid coat around a
  hydrophobic cholesterol and triglyceride core
• Categorized by density more protein higher
  density
• Chylomicrons least dense
• Very low-density (VLDLs)
• Low-density (LDLs)
• High-density (HDLs) most dense

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Chylomicrons

• Formed in small intestine during digestion
• first enter lymphatic system, then blood
• capillary blood vessels that supply tissues have
  lipoprotein lipase which hydrolyzes much of the
  triglycerides into free fatty acids (FFAs) and
  glycerol
• enter cells to be used for energy storage or
  lipid synthesis
• following hydrolysis, the remaining chylomicron
  remnant is taken up by the liver and degraded

13
Lipoprotein Processing
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VLDL, LDL and HDL

• VLDL
• produced by liver to transport lipids to adipose
  tissue for storage
• become LDLs after the triglycerides are removed
• LDL (bad fat)
• absorbed by cells in need of cholesterol for
  membrane repair or steroid synthesis
• high levels correlates with cholesterol
  deposition in arteries
• HDL (good fat)
• liver produces an empty protein shell
• travels through blood, picks up cholesterol
• delivers cholesterol to liver, for elimination in
  bile
• high levels indicate cholesterol is being removed
  from arteries

15
Lipids

• Triglycerides are stored in adipocytes
• constant turnover of molecules every 3 weeks
• released into blood, transported and either
  oxidized or redeposited in other fat cells
• Lipogenesis
• synthesizing fat from other sources
• amino acids and glucose used to make fatty acids
  and glycerol
• Lipolysis
• breaking down triglycerides for fuel
• catalyzed by hormone sensitive lipase
• glycerol is converted to PGAL and enters
  glycolysis
• fatty acids are broken down 2 carbons at a time
  to produce acetyl-CoA (beta oxidation)

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Lipogenesis and Lipolysis Pathways
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Ketogenesis

• Fatty acids catabolized into acetyl groups (by
  beta-oxidation in mitochondrial matrix) may
• enter citric acid cycle as acetyl-CoA
• undergo ketogenesis
• metabolized by liver to produce ketone bodies
• acetoacetic acid
• ?-hydroxybutyric acid
• acetone
• rapid or incomplete oxidization of fats raises
  blood ketone levels (ketosis) and may lead to a
  pH imbalance (ketoacidosis)

18
Proteins

• 12-15 of body mass (mostly in skeletal muscles)
• Amino acid pool - dietary amino acids plus
  cellular proteins broken down each day into free
  amino acids
• May be used
• to synthesize new proteins
• as fuel
• first must be deaminated (removal of NH2)
• NH2 converted to ammonia (NH3) which is toxic and
  which the liver converts to urea (excreted by the
  kidneys into urine)
• what remains is converted to pyruvic acid or
  acetyl-CoA
• during shortage of amino acids, the reverse
  occurs for protein synthesis

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Pathways of Amino Acid Metabolism
20
Absorptive State

• Lasts about 4 hours after consumption of a meal
• time of nutrient absorption and use
• Carbohydrates
• blood glucose is available to all cells for ATP
  synthesis
• excess is converted by liver to glycogen or fat
• Fats
• taken up by fat cells from the blood
• Amino acids
• taken up by all cells for protein synthesis
• excess used for fuel for ATP synthesis or for
  fatty acid synthesis

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Absorptive State
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Regulation of Absorptive State

• Mainly regulated by the pancreatic hormone
  insulin secreted in response to elevated blood
  glucose and amino acid levels
• Insulin causes a decrease in the blood glucose
  level
• stimulates the uptake of glucose out of the blood
  into skeletal muscle cells
• stimulates the uptake of glucose out of the blood
  into adipose cells and its subsequent conversion
  to glycerol which is stored in adipose as
  triglycerides
• stimulates the enzymatic conversion of glucose
  into glycogen (glycogenesis)

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Insulin Actions
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Postabsorptive State

• Period of time between absorptive states
• Homeostasis of blood glucose critical to brain
• when stomach and small intestine are empty the
  fuels stored during the absorptive state are used
• Carbohydrates
• glucose is drawn from glycogen reserves for up to
  4 hours and then synthesized from other compounds
• Fat
• fat and liver cells convert glycerol to glucose
• free fatty acids are oxidized by liver to ketones
• other cells use for energy-- leaving glucose for
  brain
• Protein metabolism
• used as fuel when glycogen and fat reserves
  depleted

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Postabsorptive State
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Regulation of Postabsorptive State

• Mainly regulated by the pancreatic hormone
  glucagon secreted in response to a decrease in
  the blood glucose level
• Glucagon causes an increase in the blood glucose
  level returning it to the set point
• stimulates lipolysis of triglycerides in adipose
  cells and the release of fatty acids into
  circulation
• stimulates glycogenolysis in the liver
• stimulates gluconeogenesis in the liver
• The glucose that is synthesized by the liver is
  transported out of the liver into the blood
  increasing the blood glucose level

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Body Weight

• Stable with equal energy intake and output
• around a homeostatic set point
• Determined by combination of environmental and
  hereditary factors
• 30-50 of variation between individuals due to
  heredity
• rest due to eating and exercise habits

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Appetite Regulators

• Hormones secreted from tissues/organs within the
  abdominal cavity target the hypothalamus to
  control appetite
• Short term effects last minutes to hours
• Ghrelin produces hunger
• Peptide YY satiety
• Cholecystokinin satiety
• Long term effects last weeks to years
• Leptin inhibits hunger
• Insulin inhibits hunger

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Short-term Appetite Regulators

• Ghrelin hunger
• from parietal cells of empty stomach
• also stimulates hypothalamus release of
• human growth hormone releasing hormone
• Peptide YY (PPY) satiety
• secreted from the small intestine during
  digestion
• secreted in proportion to calories consumed
• slows stomach emptying
• Cholecystokinin (CCK) satiety
• secreted from the small intestine during
  digestion
• appetite-suppressing effect on brain

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Long-term Appetite Regulators

• Leptin
• secreted by adipocytes in proportion to body fat
  stores
• Insulin
• secreted from the pancreas in response to
  elevated blood glucose

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Hypothalamus

• Hormonal appetite regulators control the
  hypothalamic secretion of
• neuropeptide Y (hunger)
• stimulated by gherlin
• inhibited by PYY, leptin, and insulin
• melanocortin (satiety)
• stimulated by leptin, and CCK

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Appetite Regulation
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Calories

• Substances used for fuel is oxidized to make ATP
• carbohydrates
• lipids
• proteins
• One calorie - amount of heat required to raise
  temperature of 1 g of water 1 C
• 1000 calories is a kilocalorie or Calorie
• Fats contain about 9 kcal/g
• Carbohydrates and proteins, about 4 kcal/g
• sugar and alcohol are empty calories
• contain few nutrients

34
Metabolic Rate

• Amount of energy used in the body in a given
  period of time (kcal/hr or kcal/day)
• measured directly in calorimeter (water bath)
• measured indirectly by oxygen consumption
• Basal metabolic rate (BMR)
• metabolic rate while relaxed, awake, and fasting
  in a comfortable room temperature
• adult male BMR is 2000 kcal/day (slightly less in
  female)

35
Body Temperature

• Normal body temperature varies about 1.8
  degrees F in a 24-hour cycle
• low in morning and high in late afternoon
• Core body temperature is temperature of organs in
  cranial, thoracic and abdominal cavities
• rectal temperature is an estimate
• adult varies normally from 99.0 - 99.7 degrees F
• Shell temperature is temperature closer to the
  surface (oral cavity and skin)
• adult varies normally from 97.9 - 98.6 degrees F

36
Body Heat and Thermoregulation

• Homeostasis requires heat loss to match heat gain
• Hypothermia - excessively low body temperature
• can slow metabolic activity and cause death
• Hyperthermia - excessively high body temperature
• can disrupt enzymatic activity and metabolic
  activity and cause death
• Thermoregulation - ability to balance heat
  production and heat loss

37
Heat Production and Heat Loss

• Production
• From brain, heart, liver, endocrine and muscles
  during energy-releasing chemical reactions such
  as nutrient oxidation and ATP use
• exercise greatly ? heat production in muscle
• Loss
• Conduction - loss of body heat to the air around
  the body
• Evaporation - heat loss as sweat evaporates
• extreme conditions as much as 2L of sweat lost
  per hour, dissipating heat by as much as 600
  kcal/hour

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Thermoregulation

• Hypothalamus receives signals from
  thermoreceptors of blood and skin
• Elevated body temperature causes
• cutaneous vasodilation
• sweating
• Depressed body temperature causes
• cutaneous vasoconstriction
• arrector pili muscle contraction
• shivering (if needed)
• nonshivering thermogenesis - ? thyroid hormone
  and ?BMR (seasonal adjustment)
• Behavioral thermoregulation
• get out of heat/cold, remove/add clothing