Chapter 25

Copyright © John Wiley & Sons, Inc. All rights reserved.
Chapter 25
Metabolism and
Nutrition

Metabolism and Nutrition
Metabolic reactions contribute to homeostasis by
harvesting chemical energy from consumed nutrients to
contribute to the body’s growth, repair, and normal
functioning

Metabolism denotes the sum of all body chemical
reactions
 Catabolism is breaking down larger molecules into smaller
molecules. Catabolic reactions provide more energy than
they consume; they are exergonic – they liberate heat
 Anabolism is building up smaller molecules into larger
molecules. Anabolic reactions consume more energy than
they produce; they are endergonic – they consume heat

Metabolism is an energy-balancing act between
catabolic reactions and anabolic reactions
 The molecule that participates most often in energy
exchanges in living cells is ATP (adenosine triphosphate),
which couples energy-releasing catabolic reactions to
energy-requiring anabolic reactions
◦ The exact reactions that occur depend on which
enzymes are active in a particular cell at a particular
time

A nutrient is a “food or liquid that supplies the body’s
metabolic needs. Nutrients include:
 A necessary chemical (such as Na+
and other minerals)
 A substance that provides energy (such as lipids or
carbohydrates like glucose)
 Something that helps in growth of new body
components (such as vitamins)
 A substance that repairs or maintains body functions
(such as proteins, or amino acids to make proteins)

ATP
Catabolic reactions transfer energy into the “high-
energy” phosphate bonds
of ATP, where it can
be released quickly
and easily
It is necessary to
have an understanding of the mechanisms of
generating ATP, and the nature of energy transfer
using oxidation [O] – reduction [H] reactions

ATP
ATP temporarily stores and transfers energy given off in catabolic
reactions and transfers it to anabolic reactions that require energy.

REDOX Reactions
Chemical reactions in which a pair of electrons are
exchanged as a means of transferring energy are called
REDOX reactions
 Oxidation is the removal of electrons
 Reduction is the addition of electrons
Remember:
OIL RIG

REDOX Reactions
Mainly we will be looking at the oxidation of glucose by
“burning it” in cells through a series of electron transfers
to ultimately yield water, carbon dioxide, and ATP
Oxidation of glucose leaves the product with a decrease
in potential energy

REDOX Reactions
Many steps in burning glucose require oxidation via a
dehydrogenation (REDOX ) reaction
 The liberated electron pair are lost along with an
hydrogen atom – this is called a
hydride ion, and is represented along
with it’s electron pair (H:-)
◦ if it is represented without the
electron pair [H], the electrons
and the negative charge are implied

REDOX Reactions
Instead of transferring electrons directly to ADP to make
ATP, they are often transferred to intermediate
coenzymes like nicotinamide
adenine dinucleotide
(NAD) and flavin
adenine dinucleotide
(FAD) – both are
B vitamins
NAD+ reduced by an electron pair to NADH

REDOX Reactions
Since oxidation-reduction reactions always occur
together, the oxidation of glucose results in reduction
of the coenzymes NAD +
and FAD+
as the electrons
from the H:-
ion are transferred to them
 Reduction, then, results in an
increase in potential energy;
energy taken from the
oxidized substrate (glucose in
our example)

Carbohydrate Metabolism
Glucose is not just an example we happen to choose – it is
indeed the body’s preferred source of fuel
 During digestion, polysaccharides and
disaccharides are hydrolyzed into the
monosaccharides glucose (80%),
fructose, and galactose
 These three monosaccharides are absorbed into the
villi of the small intestine and carried to the liver
◦ hepatocytes convert galactose and fructose to glucose

Carbohydrate Metabolism
The oxidation of glucose to form ATP...
Glucose (C6H12O6) + O2 CO2 + H2O + ATP
... is known as “Cellular Respiration” and occurs in 4 steps

Cellular Respiration
The 1st step in cellular respiration is to oxidize one 6-
carbon molecule of glucose into two 3-carbon
molecules of pyruvate (pyruvic
acid) in a series of steps
called glycolysis

Once glucose is transported into the cell via facilitated
diffusion (in the presence of insulin), it is combined with
a phosphate molecule (phosphorylation)
 Glucose-6-phosphate is different from glucose, so it
does not affect the concentration gradient for
transport of more glucose into the cell
Another phosphate group is then added to form glucose-
1, 6-diphosphate. Each phosphate group requires 1 ATP
worth of energy in order to be added to the glucose

Next, some oxidation occurs (finally!), and some
energy is recouped as the 6-
carbon glucose 1,6, diphosphate
is broken down to pyruvate
(producing 2 net ATP and 2
reduced molecules of NAD
(NADH)
 Glycolysis occurs solely in
the cytoplasm of the cell

The 2nd step in cellular respiration occurs as the result of
a choice – the choice is depends on the availability of
enough oxygen!
 If sufficient oxygen is
present in the cell acetyl-CoA
will be formed and cellular
respiration continues; if not,
lactic acid is formed and the “debt” will need to be
repaid at some future time
Pyruvic Acid Either
Or

The “Choice”
If oxygen is plentiful, the formation of acetyl-CoA is a
transition step to prepare carbon
fragments to enter the Krebs cycle
(the 3rd step in cellular respiration)
Two 2-carbon molecules of
acetyl-CoA are formed from the oxidation of two 3-
carbon molecules of pyruvic acid molecules
◦As 2 molecules of CO2 are given off, energy is
produced (and stored) as 2 molecules NADH
Pyruvic Acid Either
Or

To begin the Krebs cycle, acetyl-CoA diffuses into the
matrix of the mitochondria where the
2-carbon fragments are “dropped off” –
the CoA is now free to diffuse back
into the cytoplasm and “reload”
 With each turn of the cycle,
a 2-carbon acetyl fragment
is completely oxidized
yielding ATP, FADH2, and NADH

The 4th step in cellular respiration - the electron
transport chain – (ETC) is a system for extracting the
energy stored in the reduced coenzymes formed in the
previous steps
 The ETC is composed of a series of
electron carriers (integral membrane
proteins) embedded
within the inner
membrane
of the mitochondrium

As shown in this photomicrograph, the inner
mitochondrial membrane is folded into cristae that
increase its surface area, accommodating thousands
of copies of
electron transport
chain proteins
in each
mitochondrion

Transferred electrons are passed like a hot potato, from
a high energy level to a lower energy level
 Each electron carrier
is first reduced (picks
up electrons), before
giving up electrons
and becoming
re-oxidized

These transfer proteins are known as the cytochromes
of the electron transport chain – their purpose is to
siphon-off the energy
contained in the
reduced cofactors
(NADH and
FADH2)

Using the energy gained in the “hot potato toss”, the
cytochromes pump H+
ions into the inner mitochondrial
space. The high numbers of protons put into the inner-
mitochondrial space
become a reservoir of
potential energy – setting
up both a concentration
gradient and an
electrical gradient

Driven by this electrochemical gradient (also called
the proton motive force), the H+
ions flow back across
the membrane. The channels through which the H+
ions flow (also embedded
in the inner mitochondrial
membrane) are tied to
an ATP synthase that
generates ATP from
ADP and P

In the final event, the last of the 3 cytochromes passes its
electrons to one-half of a molecule of O2
 O2 becomes
negatively charged
and picks up two H from
the surrounding medium
to form H2O (metabolic water –
about 200 ml/day); thus, oxygen
becomes the final electron acceptor

Other role players in cellular respiration include:
 Pantothenic acid (Vit. B5), a water-soluble vitamin
needed to form coenzyme-A
◦ Riboflavin and niacin (Vits. B2 and B3), are used as
structural components of NAD and FAD cofactors
 CO2 is produced by decarboxylation reactions in
glycolysis and the Krebs cycle
 Metabolic water is formed in the electron transport
chain

Summary of Cellular Respiration
In the total oxidation of 1 molecule of glucose, 36-38
molecules of ATPs are generated, depending on the tissue
 Only 4 ATP are generated by substrate level
phosphorylation (directly transferring a high energy
phosphate from one organic molecule to another) in
glycolysis and the Krebs cycle
 Most of the ATP (either 32 or 34) is made by oxidative
phosphorylation using the cytochromes of the electron
transport chain and O2 as the final electron acceptor

Summary of Cellular Respiration
The location of events of cellular respiration
are summarized in this graphic
 Glycolysis is occurring in the
cytoplasm
 The Krebs cycle takes place in
the mitochondrial matrix
 The cytochrome proteins of the
electron transport chain are embedded
into the inner mitochondrial membrane

1
NADH + 2 H+
GLYCOLYSIS
2
2
2 Pyruvic acid
1 Glucose
ATP
1
NADH + 2 H+
GLYCOLYSIS
+ 2 H+NADH
CO2
FORMATION
OF ACETYL
COENZYME A
2
2
2
2
2 Acetyl
coenzyme A
2 Pyruvic acid
1 Glucose
ATP
2
1
NADH + 2 H+
GLYCOLYSIS
+ 2 H+NADH
CO2
FORMATION
OF ACETYL
COENZYME A
KREBS
CYCLE
+ 6 H+
CO2
FADH2
NADH
2
4
6
2
2
2
2
2
2 Acetyl
coenzyme A
2 Pyruvic acid
1 Glucose
ATP
ATP
2
3
1
NADH + 2 H+
GLYCOLYSIS
+ 2 H+NADH
CO2
FORMATION
OF ACETYL
COENZYME A
KREBS
CYCLE
+ 6 H+
CO2
FADH2
NADH
2
4
6
2
ELECTRON
TRANSPORT
CHAIN
e–
e–
e–
32 or 34
O26
6
2
2
2
2
H2O
Electrons
2 Acetyl
coenzyme A
2 Pyruvic acid
1 Glucose
ATP
ATP ATP
2
3
4

Glucose Storage and Release
If glucose is not needed immediately for ATP
production, it combines with many other molecules of
glucose to form glycogen, a polysaccharide that is the
only stored form of carbohydrate in our bodies
 This process is called glycogenesis,
and the body can store about
500 g of it (75% in
skeletal muscle fibers and the
rest in liver cells)

Glycogenolysis is the opposite of glycogenesis: When
body activities require ATP, stored glycogen is broken
down into glucose and released into the blood to be
transported to cells,
where it will be
catabolized by
the processes of
cellular respiration
already described
Glucose Storage and Release

Making Glucose
Gluconeogenesis is the process of forming “new”
glucose or its metabolites from fat or protein (from
non-carbohydrate sources). Gluconeogenesis is always
taking place, but it occurs on a large scale during
fasting, starving, or eating a low carbohydrate diet
 Lactic acid, amino acids, and the
glycerol portion of triglycerides
are used to form glucose
molecules or pyruvic acid
to enter the Krebs cycle

Lipids
Although the word “fat” is commonly used to mean
lipids, fats are, in fact, just one subgroup of lipids called
triglycerides
 Other lipids include waxes, sterols (steroid hormones),
fat-soluble vitamins (such as vitamins A, D, E and K),
monoglycerides, diglycerides, phospholipids, and
others
◦ For metabolic purposes, triglycerides are a
condensed form of useable energy

Lipids
All triglycerides are composed of a glycerol backbone
combined with 3 fatty acids
 Fatty acids are anywhere
from 4 to 24 carbons long,
and they may have all
single carbon-carbon
bonds (saturated), or
some double or triple
bonds (making them unsaturated)

Lipids
Triglycerides are nonpolar, and therefore very
hydrophobic molecules
 To be transported in watery blood, they must first be
made more water-soluble by combining them with
carrier molecules called lipoproteins (produced in
the liver)
◦ Lipoproteins vary in their size, density, and the
amount of cholesterol and protein in their make-
up

Lipoproteins
In general, however, all lipoproteins have:
 An outer shell that is made hydrophilic due to polar
proteins (plus amphipathic
phospholipid and
cholesterol)
 An inner core that is
hydrophobic - a place
where the triglycerides
are transported

Lipid Metabolism
The term lipogenesis means fat synthesis, while
lipolysis refers to the oxidation (catabolism) of lipids to
yield glucose (which then yields ATP)
 If the body has no
immediate needs,
lipids are stored
in adipose
tissue

Lipid Metabolism
Lipolysis begins with separating the glycerol backbone
of triglycerides from the 3 fatty acids
 Beta oxidation is the process of
cleaving off 2-carbon fragments
from long fatty acid chains
◦The 2-carbon acetyl groups
are joined to coenzyme A to
form acetyl CoA for insertion
into Krebs cycle

Lipid Metabolism
The oxidation of triglycerides (specifically, the 3 carbon
glycerol backbone), results in the formation of ketoacids,
(ketone bodies) which must be eliminated by the kidneys
in order to maintain homeostasis
 Ketogenesis is a normal part of fat breakdown, but an
excess will cause a metabolic acidosis
◦ A mild ketoacidosis can occur even with a short 24
hour fast, and is responsible for the headaches and
some of the other symptoms that are part of fasting

Protein Metabolism
Proteins are not a primary source of energy; and unlike
lipids and sugars, proteins are not stored
 Yet a certain amount of protein catabolism occurs in
the body each day as proteins from worn-out cells
are broken down into amino acids
◦ Some amino acids are converted into other amino
acids, peptide bonds are re-formed, and new
proteins are synthesized as part of the recycling
process

Protein Metabolism
In protein synthesis, transamination refers to the transfer
of an amino group (NH2) to pyruvic acid or another acid
in the Krebs cycle to form an amino acid
In protein catabolism, deamination refers to the removal
of an amino group leaving the carbons of a carboxylic
acid to be used to make ATP
 Essential amino acids are the 10 amino acids that can’t be
synthesized by the body
 Non-essential amino acids are the others that can be
synthesized by the body

Three pivotal molecules stand at the crossroads of many
of the chemical reactions in carbohydrate, lipid, and
protein metabolism: acetyl-CoA, glucose-6-phosphate,
and pyruvic acid
occupy these key
entry points into,
and out of the
Krebs cycle
Metabolic Crossroads

1
C
CH2
COOH
O
Oxaloacetic acid
COOH
Citric acid
H2C COOH
COOHHOC
H2C COOH
+ H+
Pyruvic
acid
Acetyl
coenzyme A
C
CH3
O
CH3
C
COOH
O
To electron
transport chain
H2O
CO2
NAD+
KREBS
CYCLE
NADH
CoA
CoA
1
C
CH2
COOH
O
Oxaloacetic acid
COOH
Isocitric acid
H2C COOH
HOC COOH
HC COOH
H
Citric acid
H2C COOH
COOHHOC
H2C COOH
+ H+
Pyruvic
acid
Acetyl
coenzyme A
C
CH3
O
CH3
C
COOH
O
To electron
transport chain
H2O
CO2
NAD+
KREBS
CYCLE
NADH
CoA
CoA
2
1
To electron
transport chain
CO2
+ H+
C
CH2
COOH
O
Oxaloacetic acid
COOH
Alpha-ketoglutaric acid
H2C COOH
HCH
C COOH
Isocitric acid
H2C COOH
HOC COOH
HC COOH
H
Citric acid
H2C COOH
COOHHOC
H2C COOH
NAD+
+ H+
Pyruvic
acid
Acetyl
coenzyme A
C
CH3
O
CH3
C
COOH
O
To electron
transport chain
H2O
CO2
NAD+
KREBS
CYCLE
NADH
NADH
CoA
CoA
2
3
O
1
To electron
transport chain
CO2
+ H+NADH
CO2
+ H+
C
CH2
COOH
O
Oxaloacetic acid
COOH
Succinyl CoA
H2C COOH
CH2
C S CoA Alpha-ketoglutaric acid
H2C COOH
HCH
C COOH
Isocitric acid
H2C COOH
HOC COOH
HC COOH
H
Citric acid
H2C COOH
COOHHOC
H2C COOH
NAD+
NAD+
+ H+
Pyruvic
acid
Acetyl
coenzyme A
C
CH3
O
CH3
C
COOH
O
To electron
transport chain
H2O
CO2
NAD+
KREBS
CYCLE
NADH
NADH
O
CoA
O
CoA
2
3
4
1
To electron
transport chain
CO2
+ H+NADH
CO2
+ H+
C
CH2
COOH
O
Oxaloacetic acid
COOH
H2C COOH
H2C COOH
Succinic acid
Succinyl CoA
H2C COOH
CH2
H2C COOH
HCH
C COOH
Isocitric acid
H2C COOH
HOC COOH
HC COOH
H
Citric acid
H2C COOH
COOHHOC
H2C COOH
NAD+
NAD+
GDP
+ H+
Pyruvic
acid
Acetyl
coenzyme A
C
CH3
O
CH3
C
COOH
O
To electron
transport chain
ADP
H2O
CO2
NAD+
KREBS
CYCLE
NADH
NADH
ATP
GTP
O
CoA
CoA
O
CoA
2
3
4
5
1
To electron
transport chain
CO2
+ H+NADH
CO2
+ H+
To electron
transport
chain
C
CH2
COOH
O
Oxaloacetic acid
COOH
H2C COOH
H2C COOH
Succinic acid
Succinyl CoA
H2C COOH
CH2
H2C COOH
HCH
C COOH
Isocitric acid
H2C COOH
HOC COOH
HC COOH
H
Citric acid
H2C COOH
COOHHOC
H2C COOH
Fumaric acid
NAD+
NAD+
GDP
FAD
HC
CH
+ H+
Pyruvic
acid
Acetyl
coenzyme A
C
CH3
O
CH3
C
COOH
O
To electron
transport chain
ADP
FADH2
COOH
COOH
H2O
CO2
NAD+
KREBS
CYCLE
NADH
NADH
ATP
GTP
CoA
CoA
O
CoA
2
3
4
5
6
O
1
To electron
transport chain
CO2
+ H+NADH
CO2
+ H+
To electron
transport
chain
C
CH2
COOH
O
Oxaloacetic acid
COOH
HCOH
CH2
COOH
COOH
H2C COOH
H2C COOH
Succinic acid
Malic acid
Succinyl CoA
H2C COOH
CH2
H2C COOH
HCH
C COOH
Isocitric acid
H2C COOH
HOC COOH
HC COOH
H
Citric acid
H2C COOH
COOHHOC
H2C COOH
Fumaric acid
NAD+
NAD+
GDP
FAD
HC
CH
+ H+
Pyruvic
acid
Acetyl
coenzyme A
C
CH3
O
CH3
C
COOH
O
To electron
transport chain
ADP
FADH2
COOH
COOH
H2O
H2O
CO2
NAD+
KREBS
CYCLE
NADH
NADH
ATP
GTP
CoA
CoA
O
CoA
2
3
4
5
6
7
O
1
To electron
transport chain
CO2
+ H+NADH
CO2
+ H+
To electron
transport
chain
C
CH2
COOH
O
Oxaloacetic acid
COOH
+ H+NADH
HCOH
CH2
COOH
COOH
H2C COOH
H2C COOH
Succinic acid
Malic acid
Succinyl CoA
H2C COOH
CH2
H2C COOH
HCH
C COOH
Isocitric acid
H2C COOH
HOC COOH
HC COOH
H
Citric acid
H2C COOH
COOHHOC
H2C COOH
Fumaric acid
NAD+
NAD+
GDP
FAD
NAD+
HC
CH
+ H+
Pyruvic
acid
Acetyl
coenzyme A
C
CH3
O
CH3
C
COOH
O
To electron
transport chain
ADP
FADH2
COOH
COOH
H2O
H2O
CO2
NAD+
KREBS
CYCLE
NADH
NADH
ATP
GTP
CoA
CoA
O
CoA
2
3
4
5
6
7
8
O
Krebs Cycle Reactions

Metabolic Adaptations
During the absorptive state ingested nutrients enter the
blood stream and glucose is readily available
During the postabsorptive state absorption of nutrients
from GI tract is complete and energy needs must be met
by fuels in the body
 Maintaining a steady blood glucose is critical because
the nervous system and red blood cells depend solely
on glucose as an energy source
◦ The effects of insulin dominate

The Absorptive State
Soon after a meal glucose, amino acids, and lipid
nutrients enter the blood. Triglycerides enter the blood
carried in large lipoproteins called chylomicrons. There
are 2 metabolic hallmarks of this state:
 Glucose is oxidized to produce ATP in all body cells
 Any excess fuel molecules are stored in hepatocytes,
adipocytes, and skeletal muscle cells
Pancreatic beta cells begin to release insulin to promote
entry of glucose and amino acids into cells

The Absorptive State
During the absorptive state, most body cells are
concerned with
producing ATP
by oxidizing
glucose

AMINO ACIDS GLUCOSE TRIGLYCERIDES
(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINAL
TRACT
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
1
(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINAL
TRACT
HEPATOCYTES IN LIVER
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Fatty acids
Triglycerides
Glyceraldehyde
3-phosphate Glycogen
Glucose
+ H2O +CO2 ATP
1
2
(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINAL
TRACT
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fatty acids
Triglycerides
Glyceraldehyde
Glucose
+ H2O +CO2 ATP
1
2
3
(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINAL
TRACT
GLUCOSE
SKELETAL
MUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Fatty
acids
Triglycerides
Glyceraldehyde
3-phosphate
Glucose
Fatty acids
Triglycerides
Glyceraldehyde
Glucose
GlycogenGlycogen
+ H2O +CO2 ATP
1
2
3
4
4
(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINAL
TRACT
GLUCOSE
SKELETAL
MUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fatty
acids
Triglycerides
Glyceraldehyde
3-phosphate
Glucose
Fatty acids
Triglycerides
Glyceraldehyde
Glucose
GlycogenGlycogen
+ H2O +CO2 ATP
1
2
3
4 5
4
(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINAL
TRACT
GLUCOSE
SKELETAL
MUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fatty
acids
Triglycerides
Glyceraldehyde
3-phosphate
Glucose
Keto acids
Fatty acids
Triglycerides
Glyceraldehyde
Glucose
GlycogenGlycogen
+ H2O +CO2 ATP
1
2
3
4 5
6
4
(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINAL
TRACT
GLUCOSE
SKELETAL
MUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fatty
acids
Triglycerides
Glyceraldehyde
3-phosphate
Glucose
Keto acids
Fatty acidsProteins
Triglycerides
Glyceraldehyde
Glucose
GlycogenGlycogen
+ H2O +CO2 ATP
1
2
3
4 5
6
7
4
(in chylomicrons)
Blood
GLUCOSE
GASTROINTESTINAL
TRACT
GLUCOSE
SKELETAL
MUSCLE
Storage
+ H2O +CO2
MOST TISSUES
Oxidation
ATP
Triglycerides
ADIPOSE TISSUE
VLDLs
Triglycerides
Fatty
acids
Triglycerides
Glyceraldehyde
3-phosphate
Glucose
Keto acids
Fatty acidsProteins
Triglycerides
Glyceraldehyde
Glucose
GlycogenGlycogen
ProteinsProteins
+ H2O +CO2 ATP
1
2
3
4 5
6
7
8
4

The Postabsorptive State
About 4 hours after the last meal absorption in the small
intestine is nearly complete and blood glucose levels start to
fall. The main metabolic challenge at this point is to
maintain normal blood glucose levels
 As blood glucose levels decline, insulin secretion falls and
glucagon secretion increases
◦ Blood glucose levels are sustained by the breakdown of
liver glycogen, lipolysis, and gluconeogenesis using
lactic acid and/or amino acids

The Postabsorptive State
The process is supported by sympathetic nerve endings
that release norepinephrine, and by the adrenal medulla
that releases epinephrine and norepinephrine directly
into the
blood

1
Liver glycogen
Glucose
LIVER
Blood
HEARTADIPOSE TISSUE
SKELETAL MUSCLE TISSUE
OTHER TISSUES
1
Liver glycogen
Glucose
LIVER
Glycerol
Blood
HEART
Fatty acidsGlycerol
Triglycerides
ADIPOSE TISSUE
OTHER TISSUES
2
Fatty acids
1
Liver glycogen
Glucose
LIVER
Lactic acid
Glycerol
Blood
HEART
Fatty acidsGlycerol
Triglycerides
ADIPOSE TISSUE
OTHER TISSUES
3
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Lactic acid
Glycerol
Blood
HEART
Muscle proteins
Fatty acidsGlycerol
Triglycerides
ADIPOSE TISSUE
Fasting or
starvation
OTHER TISSUES
ProteinsAmino acids
Amino acids
4
4
3
4
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Lactic acid
Glycerol
Blood
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
Triglycerides
ADIPOSE TISSUE
Fasting or
starvation
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Amino acids
Fatty acids
ATP
ATP
ATP
4
5
5
4
3
5
4
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Lactic acid
Glycerol
Blood
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
Triglycerides
ADIPOSE TISSUE
Fasting or
starvation
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Amino acids
Fatty acids
Lactic acid
ATP
ATP
ATP
ATP
4
5
5
6
4
3
5
4
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Lactic acid
Glycerol
Blood
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
Triglycerides
ADIPOSE TISSUE
Fasting or
starvation
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Amino acids
Fatty acids
Lactic acid
ATP
ATP
ATP
ATP
ATP
4
5
5
6
7
4
3
5
4
2
Fatty acids
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Fatty acids
Lactic acid
Ketone bodies
Glycerol
Blood
NERVOUS
TISSUE Ketone
bodies
Glucose
Starvation
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
Triglycerides
ADIPOSE TISSUE
Fasting or
starvation
Ketone bodies
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Amino acids
Fatty acids
Ketone bodies
Lactic acid
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP ATP
4
5
8
5
6
8
8
7
4
3
5
4
2
8
1
Liver glycogen
Keto acids
Glucose
Amino acids
LIVER
Fatty acids
Lactic acid
Ketone bodies
Glycerol
Blood
NERVOUS
TISSUE Ketone
bodies
Glucose
Starvation
HEART
Fatty acids
Muscle proteins
Fatty acidsGlycerol
Triglycerides
ADIPOSE TISSUE
Fasting or
starvation
Ketone bodies
OTHER TISSUES
Fatty acids
ProteinsAmino acids
Glucose
6-phosphate
Pyruvic acid
Lactic
acid
Muscle glycogen
(aerobic) (anaerobic)
Amino acids
Fatty acids
Ketone bodies
Lactic acid
ATP
O2
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP
ATP ATP
+ O2–
4
5
8
5
6
8
8
7
4
3
9
5
4
2
8

Basal Metabolic Rate
The metabolic rate is the overall rate at which metabolic
reactions use energy. Basal metabolic rate (BMR) is
measured with the body in a quiet, fasting condition
 Whatever the metabolic rate (other than death!), heat
is a constant by-product of metabolic reactions, and
can be expressed in calories
 The BMR is 1200–1800 Cal/day in adults, or about 24
Cal/kg of body mass in adult males and 22 Cal/kg in
adult females

Body Temperature
Despite wide fluctuations in environmental
temperatures, homeostatic mechanisms maintain a
normal range for internal (core) body temperature at
37°C (98.6°F)
 Peripheral tissues can be much cooler (“shell
temperature 1-6°C lower)
◦ Body temperature is maintained by hormonal
regulation of the BMR, exercise, and sympathetic
nervous system stimulation

Heat and Energy Balance
Heat loss occurs through:
 Conduction to solid materials in contact with the body,
e.g. walking barefoot on the floor
 Convection is the transfer of heat when a gas or liquid
flows over an object, e.g. using a fan on a hot day
 Thermal radiation is the transfer of heat in the form of
electromagnetic energy (infrared, and encompassing
visible light) between two bodies not in contact
 Evaporation occurs when converting a liquid to a gas

The Hypothalamic Thermostat
The control center that functions as the body’s
thermostat is a group of neurons in the anterior part
(preoptic area) of the hypothalamus that receives
impulses from thermoreceptors scattered throughout
the body
 Neurons of the preoptic area generate nerve impulses
at a higher frequency when blood temperature
increases, and at a lower frequency when blood
temperature decreases

Thermoregulation
If the core temperature declines,
skin blood vessels constrict and
thyroid hormones and
catecholamines (epinephrine and
norepinephrine) are released.
Cellular metabolism increases and
shivering my ensue
If core body temperature rises,
blood vessels of the skin dilate,
sweat glands are stimulated, and
the metabolic rate is lowered

Nutrition
Nutrients are chemical substances in food that body cells
use for growth, maintenance, and repair
 There are 6 main types of nutrients
◦ water , which is needed in the largest amount
◦ carbohydrates
◦ lipids
◦ proteins
◦ minerals
◦ vitamins

Nutrition
Guidelines for nutritious eating are not known with
certainty. Different populations around the world eat
radically different amounts and types of carbohydrates,
fats and protein in their diets. Basic guidelines include:
 Eat a variety of foods
 Maintain a healthy weight
 Choose foods low in fat, saturated fat and cholesterol
 Eat plenty of vegetables, fruits and grain products
 Use sugars in moderation only

Nutrition
In this nutrition pyramid the six color bands represent the
five basic food groups plus oils. Foods from all bands are
needed each day

Nutrition
Essential minerals are those inorganic elements that
occur naturally in the earth’s crust and are needed to
maintain life. The major role of minerals is to help
regulate enzymatic reactions and build bone
 Recommendations are to eat foods that contain
enough calcium, phosphorus, iron and iodine
◦ Excess amounts of most minerals are excreted in
urine and feces

Nutrition
Vitamins are organic nutrients required in small amounts
to maintain growth and normal metabolism - they do not
provide energy or serve as the body’s building materials
 Most cannot be synthesized by us, and no single food
contains all the required vitamins
 They are divided into those that are water soluble
(several B vitamins and vitamin C), and those that are
fat soluble (A, D, E, K)
◦ Most vitamins serve as coenzymes

Vitamin Deficiencies
Vitamin A is needed to make the visual pigment retinal
 Deficiency leads to night blindness and a weakened
immune system
Vitamin D is needed for calcium absorption
 Deficiency results in impaired bone mineralization,
and leads to bone softening diseasess such as rickets
in children and osteomalacia in adults

Vitamin K is needed to make clotting factors II, VII,
and IX, X
 A deficiency such as due to long-term antibiotic
therapy or taking anticoagulant medications leads to
delayed clotting times
Vitamin C is necessary for proper growth of connective
tissues like collagen
 Deficiency manifests as a disease called Scurvy

Niacin (B3) is a precursor to NAD (NADH), which plays
essential metabolic roles in living cells
 A deficiency (which is called Pellagra) results from an
all corn diet, and manifests as dermatitis, diarrhea, and
dementia
Thiamine (B1) is essential for neural function and
carbohydrate metabolism
 A deficiency (called Beriberi) results from a polished
rice diet, and manifests with muscle wasting, and
impaired reflexes

Folic Acid (vitamin B9) is needed to synthesize the bases
used to replicate DNA
 A deficiency manifests as a macrocytic anemia
without nerve involvement
Cyanocobalamin (B12 ) is important for normal nerve
function and for the formation of blood
 A deficiency manifests as pernicious anemia, ataxia,
memory loss, weakness, personality and mood changes

Obesity
Obesity is defined as a body weight 10-20% (or more)
above the desirable level because of excess fat
 An explanation for the prevalence of obesity in our
society is not universally agreed upon. In a complex
interplay, many psychosocial and physiological issues
appear to contribute
 Obesity puts an individual at risk for a large number
of diseases and conditions – cardiovascular disease
predominant

Obesity
Factors that are especially prevalent in western society
include:
 An abundance of good-tasting food
 Working longer hours (less time preparing good food)
 Fast-foods
 Super-size portions
 Sedentary jobs
 Lack of Exercise

Chapter 25

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Chapter 25