Transcript Nutrition, Metabolism and Thermoregulation

Nutrition, Metabolism and
Thermoregulation
Metabolism of
Energy
containing
Nutrients
Nutrition
•
•
We eat, we digest, we absorb, then
what?
3 fates for food = nutrients
1) Most are used to supply energy for life
2) Some are used to synthesize structural or
functional molecules
3) The rest are stored for future use – love
handles!
Nutrition
Figure 24.1
Nutrition: The Recommendation
.
Nutrition for College Students
Four
Groups:
Grease
Salt
Sugar
Alcohol
Protein Nutrition
Essential amino acids are the 9 (out of ~20) that we cannot
synthesize in the liver by transamination; they must be
.
present in our diet. All amino acids can be broken
down for
ATP energy production.
Nutrition
• Summary of Carbohydrate, Lipid and Protein
Nutrients (Table 24.1, p945)
• Vitamins (Table 24.2, p948-941)
– Function as coenzymes
– Not made in body (xcept D by skin, some B&K by
intestinal bacteria)
– B vitamins
• Minerals (Table 24.3, p952-955)
– 4% body weight
– Ionized in body fluids/bound to organic compounds
(phospholipids, hemoglobin, Na+Cl-)
Metabolism
• All biochemical reactions in the body
• Balance between synthesis (anabolic) and breakdown
(catabolic) reactions
– Anabolism
• chemical reactions that combine simple, smaller
molecules into more complex molecules
• uses energy
• protein formation from amino acids
• carbohydrate formation from simple sugars
– Catabolism
• chemical reactions that break down complex organic
molecules into simpler ones
• releases energy
• proteins are broken down by various proteases
Metabolism (cont)
• Relationship of catabolism to anabolism
Metabolism (cont)
• Link between anabolism and
catabolism is ATP
– ATP energy is the “currency”
used in most cellular energy
exchanges
– Catabolic reactions provide the
ATP energy that most anabolic
reactions require
– Only about 10-30% of the energy
released by catabolic reactions
can be used
• most chemical energy is lost as
“waste heat”
• “waste heat” is not wasted; it is
essential in maintaining a constant
body temperature
• ATP
Metabolism (cont)
– Allows for transfer of small but useful amounts of
energy from one molecule to another
– Cell's entire amount of ATP is recycled approximately
every minute
– ATP is NOT for long term energy storage
• too reactive in the cell
• other molecules available for energy storage (neutral fats,
glycogen, creatine phosphate, etc.)
– About 8kg (17 lb) of ATP is produced every hour in an
average male
– Total amount of ATP present in the body at any time is
only about 50g (0.050 kg)
• ATP (cont)
Metabolism (cont)
– Energy is released by
breaking the third phosphate
group’s bond
– ATP  ADP + Pi
• a reversible reaction
• the energy released is
enough to drive anabolic
reactions
– ATP  ADP + CrP
• creatine provides energy
storage in skeletal muscle
• allows for more ATP to be
formed when O2 is less
readily available during
skeletal muscle contraction
ATP is composed of 3
things:
• The sugar ribose
• The base adenine
• 3 phosphate groups
These
phosphates are
the key to the
activity of ATP.
• Energy is stored by
adding a phosphate to
ADP
• ADP + Pi  ATP
• Energy stored (endogonic
/ endo thermic rxn)
• Energy is released by
breaking a phosphate
off ATP
• ATPADP + Pi
• Energy released
(Exogonic/exothermic
rxn)
Energy Production
• Energy is stored in chemical bonds
• Oxidation-Reduction (Redox) reactions:
– Oxidation component:
• also known as dehydrogenation reactions
• remove electrons from molecules
– decreases the energy remaining in the oxidized
molecule
– generally, 2e- (and 2H+) are removed
simultaneously
• Can also be the gain of oxygen
Energy Production (cont.)
•Reduction
component:
– addition of electrons
to a molecule
– increases the energy
of the reduced
molecule
• These 2 component
reactions are always
coupled: oxidationreduction reactions
Oxidation Is Losing Electrons, Reduction Is Gaining Electrons: OIL RIG
Electron Loss Means Oxidation: ELMO
Losing Electrons Oxidation, Gaining Electrons Reduction: LEO the lion. GER! or LEO says GER
Energy Production (cont.)
•
ATP Generation
–
Addition of phosphate to a
chemical compound is
phosphorylation
–
3 mechanisms for this:
1. Substrate level
phosphorylation – a highenergy phosphate group is
transferred directly from a
molecule to ADP to make ATP
For example, when the energy
stored on a high-energy
phosphate group on creatine
phosphate is transferred to
ADP to make ATP in skeletal
muscles
CK transfers a
high energy
phosphate
from creatine
phosphate to
ADP
Energy Production (cont.)
ATP Generation
2. Oxidative
phosphorylation
• electrons (H+)
removed from
molecules
• enzymes combine H+
with O2, releasing
enough energy for
ATP formation
3. Photo-phosphorylation
•
photosynthesis
Carbohydrate Metabolism
• General
– 80% of carbohydrates ingested contain glucose;
remainder: fructose, galactose
– glucose is the body's preferred carbohydrate
energy source
• Fate of carbohydrates -- depends on needs
of body cells
– ATP production
– Amino acid synthesis
– Glycogenesis
– Lipogenesis
– Excretion in urine (minimal)
Carbohydrate Metabolism (cont.)
• Glucose anabolism
– Glucose storage:
glycogenesis
• glycogen formation is
stimulated by insulin
• glucose not needed
immediately is stored in the
liver (25%) and in skeletal
muscle (75%)
– Glucose release:
glycogenolysis
• converts glycogen to
glucose
• occurs between meals,
stimulated by glucagon and
epinephrine
Carbohydrate Metabolism (cont.)
• Glucose anabolism (cont.)
– Formation of glucose from proteins & fats:
gluconeogenesis
• When blood glucose level is low, you eat; if glucose
remains low, body catabolizes some proteins and fats
• Stimulated by cortisol and thyroid hormone
– cortisol (glucocorticoids) mobilizes proteins, making
AA's available
– thyroid hormone mobilizes proteins (AA's) and may
mobilize lipids
• Epinephrine, glucagon, hGH also stimulate
• These five hormones are often referred to as the
“insulin antagonists.”
Glucose Catabolism
• Glucose oxidation is known as cellular
respiration
– Complete catabolism of each molecule of glucose
to CO2, H2O
– Maximum yield of 38 ATP molecules/glucose
• 38% of the energy present in a glucose
• excellent efficiency for a biological system
• the rest of the energy is “waste heat”
– 2 linked enzymatic pathways are involved in
glucose catabolism
• glycolysis
• Kreb’s cycle
• Cells make
ATP in an
organelle
called the
mitochondria
In eukaryotes, respiration occurs in 3
steps
1. Glyco lysis (sugar breaking)
2. Kreb’s Cycle (Citric Acid Cycle)
3. Electron Transport Chain
• Glycolysis occurs
in the cytosol of
the cell and makes
2 ATP.
• Glycolysis starts
with the
monosacchride
(sugar) glucose
• And uses the
coenzyme NAD+
• The Kreb’s cycle or (Citric Acid
Cycle) occurs in the matrix of the
mitochondria and makes 2ATP
• The electron
transport chain
occurs across the
inner membrane
of the
mitochondria.
• It makes 34 ATP
and requires
oxygen
• It only occurs in
eukaryotes
• Sometimes,
under an aerobic
(lack of oxygen)
conditions, like
strenuous
exercise,
eukaryotes
undergo
fermentation
• This is called
lactic acid
fermentation.
• Fermentation
does NOT make
energy
• It changes the
coenzyme
NADH+H+ back
to NAD+ for use
in glycolysis
• Prokaryotes do
not have
mitochondria
or ANY
membrane
bound
organelle.
• They carry out
respiration in
the cytosol
• Prokaryotes use
the
fermentation
process to
change the
coenzyme
NADH+H+ back
to NAD+
• Microorganism
fermentation
produces ethyl
alcohol and CO2
Glucose Catabolism Overview
C6H12O6  6CO2(waste) + 12H2O + 36-38ATP(useful energy)
Summary:
Carbohydrate Metabolic Reactions
Lipids
Beta oxidation breaks down
fatty acids to form acetyl
Coenzyme A.
Lipids are more reduced
(have fewer oxygens);
therefore, they have more
potential chemical energy
and can be more fully
oxidized as an energy fuel.
Therefore, we gain more
energy, gram for gram, from
fats than from
carbohydrates.
Lipogenesis and Lipolysis
Figure 24.14
Lipid Metabolism:
Synthesis of Structural Materials
• The liver:
– Synthesizes lipoproteins for transport of
cholesterol and fats
– Makes tissue factor, a clotting factor
– Synthesizes cholesterol for acetyl CoA
– Uses cholesterol to form bile salts
• Certain endocrine organs (ovaries, testes,
and adrenal cortex) use cholesterol to
synthesize steroid hormones
Protein Metabolism
Amino acids may be
deaminated and the resulting
“carbon skeletons” of
whatever composition, can be
entered into the glycolytic
or Krebs cycle pathways to
yield an energy harvest of
ATPS. The amino groups will
be joined with CO2 molecules
to form the nitrogenous
waste urea.
Summary:
Lipid and Protein Metabolic Reactions
Liver Metabolism
• Hepatocytes carry out over 500
intricate metabolic functions
• A brief summary of liver functions
– Packages fatty acids to be stored and
transported
– Synthesizes plasma proteins
– Forms nonessential amino acids
– Converts ammonia from deamination to
urea
– Stores glucose as glycogen, and
regulates blood glucose homeostasis
– Stores vitamins, conserves iron,
degrades hormones, and detoxifies
substances
Cholesterol
• Lipoproteins are classified as:
– HDLs – high-density lipoproteins have more
protein content
– LDLs – low-density lipoproteins have a
considerable cholesterol component
– VLDLs – very low density lipoproteins are
mostly triglycerides
Cholesterol
Plasma Cholesterol Levels
• The liver produces cholesterol:
– At a basal level of cholesterol regardless
of dietary intake
– Via a negative feedback loop involving
serum cholesterol levels
– In response to saturated fatty acids,
increase cholesterol production in liver
Non-Dietary Factors Affecting Cholesterol
• Stress, cigarette smoking, and coffee
drinking increase LDL levels
• Aerobic exercise increases HDL levels
• Body shape is correlated with
cholesterol levels
– Fat carried on the upper body is correlated
with high cholesterol levels
– Fat carried on the hips and thighs is
correlated with lower levels
The Daily Metabolic Cycle
• The body shifts back
and forth
physiologically
between the
absorptive state and
the postabsorptive
state.
• The absorptive state
occurs for
approximately 4 hours
after each regular
meal.
• The postabsorptive
state takes over until
the next meal can be
absorbed.
Regulation of Food Intake
• Weight management
– If energy consumption (food intake) equals
energy utilized (activity), then body weight
will remain constant
– Activity and consumption levels vary day to
day, but individuals keep relatively constant
weight for long periods of time
– Many individuals in affluent nations have an
imbalance between intake and use  obesity
Regulation of Food Intake
• Hypothalamus - complex integrating center receiving
sensory information from all parts of the body
• The arcuate nucleus contains several peptides that
influence feeding
–Neuropeptide Y (NPY)/
Agouti-related peptide
(AgRP) stimulate feeding
–Pro-opiomelanocortin
(POMC)/ cocaine- and
amphetamine-regulated
transcript (CART) inhibit
feeding
Regulation of Food Intake (cont.)
• The hypothalamus has several inputs
– Vagal inputs from the gut
• Distenstion
– Nutrients
• Blood glucose
• Blood amino acids
• Blood fatty acids
– Hormones
•
•
•
•
Insulin, CCK
Leptin – secreted by adipose cells
Glucagon, epinephrine
Ghrelin – secreted by stomach
– Temperature - high temp decreases appetite
– Social and psychological factors
Thermogenesis
Core and Shell Temperature
• Organs in the core
(within the skull,
thoracic, and abdominal
cavities) have the
highest temperature
• The shell, essentially
the skin, has the lowest
temperature
• Blood serves as the
major agent of heat
transfer between the
core and shell
• Core temperature
remains relatively
constant, while shell
temperature fluctuates
substantially (20C–
40C)
Mechanisms of Heat Exchange
• The body uses four
mechanisms of heat exchange
– Radiation – loss of heat in the
form of infrared rays
– Conduction – transfer of heat by
direct contact
– Convection – transfer of heat to
the surrounding air
– Evaporation – heat loss due to the
evaporation of water from the
lungs, mouth mucosa, and skin
(insensible heat loss)
• Evaporative heat loss becomes
sensible when body
temperature rises and sweating
produces increased water for
vaporization
Countercurrent Heat Exchange
• The body uses four mechanisms
of heat exchange
– Radiation – loss of heat in the form
of infrared rays
– Conduction – transfer of heat by
direct contact
– Convection – transfer of heat to the
surrounding air
– Evaporation – heat loss due to the
evaporation of water from the lungs,
mouth mucosa, and skin (insensible
heat loss)
• Evaporative heat loss becomes
sensible when body temperature
rises and sweating produces
increased water for vaporization
Mechanisms of Heat Exchange
• The body uses four mechanisms
of heat exchange
– Radiation – loss of heat in the form
of infrared rays
– Conduction – transfer of heat by
direct contact
– Convection – transfer of heat to the
surrounding air
– Evaporation – heat loss due to the
evaporation of water from the lungs,
mouth mucosa, and skin (insensible
heat loss)
• Evaporative heat loss becomes
sensible when body temperature
rises and sweating produces
increased water for vaporization
Role of the Hypothalamus
• The main thermoregulation center is the
preoptic region of the hypothalamus
• The heat-loss and heat-promoting centers
comprise the thermoregulatory centers
• The hypothalamus:
– Receives input from thermoreceptors in the skin
and core
– Responds by initiating appropriate heat-loss and
heat-promoting activities
Mechanisms of Body Temperature
Regulation
Hyperthermia
• Normal heat loss processes become
ineffective and elevated body
temperatures depress the hypothalamus
• This sets up a positive-feedback
mechanism, sharply increasing body
temperature and metabolic rate
• This condition, called heat stroke, can
be fatal if not corrected
Heat Exhaustion
• Heat-associated collapse after
vigorous exercise, evidenced by
elevated body temperature, mental
confusion, and fainting
• Due to dehydration and low blood
pressure
• Heat-loss mechanisms are fully
functional
• Can progress to heat stroke if the
body is not cooled and rehydrated
Fever
• Controlled hyperthermia, often a result of
infection, cancer, allergic reactions, or central
nervous system injuries
• White blood cells, injured tissue cells, and
macrophages release pyrogens that act on the
hypothalamus, causing the release of
prostaglandins
• Prostaglandins reset the hypothalamic
thermostat
• The higher set point is maintained until the
natural body defenses reverse the disease
process
Response to Heat
• Radiation away of infrared radiation
• Convection and conduction of heat to air or water
surrounding the body
• Evaporation from sweating and from ventilating
respiratory membranes
• Vasodilation of cutaneous capillary beds
• Decreased hormonal activity leading to decreased
basal metabolic rate (BMR)
• Behavioral: stop exercising; move to the shade,
take off clothes, turn on a/c, etc.
Response to Cold
• Increased hormone activity (thyroxine,
epinephrine) leading to increased (BMR)
• Increased sympathetic ANS activity leading to
increased (BMR)
• Shivering of skeletal muscles
• Vasoconstriction of dermal capillary beds
• Behavioral: start exercising, huddle together, use
clothing and shelter, use fire or other means of
heating the surroundings
Glucose Catabolism: Glycolysis
•
Occurs in cytosol
•
1 glucose 2 pyruvates
(pyruvic acid)
•
Net gain: 2 ATP’s
– 2 ATP’s used
– 4 ATP’s made
•
Net gain 2 NADH + 2H+
(aerobic conditions)
Oxidative Phosphorylation
• written by Greg Crowther and Do Peterson
• Do you see the athletes run?
Every soul beneath the sun -• You can't see inside their cells;
Small cigar-shaped organelles
• Matrix protons get pumped out
Then they take an inward route
• [Preacher's message:]
Fuel the muscles.
Feel the ATP.
See the athletes.
In the morning,
In the afternoon.
In the late night,
When I feel up,
When I'm movin' 'round,
When I stand up,
All right, now.
Oxidative phosphorylation.
Oxidative phosphorylation.
Do you see the children crawl?
Ox phos fuels them one and all.
If you could, here's what you'd see:
Synthesizing ATP.
To the intermembrane space.
Through the ATP synthase.
Feel the sunshine.
See the children.
Ox phos fuels us you and me.
In the mid-day,
In the evening,
Ox phos fuels us me and you.
When I feel good,
When I sit up,
When I make my sound.
Oxidative phosphorylation.
Oxidative phosphorylation....
Glucose, Glucose
•
written by Jeff Barry and Andy Kim; scientific lyrics by Greg Crowther
•
Glucose -- ah, sugar sugar --You are my favorite fuel From the blood-borne substrate
pool.
Glucose -- monosaccharide sugar --You're sweeter than a woman's kiss
'Cause I need you for glycolysis.
I just can't believe the way my muscles take you in. (For you, they'll open the door.)
All it takes is a little bit of insulin
(To upregulate GLUT4).
Ah, glucose -- ah, sugar sugar --You help me make ATPWhen my predators are chasing me.
Ah, glucose -- you're an aldehyde sugar,
And you're sweeter than a woman's kiss
'Cause I need you for glycolysis.
I just can't believe the way my muscles break you down.
(My glycogen is almost
gone.)
A few more seconds and I'll be rigor mortis-bound. (Acidosis done me wrong.)
Your sweet is turning sour, baby.
I'm losing all my power, baby.
I'm gonna make your muscles ache.
No, no, no!
I'm swimming in lactate, baby.
Yes, I'm swimming in lactate, baby.
Now I'm drowning in lactate, baby.
I'm gonna make your muscles ache.
No, no, no!
I'm drowning in lactate, baby.
Ah, glucose -- ah, sugar sugar -I used you up and you left me flat;
Now I'll have to get my kicks from fat.
Oh, glucose, glucose, sugar, sugar,
The honeymoon is over now.
•
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•
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Glucose Catabolism
• Fate of pyruvate depends on O2
– Without O2:
NADH + H+ + pyruvate  lactic
acid
– With O2:
• Pyruvate converted to acetyl
coenzyme A (acetyl CoA)
• This reaction couples
glycolysis to the Krebs cycle
Glucose Catabolism
• Pyruvic acid - formation of acetyl coenzyme A
(Acetyl CoA) + CO2
– lose one carbon from pyruvate to form CO2 (waste)
– the remaining two carbons, the acetyl group, join with
CoA, to generate NADH + H+ (1 from each pyruvate =
2 NADH + 2H+ total from one glucose)
Glucose Catabolism: Krebs Cycle
• Krebs cycle / Citric
Acid Cycle /
Tricarboxylic Acid
Cycle (TCA)
– Oxidation of acetyl
Coenzyme A
– Reduction of coenzymes
(NAD+, FAD+)
• Oxidative
phosphorylation
– Uses NADH2‘s and
FADH2‘s to make
additional ATPs
Glucose Catabolism
Glycolysis and
Krebs Cycle combined total:
6 CO2 (waste) + 6 H2O
10 NADH2 + 2 FADH2 +
4 ATP (energy harvest)
Glucose Catabolism: Oxidative
Phosphorylation
 Electrons Source: NADH2/FADH2 from glycolysis and Krebs
cycle
 High-energy electrons enter the system, and low-energy
electrons leave
Electron Transport
• Oxidative phosphorylation
– O2 is the final electron
acceptor for low-energy
electrons from last of the
carrier molecules
– NADH2  3 ATP
– FADH2  2 ATP
• Enzyme cytochrome
oxidase splits apart O2
molecules
– Combines each O atom with 2
H+’s to make water
Animal Physiology, Hill et al., 2004
Resources
• Thermoregulation, Temperature & Radiation
• Metabolism, Energy Balance & Temperature Regulation