Download Nutrition, Metabolism, and Body Temperature Regulation

Nutrition,
Metabolism,
and Body
Temperature
Regulation
Nutrition
• Nutrient – a substance that
promotes normal growth,
maintenance, and repair
• Major nutrients – carbohydrates, lipids,
and proteins
• Other nutrients – vitamins and minerals
(and technically speaking, water)
Carbohydrates
• Complex carbohydrates (starches) are
found in bread, cereal, flour, pasta, nuts,
and potatoes
• Simple carbohydrates (sugars) are found
in soft drinks, candy, fruit, and ice cream
• Glucose is the molecule ultimately used by
body cells to make ATP
• Neurons and RBCs rely almost entirely
upon glucose to supply their energy needs
• Excess glucose is converted to glycogen
or fat and stored
Lipids
• The most abundant dietary lipids,
triglycerides, are found in both
animal and plant foods
• Essential fatty acids – linoleic and linolenic acid,
found in most vegetables, must be ingested
• Dietary fats:
– Help the body to absorb vitamins
– Are a major energy fuel of hepatocytes and skeletal
muscle
– Are a component of myelin sheaths and all cell
membranes
Proteins
• Proteins supply:
– Essential amino acids, the building
blocks for nonessential amino acids
– Nitrogen for nonprotein nitrogen-containing
substances
• Daily intake should be approximately
0.8g/kg of body weight
Vitamins
• Organic (carbon) compounds
needed for growth and good
health
• They are crucial in helping the body use
nutrients and often function as coenzymes
• Only vitamins D, K, and B are synthesized
in the body; all others must be ingested
• Water-soluble vitamins (B-complex and C)
are absorbed in the gastrointestinal tract
– B12 additionally requires gastric intrinsic factor
to be absorbed
Minerals
• Seven minerals are required
in moderate amounts
– Calcium, phosphorus, potassium, sulfur,
sodium, chloride, and magnesium
• Dozens are required in trace amounts
• Minerals work with nutrients to ensure
proper body functioning
• Calcium, phosphorus, and magnesium
salts harden bone
Minerals
• Sodium and chloride help
maintain normal osmolarity,
water balance, and are essential in nerve
and muscle function
• Uptake and excretion must be balanced to
prevent toxic overload
Metabolism
• Metabolism – all chemical reactions
necessary to maintain life
• Cellular respiration – food fuels are broken
down within cells and some of the energy
is captured to produce ATP
– Anabolic reactions – synthesis of larger
molecules from smaller ones
– Catabolic reactions – hydrolysis of complex
structures into simpler ones
Metabolism
• Enzymes shift the high-energy phosphate
groups of ATP to other molecules
• These phosphorylated molecules are
activated to perform cellular functions
Stages of Metabolism
•
Energy-containing nutrients are
processed in three major stages
1. Digestion – breakdown of food; nutrients are
transported to tissues
2. Anabolism and formation of catabolic intermediates
where nutrients are:
1. Built into lipids, proteins, and glycogen
2. Broken down by catabolic pathways to pyruvic acid and
acetyl CoA
3. Oxidative breakdown – nutrients are catabolized to
carbon dioxide, water, and ATP
Stages of
Metabolism
Carbohydrate Metabolism
•
Since all carbohydrates are transformed
into glucose, it is essentially glucose
metabolism
• Oxidation of glucose is shown by the
overall reaction:
C6H12O6 + 6O2  6H2O + 6CO2 + 36 ATP +
heat
• Glucose is catabolized in three pathways
1. Glycolysis
2. Krebs cycle
3. The electron transport chain and oxidative
phosphorylation
Carbohydrate Catabolism
Glycolysis
•
A three-phase pathway in which:
1. Glucose is oxidized into pyruvic acid
2. NAD+ is reduced to NADH + H+
3. ATP is synthesized by substrate-level
phosphorylation
•
Pyruvic acid:
– Moves on to the Krebs cycle in an aerobic
pathway (with O2)
– Is reduced to lactic acid in an anaerobic
environment (if no O2)
3 Outcomes of Glycolysis
3. ATP is
synthesized by
substrate-level
phosphorylation
2. NAD+ is reduced
to NADH + H+
1. Glucose is
oxidized
into pyruvic
acid
Glycolysis: Phase 1 and 2
• Phase 1: Sugar activation
– Two ATP molecules activate glucose into
fructose-1,6-diphosphate
• Phase 2: Sugar cleavage
– Fructose-1,6-bisphosphate is cleaved into two
3-carbon isomers
• Bishydroxyacetone phosphate
• Glyceraldehyde 3-phosphate
Glycolysis: Phase 3
• Phase 3: Oxidation and ATP formation
– The 3-carbon sugars are oxidized (reducing
NAD+)
– Inorganic phosphate groups (Pi) are attached
to each oxidized fragment
– The terminal phosphates are cleaved and
captured by ADP to form four ATP molecules
Glycolysis: Phase 3
•
The final products are:
1. Two pyruvic acid molecules
2. Two NADH + H+ molecules (reduced NAD+)
3. A net gain of two ATP molecules
Krebs Cycle: Preparatory Step
• Occurs in the mitochondrial matrix and is
fueled by pyruvic acid and fatty acids
Krebs Cycle: Preparatory Step
•
Pyruvic acid is converted to acetyl CoA in three
main steps:
1. Decarboxylation
•
•
Carbon is removed
Carbon dioxide is released
2. Oxidation
•
•
Hydrogen atoms are removed from pyruvic acid
NAD+ is reduced to NADH + H+
3. Formation of acetyl CoA – the resulting acetic acid is
combined with coenzyme A, a sulfur-containing
coenzyme, to form acetyl CoA
Krebs Cycle
•
An eight-step cycle in which each acetic
acid is decarboxylated and oxidized,
generating:
1.
2.
3.
4.
•
Three molecules of NADH + H+
One molecule of FADH2
Two molecules of CO2
One molecule of ATP
For each molecule of glucose entering
glycolysis, two molecules of acetyl CoA
enter the Krebs cycle
Krebs Cycle
Electron Transport Chain
•
Food (glucose) is oxidized and the released
hydrogens:
1. Are transported by coenzymes NADH and
FADH2
2. Enter a chain of proteins bound to metal
atoms (cofactors)
3. Combine with molecular oxygen to form
water
4. Release energy
• The energy released is harnessed to attach
inorganic phosphate groups (Pi) to ADP,
making ATP by oxidative phosphorylation
Mechanism of Oxidative
Phosphorylation
• The hydrogens delivered to the chain are
split into protons (H+) and electrons
– The protons are pumped across the inner
mitochondrial membrane by:
• NADH dehydrogenase (FMN, Fe-S)
• Cytochrome b-c1
• Cytochrome oxidase (a-a3)
– The electrons are shuttled from one acceptor
to the next
Mechanism of Oxidative
Phosphorylation
1. Electrons are delivered to oxygen,
forming oxygen ions
2. Oxygen ions attract H+ to form water
3. H+ pumped to the intermembrane space:
– Diffuses back to the matrix via ATP
synthase
– Releases energy to make ATP
Mechanism of Oxidative
Phosphorylation
1. Hydrogens are
split into protons
and electrons
Mechanism of Oxidative
Phosphorylation
2. Protons are shuttled across membrane
Mechanism of Oxidative
Phosphorylation
3. Electrons cross
membrane as well but fall
back sooner
Mechanism of Oxidative
Phosphorylation
4. When electrons fall back, you have
2 gradients, a pH gradient and a
strong charge gradient
Mechanism of Oxidative
Phosphorylation
5. When H comes back, it can give
off energy that is used to make ATP
Summary of ATP Production
Lipid Metabolism
• Most products of fat metabolism are
transported in lymph as chylomicrons
• Lipids in chylomicrons are hydrolyzed by
plasma enzymes and absorbed by cells
• Catabolism of fats involves two separate
pathways
Glycerol
Fatty Acids
– Glycerol pathway
– Fatty acids pathway
Lipid
Metabolism
Lipogenesis and Lipolysis
• Excess dietary glycerol and fatty acids
undergo lipogenesis to form triglycerides
• Glucose is easily converted into fat since
acetyl CoA is:
– An intermediate in glucose catabolism
– The starting molecule for the synthesis of fatty
acids
Lipogenesis and Lipolysis
• Lipolysis, the breakdown of stored fat, is
essentially lipogenesis in reverse
• Oxaloacetic acid is necessary for the
complete oxidation of fat
– Without it, acetyl CoA is converted into
ketones (ketogenesis)
Lipogenesis and Lipolysis
The main point here is that lipids and sugars are interconvertible
Protein Metabolism
• Excess dietary protein results in amino
acids being:
– Oxidized for energy
– Converted into fat for storage
• Amino acids must be deaminated prior to
oxidation for energy
Protein Metabolism
Synthesis of Proteins
• Amino acids are the most important
anabolic nutrients, and they form:
– All protein structures
– The bulk of the body’s functional molecules
State of the Body
• The body exists in a dynamic catabolicanabolic state
• Organic molecules (except DNA) are
continuously broken down and rebuilt
• The body’s total supply of nutrients
constitutes its nutrient pool
Absoprtive and Postabsorptive
States
• Metabolic controls equalize blood
concentrations of nutrients between two
states
• Absorptive
– The time during and shortly after nutrient
intake
• Postabsorptive
– The time when the GI tract is empty
– Energy sources are supplied by the
breakdown of body reserves
Absorptive State (Full Stomach)
• The major metabolic thrust is anabolism
and energy storage
– Amino acids become proteins
– Glycerol and fatty acids are converted to
triglycerides
– Glucose is stored as glycogen
• Dietary glucose is the major energy fuel
• Excess amino acids are deaminated and
used for energy or stored as fat in the liver
Absorptive State
Principal Pathways of the
Absorptive State
• In muscle:
– Amino acids become protein
– Glucose is converted to glycogen
• In the liver:
– Amino acids become protein or are
deaminated to keto acids
– Glucose is stored as glycogen or converted to
fat
Principal Pathways of the
Absorptive State
• In adipose tissue:
– Glucose and fats are converted and stored as
fat
• All tissues use glucose to synthesize ATP
Principal Pathways of the
Absorptive State
Insulin Effects on Metabolism
• Insulin controls the absorptive state and its
secretion is stimulated by:
– Increased blood glucose
– Elevated amino acid levels in the blood
– Gastrin, CCK, and secretin
• Insulin enhances:
– Active transport of amino acids into tissue
cells
– Facilitated diffusion of glucose into tissue
Insulin
Effects on
Metabolism
Diabetes Mellitus
• A consequence of inadequate insulin
production (Type I) or abnormal insulin
receptors (Type II)
• Glucose becomes unavailable to most
body cells
• Metabolic acidosis, protein wasting, and
weight loss result as fats and tissue
proteins are used for energy
Postabsorptive State
• The major metabolic thrust is catabolism and
replacement of fuels in the blood
– Proteins are broken down to amino acids
– Triglycerides are turned into glycerol and fatty acids
– Glycogen becomes glucose
• Glucose is provided by glycogenolysis and
gluconeogenesis
• Fatty acids and ketones are the major energy
fuels
• Amino acids are converted to glucose in the liver
Postabsorptive State
Principle Pathways in the
Postabsorptive State
• In muscle:
– Protein is broken down to amino acids
– Glycogen is converted to ATP and pyruvic
acid (lactic acid in anaerobic states)
Principle Pathways in the
Postabsorptive State
• In the liver:
– Amino acids, pyruvic acid, stored glycogen,
and fat are converted into glucose
– Fat is converted into keto acids that are used
to make ATP
• Fatty acids (from adipose tissue) and
ketone bodies (from the liver) are used in
most tissue to make ATP
• Glucose from the liver is used by the
nervous system to generate ATP
Principle Pathways in the
Postabsorptive State
Hormonal and Neural Controls
of the Postabsorptive State
• Decreased plasma glucose concentration
and rising amino acid levels stimulate alpha
cells of the pancreas to secrete glucagon
(the antagonist of insulin)
• Glucagon stimulates:
– Glycogenolysis and gluconeogenesis
– Fat breakdown in adipose tissue
– Glucose sparing
Hormonal and Neural Controls
of the Postabsorptive State
• In response to low plasma glucose, the
sympathetic nervous system releases
epinephrine, which acts on the liver,
skeletal muscle, and adipose tissue to
mobilize fat and promote glycogenolysis
Cholesterol
• Is the structural basis of bile salts, steroid
hormones, and vitamin D
• Makes up part of the hedgehog molecule
that directs embryonic development
• Is transported to and from tissues via
lipoproteins
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
Lipoproteins
• High levels of HDL are thought to protect
against heart attack
• High levels of LDL, especially lipoprotein
(a), increase the risk of heart attack
Metabolic Rate
• Rate of energy output (expressed per
hour) equal to the total heat produced by:
– All the chemical reactions in the body
– The mechanical work of the body
• Measured directly with a calorimeter or
indirectly with a respirometer
Metabolic Rate
• Basal metabolic rate (BMR)
– Reflects the energy the body needs to
perform its most essential activities
• Total metabolic rate (TMR)
– Total rate of kilocalorie consumption to fuel all
ongoing activities
Factors that Influence BMR
• Surface area, age, gender, stress, and
hormones
• As the ratio of surface area to volume
increases, BMR increases
• Males have a disproportionately high BMR
• Stress increases BMR
• Thyroxine increases oxygen consumption,
cellular respiration, and BMR