Transcript Ch. 26: Metabolism

Chapter 26
Lecture Outline
26-1
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
Stable with equal energy intake and output
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around a homeostatic set point
Determined by combination of environmental and
hereditary factors
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26-2
30-50% of variation between individuals due to heredity
rest due to eating and exercise habits
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Appetite regulators
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short term
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 effects last minutes to hours
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long term
 effects last weeks to years
26-3
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Hunger – Ghrelin
Satiety
 Peptide YY
 Cholecystokinin (CCK)
Satiety
 Leptin
 Insulin
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Ghrelin – hunger
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from parietal cells of empty stomach
Peptide YY (PPY) – satiety
from enteroendocrine cells in ileum and colon
 secreted in proportion to calories consumed
 acts as ileal break (slows stomach emptying)
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Cholecystokinin (CCK) – satiety
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26-4
from enteroendocrine cells of duodenum and jejunum
appetite-suppressing effect on brain
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Leptin – secreted by adipocytes in proportion to
body fat stores
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Insulin – pancreatic beta cells
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26-5
effect similar to leptin (but weaker)
26-6
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One calorie - amount of heat required to raise
temperature of 1 g of water 1 °C
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Fats contain about 9 kcal/g
Carbohydrates and proteins, about 4 kcal/g
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1000 calories is a kilocalorie or Calorie
sugar and alcohol are “empty” calories -- few nutrients
Substance used for fuel is oxidized primarily to make ATP
26-7
Definition - Ingested chemical used for growth,
repair or maintenance
 Macronutrients consumed in large amounts
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Micronutrients needed in small amounts
Recommended daily allowances (RDA)
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safe estimate of daily intake for standard needs
Essential nutrients can not be synthesized
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26-8
proteins, fats and carbohydrates
minerals, vitamins, 8 amino acids and 1-3 fatty
acids must be consumed in the diet
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26-9
Nearly all dietary carbohydrates come from plants
The RDA for carbohydrates is greater than for any
other nutrient
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Carbohydrates are found/stored in 3 places in body
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Most carbohydrate serves as fuel
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26-10
neurons and RBCs depend on glucose
Sugars do serve as structural components
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muscle and liver glycogen; blood glucose
nucleic acids, glycoproteins and glycolipids, ATP
Blood glucose carefully regulated by insulin and
glucagon
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Fibrous material that resists digestion
Fiber is important to diet (RDA is 30 g/day)
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Water-soluble fiber (pectin)
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 blood cholesterol and LDL levels
Water-insoluble fiber (cellulose, lignin)
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26-11
excess interferes with mineral absorption - iron
absorbs water in intestines, softens stool, gives it
bulk, speeds transit time
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Most of the body’s stored energy
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Fat-soluble vitamins (A,D,E,K) absorbed with dietary fat
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hydrophobic, contains 2X energy/g, compact storage
glucose and protein sparing (no protein utilized for energy)
ingest less than 20 g/day risks deficiency
Chemical precursors (cholesterol and fatty acids)
Structural
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26-12
phospholipids and cholesterol are components of plasma
membranes and myelin
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Should be less than 30% of daily calorie intake
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Most fatty acids synthesized by body
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animal origin -- meat, egg yolks and dairy products
found in nuts, seeds and most vegetable oils
Cholesterol
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26-13
Coconut and palm oil
Unsaturated fats
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essential fatty acids must be consumed
Saturated fats
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typical American gets 40-50%
found in egg yolks, cream, shellfish, organ meats and
other meats
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Lipids transported in blood as lipoproteins
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26-14
protein and phospholipid coat around a hydrophobic
cholesterol and triglyceride core
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Categorized into 4 groups by density
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more protein means higher density
26-15
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Form in absorptive cells of small intestine
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26-16
enter lymphatic system, then blood
transports ingested fat to cells
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VLDL
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produced by liver to transport lipids to adipose tissue for storage
when triglycerides removed become LDLs (mostly cholesterol)
LDL
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26-17
absorbed by cells in need of cholesterol for membrane repair or
steroid synthesis
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Production and function
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26-18
liver produces an empty protein shell
travels through blood, picks up cholesterol
delivers cholesterol to liver, for elimination in bile
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Desirable to maintain total cholesterol concentration
of < 200 mg/dL
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most cholesterol is endogenous
dietary restrictions lower blood cholesterol levels
 by 5% with restriction of dietary cholesterol
 by 15 to 20% with restriction of certain saturated fats
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26-19
vigorous exercise lowers blood cholesterol
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12-15% of body mass
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mostly in skeletal muscles
Functions
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muscle contraction
 movement of body, cells, cell structures
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cell membranes (receptors, cell identity, pumps)
fibrous proteins (collagen, keratin)
 structural
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globular proteins (antibodies, myoglobin, enzymes)
 functional
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26-20
plasma proteins: blood osmolarity and viscosity
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RDA - 44-60 g/day for meat eaters
RDA - 60-100 g/day for vegans
Nutritional value depends on proportions of
amino acids
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8 essential amino acids can not be synthesized
 isoleucine, leucine, lysine, methionine, phenylalanine,
threonine, tryptophan and valine
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26-21
Cells do not store surplus protein
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Animal proteins (meat, eggs, dairy) are “complete proteins”
Plant sources must be combined in the right proportions
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beans – have very little tryptophan or cysteine
rice – is deficient in isoleucine and lysine
Examples of protein combinations
Beans with a corn tortilla
 Lentils with rice
 Peanut butter on toast
 Soy protein is complete on its own
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26-22
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Positive nitrogen balance
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occurs in children; they ingest more than they excrete
promoted by growth and sex hormones
Negative nitrogen balance
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26-23
body proteins being broken down for fuel (muscle atrophy)
glucocorticoids promote protein catabolism in states of stress
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Calcium and phosphorus
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Phosphorus
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cofactors for enzymes
Iron - essential for hemoglobin and myoglobin
Chlorine - component of stomach acid (HCl)
Mineral salts
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26-24
phospholipids, ATP, CP, buffers, nucleic acids
Calcium, iron, magnesium and manganese
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bones and teeth
electrolytes; govern function of nerve and muscle cells;
regulate distribution of body water
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Vegetables, legumes, milk, eggs, fish and shellfish
Animal tissues contain large amounts of salt
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26-25
carnivores rarely lack salt in their diets
herbivores often supplement by ingesting soils
Recommended sodium intake is 1.1 g/day
Typical American diet contains 4.5 g/day
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Body synthesizes some vitamins from precursors
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niacin, vitamin A and D
vitamin K, pantothenic acid, biotin, folic acid
 produced by intestinal bacteria
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Water-soluble vitamins (C, B)
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Fat-soluble vitamins (A, D, E, K)
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26-26
absorbed with water in small intestine; not stored
absorbed with dietary lipids; stored
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Dietary carbohydrate burned as fuel within hours of
absorption (glucose catabolism)
C6H12O6 + 6O2  6CO2 + 6H2O
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26-28
Transfers energy from sugar to ATP
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Series of small steps to efficiently transfer energy
to ATP (reduces energy lost as heat)
Glycolysis (yields 2 ATP)
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Aerobic respiration (yields 34-36 ATP)
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completely oxidizes pyruvic acid to CO2 and H2O
Anaerobic fermentation (if no O2 available)
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26-29
glucose (6C) split into 2 pyruvic acid molecules (3C)
pyruvic acid reduced to lactic acid
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Capture energetic electrons from glucose
during its catabolism
NAD (nicotinamide adenine dinucleotide)
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FAD (flavin adenine dinucleotide)
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26-30
derived from niacin (Vitamin B3)
derived from riboflavin (Vitamin B2)
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Aerobic
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38 ATP
10 NADH
Anaerobic
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2 ATP
8 NADH
Yes
No
Which need
oxygen?
Yes
26-34
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Without oxygen, your muscles switch to lactic acid
fermentation.
Only 2 ATP are made (the glycolysis portion of the
pathway)
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Fate of pyruvic acid depends on oxygen availability
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In an exercising muscle, demand for ATP is greater than
oxygen supply; ATP produced by glycolysis
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Lactic acid travels to liver to be oxidized back to pyruvic
acid when O2 is available (oxygen debt)
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then stored as glycogen or released as glucose
Fermentation is inefficient, not favored by brain or heart
26-37
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Without oxygen, yeast fermentation produces CO2
and ethanol as waste products.
Only 2 ATP are made (the glycolysis portion of the
pathway)
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Read this section from pg 1029
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Hepatic cirrhosis
25-39
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Patient presentation
Malnutrition
 Ascites
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Gynecomastia
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Patient presentation
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vomiting blood
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Patient presentation
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confusion
confabulation
Thiamine deficiency
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Alcohol interferes with
absorption
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Patient presentation
confusion
 agitation
 termors
 fever
 hallucinations
 paranoia
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Delirium tremens
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“the DTs”
caused by acute
alcohol withdrawal
may be fatal
1 out every 10 American men
between 18 and 29 is an
alcoholic
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Antabuse (Disulfiram) is used to treat alcoholism
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Causes an “instant hangover” if patient drinks alcohol
Notify doctor attending to patient
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ATP is quickly used after it is formed - it is not a storage
molecule
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Glycogenesis -- synthesis of glycogen
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stimulate by insulin
Glycogenolysis -- glycogen  glucose
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extra glucose will be stored
stimulated by glucagon and epinephrine
only liver cells can release glucose back into blood
Gluconeogenesis -- synthesis of glucose from
noncarbohydrates, such as fats and amino acids
26-46
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Triglycerides are stored in adipocytes
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constant turnover of molecules every 3 weeks
 released into blood, transported and either oxidized or redeposited in
other fat cells
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Lipogenesis = synthesizing fat from other sources
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amino acids and sugars used to make fatty acids and glycerol
Lipolysis = breaking down fat for fuel
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26-47
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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Amino acid pool
Dietary amino acids plus
100 g of tissue protein
broken down each day into
free amino acids
As fuel - first must be
deaminated (removal of
NH2)--what remains enters
the citric acid cycle
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26-48
the NH2 becomes ammonia
(NH3) which is toxic and
which the liver converts to
urea (excreted in urine)
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Liver converts
ammonia (NH3) to
urea which is
removed from
blood by kidneys
This is called the
ornithine cycle.
26-49
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Lasts about 4 hours during and after a meal
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Carbohydrates
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blood glucose is available to all cells for ATP synthesis
excess is converted by liver to glycogen or fat
Fats
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time of nutrient absorption and use for energy needs
taken up by fat cells from chylomicrons in the blood
primary energy substrate for liver, fat and muscle cells
Amino acids
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26-50
most pass through the liver and go onto other cells
in liver cells, may be used for protein synthesis
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Regulated by insulin secreted in response to elevated
blood glucose and amino acid levels and the hormones
gastrin, secretin and cholecystokinin (CCK)
Insulin
increases the cellular uptake of glucose by 20-fold
 stimulates glucose oxidation, glycogenesis and lipogenesis but
inhibits gluconeogenesis
 stimulates active transport of amino acids into cells and
promotes protein synthesis
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26-51
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Homeostasis of blood glucose critical to brain
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Carbohydrates
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glucose is drawn from glycogen reserves for up to 4 hours and
then synthesized from other compounds
Fat
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when stomach and small intestine are empty- stored fuels are
used
adipocytes and liver cells convert glycerol to glucose
free fatty acids are oxidized by liver to ketone bodies
Protein metabolism
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26-52
used as fuel when glycogen and fat reserves depleted
wasting away occurs with cancer and other diseases from loss
of appetite and altered metabolism
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By sympathetic nervous system and glucagon
Blood glucose drops, glucagon secreted
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26-53
glycogenolysis and gluconeogenesis raise glucose levels
lipolysis raises free fatty acid levels
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Promotes glycogenolysis and lipolysis under
conditions of injury, fear, anger and stress
Adipose, liver cells and muscle cells respond to
epinephrine
Cortisol promotes increased blood glucose
Fat and protein catabolism and gluconeogenesis
More about this when we study the
endocrine system
26-54
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Amount of energy used in the body in a given
period of time (kcal/hr or kcal/day)
Basal metabolic rate (BMR)
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Factors affecting total MR
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relaxed, awake, fasting, room comfortable temperature
pregnancy, anxiety, fever, eating, thyroid hormones, and
depression
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26-56
Homeostasis requires heat loss to match heat gain
Hypothermia - excessively low body temperature
Hyperthermia - excessively high body temperature
Thermoregulation - ability to balance heat
production and heat loss
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“Normal” body temperature varies about 1.8
degrees F. in a 24-hour cycle
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Core body temperature is temperature of organs in
cranial, thoracic and abdominal cavities
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low in morning and high in late afternoon
rectal temperature is an estimate of core temperature
adult varies normally from 99.0 - 99.7 degrees F.
Shell temperature is temperature closer to the
surface (oral cavity and skin)
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26-57
adult varies normally from 97.9 - 98.6 degrees F.
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26-58
Comes from energy-releasing chemical reactions
such as nutrient oxidation and ATP use
Exercise greatly increases heat production
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Radiation - loss of body heat to objects around us
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Conduction and convection - loss of body heat to
the air which when warmed rises to be replaced by
cooler air
Evaporation - heat loss as sweat evaporates
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26-59
caused by molecular motion producing infrared radiation
extreme conditions as much as 2L of sweat lost per hour,
dissipating heat by as much as 600 kcal/hour
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A part of your brain, the hypothalamis
monitors the temperature of blood
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Too warm
 cutaneous vasodilation
 sweating
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Too cold
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cutaneous vasoconstriction
arrector pili muscle contraction
shivering thermogenesis (if needed)
nonshivering thermogenesis -  thyroid hormone
and BMR (seasonal adjustment)
Behavioral thermoregulation
Examples?
26-60
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Fever
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Hyperthermia - exposure to excessive heat
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protective mechanism that elevates BMR which produces
more heat elevating the BMR, etc.
heat cramps are muscle spasms due to electrolyte imbalance
from excessive sweating
heat exhaustion -- severe electrolyte imbalance producing
fainting, dizziness, hypotension
heat stroke -- body temperature > 104 °F, may cause delirium,
convulsions, coma, and death
Hypothermia - exposure to excess cold
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26-61
as core body temperature , BMR  causing a further body
temperature decrease, etc. (fatal if body temperature  75 °F)