Chapter 25

Copyright © John Wiley & Sons, Inc. All rights reserved.

Chapter 25Metabolism and

Nutrition


Metabolism and NutritionMetabolic reactions contribute to homeostasis

by harvesting chemical energy from

consumed nutrients to contribute to the

body’s growth, repair, and normal functioning


Metabolism and Nutrition

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 and Nutrition

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


Metabolism and NutritionA 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)


ATPCatabolic 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 ReactionsChemical 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

Remembe

r: 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 ReactionsMany 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 ReactionsInstead 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 MetabolismGlucose 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 MetabolismThe oxidation of glucose to form ATP...

Glucose (C6H12O6) + O2 CO2 + H2O +

ATP

... is known as “Cellular Respiration” and

occurs in 4 steps


Cellular RespirationThe 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


Cellular RespirationOnce 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


Cellular Respiration 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


Cellular RespirationThe 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

EitherO

r


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

Cellular Respiration


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



Cellular RespirationAs 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


Cellular RespirationTransferred 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


Cellular RespirationThese 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)


Cellular RespirationUsing 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


Cellular RespirationDriven 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



Cellular RespirationOther 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 RespirationThe 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


1NADH + 2 H+

GLYCOLYSIS2

2

2 Pyruvic acid

1 Glucose

ATP1

NADH + 2 H+

GLYCOLYSIS

+ 2 H+NADH

CO2FORMATIONOF ACETYLCOENZYME A

2

2

2

2

2 Acetylcoenzyme A

2 Pyruvic acid

1 Glucose

ATP

2

1NADH + 2 H+

GLYCOLYSIS

+ 2 H+NADH


KREBSCYCLE

+ 6 H+

CO2

FADH2

NADH

2

4

6

2

2

2

2

2

2 Acetylcoenzyme A

2 Pyruvic acid

1 Glucose

ATP

ATP

2

3

1NADH + 2 H+

GLYCOLYSIS

+ 2 H+NADH


KREBSCYCLE

+ 6 H+

CO2

FADH2

NADH

2

4

6

2

ELECTRONTRANSPORTCHAIN

e–

e–

e–

32 or 34

O26

6

2

2

2

2

H2O

Electrons

2 Acetylcoenzyme A

2 Pyruvic acid

1 Glucose

ATP

ATP ATP

2

3

4



Glucose Storage and ReleaseIf 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 GlucoseGluconeogenesis 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


LipidsAlthough 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


LipidsAll 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)


LipidsTriglycerides 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


LipoproteinsIn 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 MetabolismThe 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 MetabolismLipolysis 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 MetabolismThe 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 MetabolismProteins 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 MetabolismIn 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

COOHCitric acid

H2C COOH

COOHHOC

H2C COOH

+ H+Pyruvic

acidAcetyl

coenzyme A

C

CH3

O

CH3

C

COOH

O

To electrontransport chain

H2O

CO2

NAD+

KREBSCYCLE

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

acidAcetyl

coenzyme A

C

CH3

O

CH3

C

COOH

O


H2O

CO2

NAD+

KREBSCYCLE

NADH

CoA

CoA

2

1


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

acidAcetyl

coenzyme A

C

CH3

O

CH3

C

COOH

O


H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

CoA

CoA

2

3

O

1


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

acidAcetyl

coenzyme A

C

CH3

O

CH3

C

COOH

O


H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

O

CoA

O

CoA

2

3

4

1


CO2

+ H+NADH

CO2

+ H+

C

CH2

COOH

O

Oxaloacetic acid

COOH

H2C COOH

H2C COOHSuccinic 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

acidAcetyl

coenzyme A

C

CH3

O

CH3

C

COOH

O


ADP

H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

ATP

GTP

O

CoA

CoA

O

CoA

2

3

4

5

1


CO2

+ H+NADH

CO2

+ H+

To electrontransportchain

C

CH2

COOH

O

Oxaloacetic acid

COOH

H2C COOH


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

acidAcetyl

coenzyme A

C

CH3

O

CH3

C

COOH

O


ADP

FADH2

COOH

COOH

H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

ATP

GTP

CoA

CoA

O

CoA

2

3

4

5

6

O

1


CO2

+ H+NADH

CO2

+ H+


C

CH2

COOH

O

Oxaloacetic acid

COOH

HCOH

CH2

COOH

COOH

H2C COOH


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

acidAcetyl

coenzyme A

C

CH3

O

CH3

C

COOH

O


ADP

FADH2

COOH

COOH

H2O

H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

ATP

GTP

CoA

CoA

O

CoA

2

3

4

5

6

7

O

1


CO2

+ H+NADH

CO2

+ H+


C

CH2

COOH

O

Oxaloacetic acid

COOH

+ H+NADH

HCOH

CH2

COOH

COOH

H2C COOH


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

acidAcetyl

coenzyme A

C

CH3

O

CH3

C

COOH

O


ADP

FADH2

COOH

COOH

H2O

H2O

CO2

NAD+

KREBSCYCLE

NADH

NADH

ATP

GTP

CoA

CoA

O

CoA

2

3

4

5

6

7

8

O

Krebs Cycle Reactions


Metabolic AdaptationsDuring 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 StateSoon 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 StateDuring the absorptive state, most body cells

are concerned with

producing ATP

by oxidizing

glucose


AMINO ACIDS GLUCOSE TRIGLYCERIDES(in chylomicrons)

Blood

GLUCOSE

GASTROINTESTINALTRACT

+ H2O +CO2

MOST TISSUES

Oxidation

ATP

1


Blood

GLUCOSE


HEPATOCYTES IN LIVER

+ H2O +CO2

MOST TISSUES

Oxidation

ATP

Fatty acids

Triglycerides

Glyceraldehyde3-phosphate Glycogen

Glucose

+ H2O +CO2 ATP

1

2


Blood

GLUCOSE



+ H2O +CO2

MOST TISSUES

Oxidation

ATP

Triglycerides

ADIPOSE TISSUE

VLDLs

Triglycerides

Fatty acids

Triglycerides


Glucose

+ H2O +CO2 ATP

1

2

3


Blood

GLUCOSE


GLUCOSE


SKELETALMUSCLE

Storage

+ H2O +CO2

MOST TISSUES

Oxidation

ATP

Triglycerides

ADIPOSE TISSUE

VLDLs

Fattyacids

Triglycerides

Glyceraldehyde3-phosphate

Glucose

Fatty acids

Triglycerides


Glucose

GlycogenGlycogen

+ H2O +CO2 ATP

1

2

3

4

4


Blood

GLUCOSE


GLUCOSE


SKELETALMUSCLE

Storage

+ H2O +CO2

MOST TISSUES

Oxidation

ATP

Triglycerides

ADIPOSE TISSUE

VLDLs

Triglycerides

Fattyacids

Triglycerides


Glucose

Fatty acids

Triglycerides


Glucose

GlycogenGlycogen

+ H2O +CO2 ATP

1

2

3

4 5

4


Blood

GLUCOSE


GLUCOSE


SKELETALMUSCLE

Storage

+ H2O +CO2

MOST TISSUES

Oxidation

ATP

Triglycerides

ADIPOSE TISSUE

VLDLs

Triglycerides

Fattyacids

Triglycerides


Glucose

Keto acids

Fatty acids

Triglycerides


Glucose

GlycogenGlycogen

+ H2O +CO2 ATP

1

2

3

4 5

6

4


Blood

GLUCOSE


GLUCOSE


SKELETALMUSCLE

Storage

+ H2O +CO2

MOST TISSUES

Oxidation

ATP

Triglycerides

ADIPOSE TISSUE

VLDLs

Triglycerides

Fattyacids

Triglycerides


Glucose

Keto acids

Fatty acidsProteins

Triglycerides


Glucose

GlycogenGlycogen

+ H2O +CO2 ATP

1

2

3

4 5

67

4


Blood

GLUCOSE


GLUCOSE


SKELETALMUSCLE

Storage

+ H2O +CO2

MOST TISSUES

Oxidation

ATP

Triglycerides

ADIPOSE TISSUE

VLDLs

Triglycerides

Fattyacids

Triglycerides


Glucose

Keto acids

Fatty acidsProteins

Triglycerides


Glucose

GlycogenGlycogen

ProteinsProteins

+ H2O +CO2 ATP

1

2

3

4 5

67

8

4


The Postabsorptive StateAbout 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 StateThe 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 TISSUESKELETAL MUSCLE TISSUE

OTHER TISSUES

1

Liver glycogen

Glucose

LIVER

Glycerol

Blood

HEART

Fatty acidsGlycerol

TriglyceridesADIPOSE TISSUE

SKELETAL MUSCLE TISSUE

OTHER TISSUES

2

Fatty acids

1

Liver glycogen

Glucose

LIVER

Lactic acid

Glycerol

Blood

HEART

Fatty acidsGlycerol



OTHER TISSUES

3

2

Fatty acids

1

Liver glycogen

Keto acids

Glucose

Amino acids

LIVER

Lactic acid

Glycerol

Blood

HEART

Muscle proteins

Fatty acidsGlycerol


Fasting orstarvation


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




OTHER TISSUES

Fatty acids

ProteinsAmino acids

Amino acidsFatty 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




OTHER TISSUES

Fatty acids

ProteinsAmino 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




OTHER TISSUES

Fatty acids

ProteinsAmino acids


Lactic acid

ATP

ATPATP

ATP

ATP

4

5

5

67

4

3

5

4

2

Fatty acids

1

Liver glycogen

Keto acids

Glucose

Amino acids

LIVER

Fatty acids

Lactic acid

Ketone bodies

Glycerol

Blood

NERVOUSTISSUE Ketone

bodiesGlucose

Starvation

HEART

Fatty acids

Muscle proteins

Fatty acidsGlycerol




Ketone bodies

OTHER TISSUES

Fatty acids

ProteinsAmino acids


Ketone bodies

Lactic acid

ATP

ATP

ATP

ATP

ATP

ATP

ATP

ATP

ATP ATP

4

5

8

5

6

88

7

4

3

5

4

2

8

1

Liver glycogen

Keto acids

Glucose

Amino acids

LIVER

Fatty acids

Lactic acid

Ketone bodies

Glycerol

Blood

NERVOUSTISSUE Ketone

bodiesGlucose

Starvation

HEART

Fatty acids

Muscle proteins

Fatty acidsGlycerol



Ketone bodies

OTHER TISSUES

Fatty acids

ProteinsAmino acids

Glucose6-phosphate

Pyruvic acid

Lacticacid

Muscle glycogen

(aerobic) (anaerobic)


Ketone bodies

Lactic acid

ATP

O2

ATP

ATP

ATP

ATP

ATP

ATP

ATP

ATP

ATP

ATP ATP

+ O2–

4

5

8

5

6

88

7

4

3

9

5

4

2

8


Basal Metabolic RateThe 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 TemperatureDespite 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 BalanceHeat 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 ThermostatThe 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


ThermoregulationIf 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


NutritionNutrients 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


NutritionGuidelines 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


NutritionIn this nutrition pyramid the six color bands

represent the five basic food groups plus oils.

Foods from all bands are needed each day


NutritionEssential 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


NutritionVitamins 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 DeficienciesVitamin 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 DeficienciesVitamin 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


Vitamin DeficienciesNiacin (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


Vitamin DeficienciesFolic 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


ObesityObesity 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


ObesityFactors 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

Science

Chapter 25