Download Food Processing and Utilization

Food Processing
Module 22.2: Nutrient pool substrates

Nutrient pool supplies molecules for
catabolism, anabolism, and to fuel ATP
production
◦
◦
ATP used for metabolic makeover inside cell
Organic compounds used for 2-carbon
substrate molecules for mitochondrial activities
The centrality of the nutrient
pool to both anabolism and
catabolism
Structural, functional, and storage components
Triglycerides
Organic compounds
that can be
absorbed by cells
are distributed to
cells throughout
the body by the
bloodstream.
Nutrient Fatty acids
pool
Glycogen
Proteins
Glucose
Amino acids
Three-carbon chains
Two-carbon chains
MITOCHONDRIA
KEY
Citric
acid
cycle
ATP
Coenzymes Electron
transport
system
O2
= Catabolic pathway
H2 O
= Anabolic pathway
CO2
Figure 22.2
1
Module 22.2: Nutrient pool substrates

When nutrients absorbed from digestive tract
are insufficient for cellular metabolism, energy
reserves come from various cells
◦
Liver cells store triglycerides and glycogen

◦
Fatty acids and glucose can be released
Adipocytes store triglycerides

◦
Fatty acids can be released
Skeletal muscle cells store glycogen

Amino acids can be released
The use of the body’s metabolic
reserves to maintain normal
nutrient levels in the blood
Nutrients obtained through
digestion and absorption
Neural tissue requires a
continuous supply of
glucose. During starvation,
other tissues shift to fatty
acid or amino acid
catabolism, conserving
glucose for neural tissue.
Liver cells store triglycerides and
glycogen reserves. If absorption by the
digestive tract fails to maintain normal
nutrient levels, the triglycerides and
glycogen are broken down and the
fatty acids and glucose are released.
Nutrients distributed
in the blood
Adipocytes convert excess fatty acids to
triglycerides for storage. If absorption by
the digestive tract and reserves in the
liver fail to maintain normal nurtient
levels, the triglycerides are broken down
and the fatty acids released.
Skeletal muscles at rest metabolize fatty
acids and use glucose to build glycogen
reserves. Amino acids are used to
increase the number of myofibrils. If the
digestive tract, adipocytes, and liver are
unable to maintain normal nutrient levels,
the contractile proteins can be broken
down and amino acids released into the
circulation for use by other tissues.
Cells in most tissues
continuously
absorb and
catabolize glucose.
Figure 22.2
2
Module 22.2: Nutrient pool
substrates

Cellular catabolic and anabolic pathways
◦
Cells must synthesize some organic molecules


◦
◦
Insufficient nutrients from nutrient pool and diet
Nutrients are often used to create 2-carbon chains for
mitochondrial ATP production
Oxygen required must be continuously provided by
diffusion from ECF
CO2 produced must diffuse out of cell to ECF
Module 22.2: Nutrient pool substrates

Cellular nutrient dynamics
◦
Fatty acids


◦
Can be stored as triglycerides
Can be created from acetyl-CoA and triglycerides
Glucose


Can be stored as glycogen (glycogenesis)
Can be created from:



Glycogen catabolism (glycogenolysis)
Smaller carbon chain anabolism (gluconeogenesis)
Can be used to make two 3-carbon chains for ATP
production (glycolysis)
Module 22.2: Nutrient pool substrates

Cellular nutrient dynamics (continued)
◦
Amino acids


Can be stored as proteins
Can be created from:


3-carbon chains
Protein catabolism (only during starvation)
KEY
= Catabolic pathway
A general overview of the catabolic and anabolic pathways of cells
= Anabolic pathway
Fatty acids
can be
stored as
triglycerides.
Nutrient
pool
Proteins
Glycogen
Triglycerides
Stored
triglycerides
can be broken
down into
fatty acids.
In glycogenesis,
glycogen is
synthesized from
glucose.
Fatty acids
The release of
glucose from
glycogen is called
glycogenolysis.
Amino acids
Glucose
The breakdown
of a fatty acid
releases glycerol
and acetyl-CoA
suitable for use
by mitochondria.
Gluconeogenesis: glucose
synthesis from
smaller carbon
chains.
Glycolysis:
glucose breakdown into two
three-carbon
molecules/chains
The primary use of amino
acids is the synthesis of
proteins. Amino acids are
seldom broken down if other
energy sources are available.
However, in starvation the
proteins of muscle tissues
are mobilized, releasing
amino acids that can be
catabolized by other tissues.
Three-carbon chains
Two-carbon chains
Fatty acid synthesis
begins with acetyl-CoA.
Because this is the
common intermediary
for all aerobic catabolic
pathways, fatty acids
can be synthesized from
excess carbohydrates or
amino acids.
MITOCHONDRIA
Citric
acid
cycle
Coenzymes
ATP
Electron
transport
system
O2
H2O
CO2
CO2 must leave the cytosol by
diffusion into the ECF, and the
bloodstream must continuously
absorb CO2 in peripheral tissues
and eliminate it at the lungs to
prevent potentially dangerous
changes in body fluid pH.
O2 must be
continuously
provided by
diffusion from the
ECF. This requires
normal respiratory
function and
adequate tissue
perfusion.
Figure 22.2
3
Module 22.2 Review
a. Define nutrient pool.
b. Why do cells engage
in catabolism?
c. Why do cells make
new compounds?
Section 2: Digestion and Metabolism of
Organic Nutrients

Overview of digestive process
◦ Oral cavity (mechanical processing and chemical digestion of
carbohydrates and lipids)
◦ Stomach (acidic chemical digestion)
◦ Duodenum (various enzymes catalyze catabolism of all organic
molecules needed by cells)
◦ Jejunum and Ileum (nutrient absorption)
 Nutrients stored and processed by liver
◦ Large intestine (water reabsorbed, nutrients and vitamins
produced by bacteria, feces eliminated)
Steps in the Process of Digestion
In the oral cavity, saliva dissolves some organic
nutrients, and mechanical processing with
the teeth and tongue disrupts the physical
structure of the material and provides access
for digestive enzymes. Those enzymes begin
the digestion of complex carbohydrates
(polysaccharides) and lipids.
In the stomach, the material is further broken
down physically and chemically by stomach
acid and by enzymes that can operate at an
extremely low pH.
In the duodenum, buffers from the pancreas and
liver moderate the pH of the arriving chyme, and
various digestive enzymes are secreted by the
pancreas that catalyze the catabolism of
carbohydrates, lipids, proteins, and nucleic acids.
Nutrient absorption then occurs in the small
intestine, primarily in the jejunum, and the
nutrients enter the bloodstream.
Indigestible materials and wastes enter the large
intestine, where water is reabsorbed and bacterial
action generates both organic nutrients and
vitamins. These organic products are absorbed
before the residue is ejected at the anus.
Most of the nutrients absorbed by the digestive
tract end up in a tributary of the hepatic portal
vein that ends at the liver. The liver absorbs
nutrients as needed to maintain normal levels
in the systemic circuit.
Within peripheral tissues, cells absorb the
nutrients needed to maintain their nutrient pool
and ongoing operations.
Figure 22 Section 2
Module 22.3: Carbohydrates


Carbohydrates are usually preferred substrates
for catabolism and ATP production when
resting
Steps of carbohydrate digestion
◦
In mouth, salivary amylase digests complex
carbohydrates into disaccharides and trisaccharides

◦
Enzyme active only down to pH 4.5 and denatured in
stomach
At duodenum, pancreatic alpha-amylase
continues carbohydrate digestion
Module 22.3: Carbohydrates

Steps of carbohydrate digestion (continued)
◦
In jejunum, brush border enzymes finish
carbohydrate digestion down to simple sugars
(monosaccharides)



◦
Maltase (digests maltose: glucose + glucose)
Sucrase (digests sucrose: glucose + fructose)
Lactase (digests lactose: glucose + galactose)
In large intestine, remaining indigestible
carbohydrates (such as cellulose) are food source
for colonic bacteria

Produce intestinal gas (flatus) during metabolic activities
Module 22.3: Carbohydrates

Carbohydrate absorption and transport
◦
Transported into small intestine epithelial cells

◦
Leave cells by facilitated diffusion through basolateral
surface
Enter cardiovascular capillaries to transport to liver
in hepatic portal vein

Processed by liver to maintain glucose levels (~90 mg/dL)


Released as glucose or
Stored as glycogen
Module 22.3: Carbohydrates

Cellular use of digested carbohydrates
◦
Generally preferred for catabolism

◦
◦
Proteins and lipids more important for structural
components of cells and tissues
In skeletal muscle, stored as glycogen
In most tissues, transported into cell by carrier
molecule (regulated by insulin)


May be converted to ribose
May be converted to 2 pyruvate molecules in glycolysis


Produces 2 ATP
Pyruvates used by mitochondria

Uses 3 O2, generates 3 CO2, 6 H2O, 34 ATP
The events in carbohydrate catabolism and ATP production from glucose
GLUCOSE
(6-carbon)
ATP
Carbohydrates (such as glucose) are generally
preferred for catabolism because proteins and
lipids are more important as structural
components of cells and tissues.
In most tissues, the
transport of glucose into the
cell is dependent on the
presence of a carrier protein
stimulated by insulin.
Inside the cell, the glucose may be converted to
another simple sugar, such as ribose, used to
Insulin
build glycoproteins, other structural materials,
or nucleic acids. They may also be converted to
glycerol for the synthesis of glycerides.
Other simple sugars
If needed to provide energy, the 6-carbon glucose
molecule is broken down into two 3-carbon
molecules of pyruvate. This anaerobic process,
called glycolysis, yields a net gain of 2 ATP for
every glucose molecule broken down.
Pyruvate
(3-carbon)
Pyruvate
(3-carbon)
CO2
Coenzyme A
Each pyruvate molecule can then be used by
mitochondria, after conversion to acetyl-CoA.
Acetyl-CoA
(2-carbon)
Citric
acid
cycle
ATP
Coenzymes
Electron
transport
system
O2
For each molecule of pyruvate processed by
mitochondria, the cell gains 17 ATP, consumes
3 molecules of O2, and generates 3 molecules of
CO2 and 6 molecules of water. Thus for each pair
of pyruvate molecules catabolized, the cell gains
34 ATP.
H2O
CO2
Figure 22.3
Module 22.3 Review
a. Describe the source of
intestinal gas.
b. Explain the role of
glycogen in cellular
metabolism.
c. Explain why
carbohydrates are
preferred over
proteins and fats as an
energy source.
Module 22.4: Catabolism of glucose

Glycolysis
◦
Anaerobic process making two 3-carbon
pyruvate from one 6-carbon glucose
Occurs in cytosol
Produces a net gain of 2 ATP
◦
◦

Also produces hydrogen atoms that are transferred
by NAD to mitochondria for ETS
Module 22.4: Catabolism of glucose

Steps of glycolysis
◦
◦
◦
Phosphate group attached to glucose in cytosol
2nd phosphate attached (cost of 2 ATP)
6-carbon molecule split into two 3-carbon
molecules
Another phosphate attached to each molecule and
processed further
◦



◦
2 NADH generated
2 ATP generated
2 H2O released
Further processing creates an additional 2 ATP
The steps in glycolysis, the breakdown of a six-carbon
glucose molecule into two three-carbon pyruvate molecules
INTERSTITIAL
FLUID
Glucose
ATP
CYTOSOL
ADP
Steps in Glycolysis
Glucose-6-phosphate
ATP
As soon as a glucose molecule
enters the cytosol, a phosphate
group is attached to the molecule.
ADP
Fructose-1,6-biphosphate
A second phosphate group is
attached. Together, steps 1 and 2
cost the cell 2 ATP.
The six-carbon chain is split
into two three-carbon molecules,
each of which then follows the
rest of this pathway.
Another phosphate group is
attached to each molecule, and
NAD•H is generated from NAD.
Dihydroxyacetone
phosphate
Glyceraldehyde
3-phosphate
2
2 NAD
2 NAD•H
From mitochondria
To mitochondria
1,3-Bisphosphoglycerate
2 ADP
One ATP molecule is formed for
each molecule processed.
The atoms in each molecule are
rearranged, releasing a
molecule of water.
2 ATP
3-Phosphoglycerate
2 H2O
Energy Summary
Steps 1 & 2:
–2
ATP
Step 5: +2 ATP
Step 7: +2 ATP
NET GAIN:+2 ATP
Phosphoenolpyruvate
A second ATP molecule is formed
for each molecule processed.
Step 7 produces 2 ATP molecules.
2 ADP
2 ATP
Pyruvate
To mitochondria
Figure 22.4
1
Module 22.4: Catabolism of glucose

Summary of aerobic ATP production
◦
◦
◦
◦
◦
4 ATP from NADH produced in glycolysis
24 ATP from NADH generated in citric acid
cycle
4 ATP from FADH2 generated in citric acid
cycle
2 ATP via GTP produced during enzymatic
reactions
34 ATP total
Figure 22.4
2
Module 22.4 Review
a. List the molecular
products from a glucose
molecule after glycolysis.
b. Identify when most of the
CO2 is released during
the complete catabolism
of glucose.
c. Explain when glycolysis
may be important in
cellular metabolism.
Module 22.5: Lipids

Steps of lipid digestion
◦
In mouth, mechanical processing and chemical
digestion by lingual lipase
In stomach, lingual lipase continues to function but
can only access surface of lipid drops that have
formed
In duodenum
◦
◦


Bile salts break up lipid drops into smaller droplets (=
emulsification)
Pancreatic lipase digests triglycerides into fatty acids,
monoglycerides, and glycerol

Forms micelles (lipid–bile salt complexes)
Module 22.5: Lipids
Absorption and transport of digested lipids

◦
◦
Lipids diffuse from micelle into intestinal epithelial cell
Intracellular anabolic reactions synthesize new triglycerides from
digested lipids
New triglycerides packaged in chylomicrons (chylos, milky lymph,
mikros, small) and released via exocytosis
Chylomicrons diffuse into intestinal lacteals due to their size
◦
◦

◦
Transported through lymphatic vessels (including thoracic duct) to
bloodstream
Enzyme in capillaries (lipoprotein lipase) breaks down
chylomicron and releases digested lipids to tissues
Module 22.5: Lipids

Digested lipid distribution and processing
◦
Tissues that use or process digested lipids

Skeletal muscles


Adipose tissue


Use fatty acids to generate ATP for contraction and to convert
glucose to glycogen
Uses fatty acids and monoglycerides to synthesize triglycerides
for storage
Liver

Absorbs intact chylomicrons and extracts triglycerides and
cholesterol from chylomicron
Module 22.5: Lipids
Cholesterol distribution

◦
Released from liver attached to low-density lipoproteins (LDL)
for distribution to peripheral tissues
LDLs absorbed and broken down by lysosomes in cells
◦


◦
High-density lipoproteins (HDL) (plasma proteins from liver)
absorb peripheral cholesterol and return to liver


Cholesterol extracted and used
Unused cholesterol released into bloodstream
Cholesterol released again with LDLs or excreted in bile
Ratio of LDL/HDL and total cholesterol used diagnostically for
cardiovascular problems
Thoracic
duct
The chylomicrons
enter the bloodstream
at the left subclavian
vein, then pass
through the
pulmonary circuit
before entering the
systemic circuit.
Resting skeletal muscles absorb fatty
acids and break them down, using the
ATP provided both to power the
contractions that maintain muscle
tone and to convert
glucose to glycogen.
Capillary walls contain the
enzyme lipoprotein lipase,
which breaks down the
chylomicrons and releases
fatty acids and monoglycerides that can diffuse into the
interstitial fluid.
Adipocytes absorb
the monoglycerides
and fatty acids,
and use them to
synthesize triglycerides for storage.
Lipoproteins and Lipid Transport and Distribution
The liver absorbs chylomicrons, removes the
triglycerides, combines the cholesterol from the
chylomicron with synthesized or recycled
cholesterol, and alters the surface proteins. It then
releases low-density lipoproteins (LDLs) into
the circulation, which deliver cholesterol to
peripheral tissues. Some of the cholesterol is used
by the liver to synthesize bile salts; excess
cholesterol is excreted in the bile.
The HDLs return
the cholesterol to
the liver, where it
is extracted and
packaged in new
LDLs or excreted
with bile salts in
bile.
From the lacteals,
the chylomicrons
proceed along the
lymphatic vessels
and into the
thoracic duct.
Chylomicrons Triglycerides
removed
The LDLs released by the
liver leave the bloodstream
through capillary pores or
cross the endothelium by
vesicular transport.
LDL
Cholesterol
extracted
Excess
cholesterol is
excreted with
the bile salts
HDL
HDL
High
cholesterol
Low
cholesterol
Once in peripheral tissues,
the LDLs are absorbed.
LDL
Lysosomal
breakdown
HDL
Cholesterol
release
Used in synthesis
of membranes,
hormones,
other material
Figure 22.5
Module 22.5 Review
a. What is the difference
between a micelle and
a chylomicron?
b. What does the liver do
with the chylomicrons
it receives?
c. Describe the roles of
LDL and HDL.
Module 22.6: Lipid catabolism and synthesis

Lipolysis (lipid catabolism)
◦
Triglycerides absorbed into cells through
endocytosis

Lysosomal enzymes break down to glycerol and fatty acids


Glycerol

Converted to pyruvate in glycolysis (+ 2 ATP)
Fatty acids

Enzymes convert two carbons to acetyl-CoA directly
(= beta-oxidation) used in mitochondria

More efficient than glucose catabolism (6-carbon glucose =
36 ATP; 6 carbons from FAs = 51 ATP)
Module 22.6: Lipid catabolism and synthesis
Lipid synthesis (lipogenesis)

◦
Begins with acetyl-CoA

◦
Almost any organic substrate (lipids, amino acids, carbohydrates) can
be converted to acetyl-CoA
Fatty acids synthesized from acetyl-CoA


Series of enzymatic steps (different from beta-oxidation)
Essential fatty acids


◦
Cannot be synthesized and must be obtained from diet
Examples: linolenic acid (omega-3 fatty acid) and linoleic acid
(omega-6 fatty acid)
Structural and functional lipids created from fatty acids

Fatty acids + glycerol (from glycolysis) = triglycerides
CYTOSOL
The glycerol required for triglyceride
production is synthesized from one of the
intermediate products of glycolysis.
Steroids
Triglycerides
Glucose
All of the other structural and functional
lipids can be synthesized from fatty acids.
Glycerol
Cholesterol
Fatty acid synthesis involves a reaction sequence
quite distinct from that of beta-oxidation. As a
result, body cells cannot build every fatty acid
they can break down. For example, our cells lack
the enzymes to insert double bonds in the proper
locations to synthesize two 18-carbon fatty acids
synthesized by plants: linolenic acid (an
omega-3 fatty acid) or linoleic acid (an
omega-6 fatty acid). However, these fatty acids
are needed to synthesize prostaglandins and
some of the phospholipids found in plasma
membranes throughout the body. They are
therefore called essential fatty acids, because
they must be included in your diet.
Prostaglandins
Fatty acids
Pyruvate
Phospholipids
Glycolipids
Start
The synthesis of most types of lipids, including
nonessential fatty acids and steroids, begins
with acetyl-CoA. Lipogenesis can use almost
any organic substrate, because lipids, amino
acids, and carbohydrates can be converted to
acetyl-CoA.
CO2
Coenzyme A
ADP
ATP
Acetyl-CoA
Citric
acid
cycle
MITOCHONDRIA
The major pathways for lipogenesis, the synthesis of lipids
Figure 22.6
2

Module 22.6: Lipid catabolism and synthesis
Lipids as energy reserves
◦
◦
Beta-oxidation is very efficient
Can be easily stored as triglycerides

Although water-soluble enzymes cannot access, so
not used for quick energy but for long-term storage
Module 22.6 Review
a. Define beta-oxidation.
b. What molecule plays a
key reactant role in
both ATP production
from fatty acids and
lipogenesis?
c. Identify the fates of
fatty acids.
Module 22.7: Protein digestion and amino
acid metabolism

Steps of protein digestion
◦
◦
In mouth, mechanical processing occurs
In stomach:



Mechanical processing due to churning
Stomach acid denatures protein secondary and tertiary
structures
Pepsin (from parietal cells) attacks certain peptide
bonds

Digests proteins to polypeptide and peptide chains

Module 22.7: Protein digestion and amino
acid metabolism
Steps of protein digestion (continued)
◦
In duodenum:


Enteropeptidase (from duodenal epithelium) converts
trypsinogen (pancreatic proenzyme) to trypsin
Trypsin activates other pancreatic proenzymes


Chymotrypsin, carboxypeptidase, and elastase
Activated pancreatic enzymes digest specific peptide
bonds producing short peptides and amino acids

Module 22.7: Protein digestion and amino
acid metabolism
Digested protein absorption and transport
◦
Epithelial brush border enzymes (peptidases)
finish protein digestion
Amino acids absorbed through:
◦


◦
◦
Facilitated diffusion
Cotransport
Released from epithelial cell basal surface through
same cell transport mechanisms
Amino acids transported to liver through intestinal
capillaries to hepatic portal vein

Module 22.7: Protein digestion and amino
acid metabolism
Amino acid processing in liver
◦
Control of plasma amino acid levels is less
precise than glucose


◦
Normal range: 35–65 mg/dL
Can increase after protein-rich meal
Liver amino acid use


Synthesize plasma proteins
Create 3-carbon molecules for gluconeogenesis

Module 22.7: Protein digestion and amino
acid metabolism
Amino acid processing in liver (continued)
◦
Amino acid catabolism

Deamination (removal of amino group)

Ammonium ions released are toxic

Liver enzymes convert to urea excreted into urine

= Urea cycle
The liver does not control circulating levels
of amino acids as precisely as it does
glucose concentrations. Plasma amino acid
levels normally range between 35 and 65
mg/dL, but they may become elevated after
a protein-rich meal. The liver itself uses
many amino acids for synthesizing plasma
proteins, and it has all of the enzymes
needed to synthesize, convert, or catabolize
amino acids. In addition, amino acids that
can be broken down to 3-carbon molecules
can be used for gluconeogenesis when
other sources of glucose are unavailable.
Amino Acid Synthesis
Liver cells and other body cells can readily synthesize the carbon
frameworks of roughly half of the amino acids needed to synthesize proteins.
There are 10 essential amino acids that the body either cannot synthesize
or that cannot be produced in amounts sufficient for growing children.
In an amination
reaction, an ammonium
ion (NH4+) is used to
form an amino group
that is attached to a
molecule, yielding an
amino acid.
NH4+
H2O
H+
α–Ketoglutarate
Glutamic acid
In a transamination, the amino group of one amino acid gets transferred
to another molecule, yielding a different amino acid. The remaining carbon
chain can then be broken down or used in other ways.
Transaminase
Glutamic acid
Organic acid 1
Organic acid 2
Tyrosine
Figure 22.7
Module 22.7 Review
a.
Name the enzyme secreted by
parietal cells that is necessary
for protein digestion.
b. Identify the processes by which
the amino group is removed.
c. What happens to the
ammonium ions that are
removed from amino acids
during deamination?
Module 22.8: Absorptive and
postabsorptive states

Absorptive state
◦
◦
◦
Period following a meal, when nutrient absorption is
occurring
Commonly continues for ~4 hours
Insulin is primary regulating hormone by stimulating:
1. Glucose uptake and glycogenesis
2. Amino acid uptake and protein synthesis

Others can be involved (GH, androgens, estrogens)
3. Triglyceride synthesis
◦
ATP can be produced from nutrient pool
The activities during the absorptive state following a meal
KEY
Glucose
levels elevated
= Catabolic pathway
= Anabolic pathway
= Stimulation
Insulin
CARBOHYDRATES
LIPIDS
Triglycerides
PROTEINS
Glycogen
Proteins
Insulin
Glucose
Insulin
Lipid levels
elevated
Fatty acids
Glycerol
G
l
y
c
o
l
y
s
I
s
Insulin
Androgens
Estrogens
Growth hormone
ATP
Amino acids
elevated
Amino acids
Insulin,
Growth hormone
Pyruvate
In the absorptive state:
• Insulin stimulates
(1) glucose uptake
and glycogenesis,
(2) amino acid uptake
and protein synthesis,
and (3) triglyceride
synthesis.
• Androgens, estrogens,
and growth hormone
also stimulate protein
synthesis.
• Glycolysis and aerobic
metabolism provide the
ATP needed to power
cellular activities as well
as the synthesis of lipids
and proteins.
CO2
Insulin
Acetyl-CoA
Citric
acid
cycle
ATP
Coenzymes
MITOCHONDRIA
Electron
transport
system
O2
O2
H2O
CO2
Figure 22.8
1
Module 22.8: Absorptive and
postabsorptive states
Postabsorptive state

◦
Period when nutrient absorption in not occurring and body relies
on energy reserves (~12 hours/day)
Metabolic activity focused on mobilizing energy reserves and
maintaining blood glucose
◦



◦
Lipid levels decrease = fatty acids released by adipocytes
Amino acid levels decrease = amino acids released by liver
Glucose levels decrease = glucose released by liver
Coordinated by several hormones

Glucagon, epinephrine, glucocorticoids, growth hormone

Module 22.8: Absorptive and
postabsorptive states
Postabsorptive state (continued)
◦
Catabolism of lipids and amino acids in liver
produce acetyl-CoA

Leads to formation of ketone bodies

Diffuse into blood and are used by other cells as energy
source
Module 22.8: Absorptive and
postabsorptive states

Postabsorptive state (continued)
◦
Hormone effects

Glucocorticoids


Glucagon


Stimulate mobilization of lipid and protein reserves

Enhanced by growth hormone
Stimulates glycogenolysis and gluconeogenesis

Mainly in liver
Epinephrine


Glycogenolysis in skeletal and cardiac muscle
Lipolysis in adipocytes
Module 22.8 Review
a.
Define absorptive state and
postabsorptive state.
b. When and how do ketone
bodies form?
c. How do the absorptive and
postabsorptive states maintain
normal blood glucose levels?
Module 22.9:Vitamins
Nutrition

◦
Absorption of nutrients from food
Vitamins

◦
◦
Organic compounds required in very small
quantities for essential metabolic activities
Two classes
1. Fat-soluble vitamins (A, D3, E, and K)
2. Water-soluble vitamins (B vitamins and C)
Module 22.9:Vitamins
Fat-soluble vitamins

◦
◦
Absorbed primarily from digestive tract with micelles
Vegetables are potential sources


◦
Vitamin D3 produced in skin
Vitamin K produced by intestinal bacteria
Stored in lipid deposits

Gives large bodily reserves


Avitaminosis (vitamin deficiency) rarely occurs with fat-soluble
vitamins
Hypervitaminosis can occur as metabolism from lipid reserves
takes time
Figure 22.9
2
Figure 22.9
2
Module 22.9:Vitamins

Water-soluble vitamins
◦
◦
Most are components of coenzymes
Nutritional sources


◦
◦
B vitamins are found in meat, eggs, and dairy products
Vitamin C is found in citrus fruits
Significant stores of only vitamins B12 and C
Intestinal bacteria produce four of nine B vitamins
Module 22.9:Vitamins

Water-soluble vitamins (continued)
◦
◦
Readily exchanged between body fluid compartments
Most easily absorbed across intestinal wall

◦
B12 requires transport with intrinsic factor
Excess amounts excreted in urine

Hypervitaminosis rarely occurs with water-soluble vitamins
Figure 22.9
4
Figure 22.9
4
Figure 22.9
4
Module 22.9 Review
a. Define nutrition.
b. Identify the two
classes of vitamins.
c. If vitamins do not
provide a source of
energy, what is their
role in nutrition?
Stop
Module 22.10: Nutrition and diet

Balanced diet
◦ Contains all ingredients required for homeostasis






Substrates for ATP production
Essential amino acids
Fatty acids
Vitamins
Electrolytes
Water
◦ Malnutrition
 Unhealthy state from inadequate or excessive nutrient
absorption
Module 22.10: Nutrition and diet

MyPyramid.gov Steps to a Healthier You
◦ U.S. Dept. of Agriculture personalized eating plans
based on current Dietary Guidelines for Americans
◦ Color-coded vertical food groups indicate
recommended proportions






Grains (orange)
Vegetables (green)
Fruits (red)
Milk products (blue)
Meat and beans (purple)
Oils (yellow)
The MyPyramid.gov Steps to a Healthier You
Activity
GRAINS
Make half your grains whole
VEGETABLES
Vary your veggies
FRUITS
Focus on fruits
O
MILK
I
L Get your calcium-rich foods
S
MEAT & BEANS
Go lean with proteins
Figure 22.10 1
Figure 22.10 1
Figure 22.10 1
Module 22.10: Nutrition and diet

Food energy content
◦ Common units are calories or joules (0.239 calories)
 1 calorie = energy to raise temperature of 1 g of water by 1°C
◦ Kilocalories (kcal or Calorie) or kilojoule (kJ) are used for
whole-body metabolism
 1 kCal = energy to raise temperature of 1 kg of water by 1°C
◦ Energy yield of different nutrients varies
 Carbohydrates: 4.18 Cal/g
 Proteins: 4.32 Cal/g
 Lipids: 9.46 Cal/g
◦ Average adult needs 2000–3000 Cal daily
Figure 22.10 2
Figure 22.10 3
Module 22.10: Nutrition and diet

Different nutritional proteins
◦ Complete proteins
 Provide all essential amino acids
 From beef, fish, poultry, eggs, and milk
◦ Incomplete proteins
 Deficient in one or more essential amino acids
 Mostly from plant sources
 Vegetarians and vegans must closely monitor sufficient
combination of plant protein sources
Module 22.10 Review
a.
Define balanced diet.
b. Distinguish between a complete
protein and an incomplete
protein.
c. Of these three—carbohydrates,
lipids, or proteins—which one
releases the greatest number
of Calories per gram during
catabolism?

CLINICAL MODULE 22.11: Metabolic
disorders
Disorders related to diet and digestion
◦
Eating disorders (psychological problems resulting
in abnormal eating habits)

Anorexia nervosa




Self-induced starvation or lack/loss of appetite

Weights commonly 30% below normal
Most common in adolescent Caucasian females
Patients convinced they are too fat
Bulimia


Binge eating followed by vomiting, or use of laxatives or
diuretics
More common than anorexia
CLINICAL MODULE 22.11: Metabolic
disorders

Disorders related to diet and digestion
(continued)
◦
Obesity

Condition of being >20% over ideal weight


U.S. Centers for Disease Control (CDC) estimate:


Due to energy input > energy output
32% of men and 35% of women are obese
Two major categories
1.
Regulatory obesity (failure to regulate food input)

Most common form
2. Metabolic obesity (secondary to underlying malfunction in
cell/tissue metabolism)
CLINICAL MODULE 22.11: Metabolic
disorders

Disorders related to diet and digestion
(continued)
◦
Elevated cholesterol levels



May cause development of atherosclerosis and coronary
artery disease
Recommended <300 mg/day
High LDL levels can lead to deposits in peripheral tissues
such as blood vessels
CLINICAL MODULE 22.11: Metabolic
disorders
Nutritional/metabolic disorders

◦
Phenylketonuria (PKU)

Inability to convert phenylalanine to tyrosine

◦
Essential to synthesis of:

Norepinephrine

Epinephrine

Dopamine

Melanin
Protein deficiency disease


Liver unable to produce plasma proteins leading to edema
Example: kwashiorkor
CLINICAL MODULE 22.11: Metabolic
disorders

Nutritional/metabolic disorders (continued)
◦
Ketoacidosis

Acidification of blood due to ketone body production


Occurs when glucose supplies are limited


◦
Leads to ketosis
Fatty acid and amino acid catabolism in liver leads to acetyl-CoA
production and generation of ketones
In extreme cases, may cause coma, cardiac arrhythmias,
and death
Gout (insoluble urea crystal formation)

Commonly in joints (gouty arthritis)
CLINICAL MODULE 22.11 Review
a. Identify and briefly define
two eating disorders.
b. Define protein deficiency
disease and cite an
example.
c. Briefly describe
phenylketonuria (PKU).
Section 3: Energetics and Thermoregulation

Energetics
◦ Study of energy flow and energy conversion
◦ Basal metabolic rate (BMR)
 Minimum resting energy expenditure of awake, alert person
 Various factors can affect BMR
 Person’s size or weight
 Level of physical activity
 Common benchmark for energetics studies
 Direct measurement method
 Measuring respiratory activity and assuming 4.825 Cal/L oxygen consumed
 Average is 70 Cal/hr
1000
800
Calories per hour
The approximate number of
Calories expended per hour
at various levels of physical
exertion
Estimated Calories expended
by a 70-kg individual
600
400
200
0
Resting
Slow
walking
Speed
walking
Climbing
stairs
Jogging
Competitive
swimming
Figure 22 Section 3
2
Section 3: Energetics and Thermoregulation

Thermoregulation
◦ Homeostatic control of body temperature
 Maintaining food intake adequate to support body activities
◦ Catabolic reactions generating ATP
 40% of energy used to form ATP
 60% released as heat
◦ Many enzymes and metabolic activities require a
specific temperature range
Module 22.12: Appetite regulation


Appetite is controlled by two areas of
hypothalamus
1. Feeding center
2. Satiety center

Causes inhibition of feeding center
Regulation of appetite can occur on two levels
1. Short-term regulation
2. Long-term regulation
Module 22.12: Appetite regulation

Short-term regulation of appetite
◦ Stimulation of satiety center
 Elevation of blood glucose levels
 Hormones of digestive tract (like CCK)
 Digestive tract wall stretching
◦ Stimulation of feeding center
 Neurotransmitters
 Example: neuropeptide Y or NPY from hypothalamus
 Ghrelin
 Hormone secreted by gastric mucosa when stomach is empty
Module 22.12: Appetite regulation

Long-term regulation of appetite
 Leptin
 Peptide hormone secreted by adipocytes
 Stimulates satiety center and suppresses appetite
 Effects are gradual
Short-Term Regulation of Appetite
Stimulation of Satiety Center
Hypothalamus
Satiety center
Elevated bood glucose levels depress
appetite, and low blood glucose
stimulates appetite. The likely
mechanism is glucose entry stimulating
the neurons of the satiety center.
Several hormones of the digestive tract,
including CCK, suppress appetite
during the absorptive state.
Feeding center
Stimulation of stretch receptors along
the digestive tract, especially in the
stomach, causes a sense of satiation
and suppresses appetite.
Long-Term Regulation of Appetite
Stimulation of Feeding Center
Several neurotransmitters have
been linked to appetite regulation.
Neuropeptide Y (NPY), for example,
is a hypothalamic neurotransmitter that
(among other effects) stimulates the
feeding center and increases appetite.
The hormone ghrelin (GREL-in),
secreted by the gastric mucosa,
stimulates appetite. Ghrelin levels are
high when the stomach is empty, and
decline as the stomach fills.
When appetite outpaces energy usage,
excess calories are stored as fat in
adipose tissue. Leptin is a peptide
hormone released by adipose tissues
as they synthesize triglycerides. In the
CNS it stimulates the satiety center
and suppresses appetite. The effects
are gradual, and it is probably involved
in long-term regulation of food intake.
Mechanisms in the control
of appetite
Figure 22.12
Module 22.12 Review
a.
What hormone inhibits the
satiety center and stimulates
appetite in the short-term?
b. Describe leptin and its effect on
appetite.
c. How might a lack of
Neuropeptide Y in the
hypothalamus affect the
control of appetite?
Module 22.13: Thermodynamics

Thermodynamics
◦ About 40% of energy from catabolism is
captured as ATP
 Rest is heat that warms surrounding tissues
◦ To maintain body temperature, heat loss and heat
production must be in balance
 Varying activities and environmental conditions affect
heat balance
Module 22.13: Thermodynamics

Primary heat transfer mechanisms
1. Radiation (infrared radiation from warm objects)
 ~50% of body heat lost by radiation
2. Convection (conductive heat loss due to air
movement)
3. Evaporation (water loss from moist areas)
 Insensible perspiration (from alveoli and skin)
 Sensible perspiration (from sweat glands)
4. Conduction (direct transfer through physical
contact)
Primary Mechanisms of Heat Transfer
Radiation: Warm objects lose heat energy as infrared
radiation. More than 50 percent of the heat you lose
indoors is attributable to radiation.
The primary
mechanisms of
heat transfer
between the body
and the surrounding
environment
Convection: This process results from conductive heat
loss to the air that overlies the surface of the body.
Convection accounts for roughly 15 percent of the
body’s heat loss indoors
Evaporation: When water changes from a liquid to a
vapor, evaporation absorbs energy and cools the
surface where it occurs. Insensible perspiration—the
evaporation of water across epithelia, from alveolar
surfaces, and from the skin—accounts for roughly 20
percent of heat loss indoors. The water in sweat is
termed sensible perspiration.
Conduction: This process, which is the direct transfer
of energy through physical contact, is generally not an
effective mechanism for gaining or losing heat. When
you are standing, conductive losses are negligible.
Figure 22.13 1
The effects of a
failure to control
body temperature
Underlying physical or °F
environmental condition
114
CNS damage
Heat stroke
Disease-related fevers
Severe exercise
Active children
110
106
102
°C
44 Severely impaired
42
38
98
Early mornings in
cold weather
94
36
34
90
32
86
30
82
28
26
Hypothermia
for open heart
surgery
78
74
Impaired
40
Normal range (oral)
Severe exposure
Thermoregulatory
capabilities
24
Major
physiological effects
Death
Proteins denature
Convulsions
Cell damage
Disorientation
Effective
Systems normal
Impaired
Severely impaired
Lost
Disorientation
Loss of
muscle control
Loss of
consciousness
Cardiac arrest
Death
Figure 22.13 2
Module 22.13 Review
a.
Define insensible perspiration.
b. What heat transfer process
accounts for about one-half of
an individual’s heat loss when
indoors?
c. How is heat loss different
between conduction and
convection?
Module 22.14: Thermoregulation

Thermoregulation
◦
◦
Heat loss and heat gain involve many systems
Coordinated by two centers in hypothalamus
preoptic area
1. Heat-loss center
2. Heat-gain center
Module 22.14: Thermoregulation

Responses to high body temperature
◦
◦
Behavioral changes (moving to shade, pool, etc.)
Vasodilation and shunting of blood to skin
surface

◦
Radiational and convective heat loss increases
Sweat production

◦
Increases evaporative heat loss
Respiratory heat loss

Depth of respiration increases to increase evaporative
heat loss from lungs
Preoptic area
Heat-loss center
Heat-gain center
Responses Coordinated by the Heat-Loss
Center When Body Temperature Rises
Behavioral Changes: A sense
of discomfort leads to behavioral
responses—getting into the shade, going
into the water, or taking other steps that
reduce body temperature.
Vasodilation and Shunting of Blood to
Skin Surface: The inhibition of the
vasomotor center causes peripheral
vasodilation, and warm blood flows to the
surface of the body. The skin takes on a
reddish color, skin temperatures rise, and
radiational and convective losses increase.
Radiation
Convection
Sweat Production: As blood flow to the
skin increases, sweat glands are stimulated
to increase their secretory output. The
perspiration flows across the body surface,
and evaporative heat losses accelerate.
Maximal secretion, if completely evaporated,
would remove 2320 Cal per hour.
Respiratory Heat Loss: The respiratory
centers are stimulated, and the depth of
respiration increases. Often, the individual
begins respiring through an open mouth
rather than through the nasal passageways,
increasing evaporative heat losses through
the lungs.
Figure 22.14
Module 22.14: Thermoregulation

Responses to low body temperature
◦
Increased generation of body heat

Nonshivering thermogenesis


Shivering thermogenesis

◦
Release of hormones that increase metabolic rate
Increased muscle tone leading to brief contractions
Conservation of body heat


Vasoconstriction of vessels near body surface
Countercurrent exchange of heat

Transfer of heat from deep arteries to deep veins
Responses Coordinated by the Heat-Gain Center
When Body Temperature Falls
The heat-gain center responds to low body
temperature in two ways:
Increased Generation of Body Heat
Nonshivering thermogenesis (ther-mō-JEN-e-sis)
involves the release of hormones that increase the
metabolic activity of all tissues. Sympathetic stimulation
of the adrenal medullae releases epinephrine, which
quickly increases the rates of glycogenolysis in liver and
skeletal muscle and the metabolic rate of most tissues.
In shivering thermogenesis, a gradual increase in
muscle tone increases the energy consumption of
skeletal muscle tissue throughout your body. Both
agonists and antagonists are involved, and muscle tone
gradually increases to the point at which stretch receptor
stimulation will produce brief, oscillatory contractions
of antagonistic muscles. In other words, you begin to
shiver. Shivering can elevate body temperature quite
effectively, increasing the rate of heat generation by as
much as 400 percent.
Radiation
Convection
Conservation of Body Heat
Warm
Warm blood
blood from
returns
trunk
to trunk
37°C
24°C
Cooled blood
to distal
capillaries
36.5°–
37°C
The vasomotor center decreases blood flow to the dermis,
thereby reducing losses by radiation and convection. The
skin cools, and with blood flow restricted, it may take on a
bluish or pale color. The epithelial cells are not damaged,
because they can tolerate extended periods at temperatures
as low as 25°C (77°F) or as high as 49°C (120°F).
The deep veins lie alongside the deep arteries, and heat
is conducted from the warm blood flowing outward to the
limbs to the cooler blood returning from the periphery.
This arrangement traps the heat close to the body core
and dramatically reduces heat loss. The transfer of heat,
water, or solutes between fluids moving in opposite
directions is called countercurrent exchange.
23°C
Cool blood
returns
to trunk
Figure 22.14
Module 22.14 Review
a. Name the heat conservation mechanism that
results in the conduction of heat from deep
arteries to adjacent deep veins in the limbs.
b. Describe the role of nonshivering thermogenesis
in regulating body temperature.
c. Predict the effect of peripheral vasodilation on an
individual’s body temperature.