Processing Food and
Nutrition
Chapter 46
Learning Objective 1
•
Describe food processing, including
ingestion, digestion, absorption, and
egestion or elimination
•
Compare the digestive system of a
cnidarian (such as Hydra) with that of an
earthworm or vertebrate
Nutrition
•
The process of taking in and using food
Food Processing
•
Feeding
•
•
Digestion
•
•
breaking down food mechanically, chemically
Absorption
•
•
selection, acquisition, and ingestion of food
nutrients pass from digestive tract into blood
Egestion (elimination)
•
undigested, unabsorbed food discharged
Cnidarians and Flatworms
•
Food digested in gastrovascular cavity
•
•
only one opening
serves as both mouth and anus
Gastrovascular
Cavities
Wastes
Food
Tentacle
Mouth
Food
Enzymes
secreted by
inner layer
Gastrovascular
cavity
(b) Exhalation. Food
absorbed
Gastrodermis
(a) Hydra
Fig. 46-2a, p. 992
(b) Flatworm
Gastrovascular
cavity
Epidermis
Food particles
Pharynx
Mouth
Food
absorbed
Enzymes
Wastes
Lining of
the intestine
Food
Fig. 46-2b, p. 992
Complex Invertebrates and
Vertebrates
•
Digestive tract is complete tube
•
•
As food passes through tube
•
•
with opening at each end
digestion takes place
Parts of digestive tract are specialized
•
to perform specific functions
Complete Digestive Tract
Crop
Gizzard
Esophagus
Intestine
Pharynx
Mouth
Anus
Wastes
Food
Fig. 46-3, p. 992
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KEY CONCEPTS
•
Food processing includes ingestion,
digestion, absorption, and elimination
Adaptations for Obtaining Food
KEY CONCEPTS
•
Many animal adaptations are associated
with mode of nutrition
Learning Objective 2
•
Trace the pathway traveled by an ingested
meal in the human digestive system
•
Describe the structure and function of
each organ involved
Human Digestive System 1
•
Mouth
•
•
Mechanical, enzymatic digestion of carbohydrates
Mammalian teeth
•
•
•
incisors for biting
canines for tearing food
premolars, molars for crushing and grinding
Teeth and Diet
Incisors
Canines
Premolars
Molars
(a) Carnivore.
Fig. 46-6a, p. 994
Canine
Incisors
Premolars
Molars
(b) Herbivore.
Fig. 46-6b, p. 994
Canines
Incisors
Premolars
Molars
(c) Omnivore.
Fig. 46-6c, p. 994
Tooth Structure
Crown
Enamel
Gum
Pulp cavity
Neck
Pulp
Dentin
Cementum
Root canal
Root
Spongy bone
Nerve
Vein
(a) Human lower molar. Sagittal section
showing the crown, neck, and root.
Artery
(b) X-ray of a healthy
tooth.
Fig. 46-7, p. 995
Human Digestive System 2
•
Three pairs of salivary glands
•
•
secrete saliva (enzyme salivary amylase
digests starch)
Pharynx and esophagus
•
carry food to stomach
Human Digestive System 3
•
Peristalsis
•
•
•
waves of muscular contraction
pushes bolus of food along digestive tract
Stomach
•
•
mechanical digestion by vigorous churning
enzyme pepsin in gastric juice digests
proteins
Peristalsis
Esophagus
Circular muscles
contract,
constricting
passageway and
pushing bolus
ahead
Food bolus
Relaxed
muscle
layer
Longitudinal
muscles
contract,
shortening
passageway
ahead of the
bolus
Sphincter
closed
A bolus is moved
through the
esophagus by
peristaltic
contractions.
Stomach
Relaxed muscle layer
Sphincter
open
Stomach
When the
sphincter (ring of
muscle) at the
entrance of the
stomach opens,
food enters the
stomach.
Fig. 46-8, p. 995
Human Digestive System 4
•
Rugae
•
•
•
folds in stomach wall
expand as stomach fills with food
Gastric glands secrete
•
•
hydrochloric acid
pepsinogen (precursor of pepsin)
Stomach Structure
Visceral peritoneum
Esophagus
Sphincter
Circular muscle layer
Longitudinal muscle layer
Oblique muscle layer
Pyloric sphincter
Duodenum
Rugae
Fig. 46-9a, p. 996
Openings into
gastric glands
Gastric
glands
Epithelium
Lymph nodule
Gastric mucosa
Fig. 46-9b (1), p. 996
Chief cell
Parietal cell
Nuclei
Surface epithelium
Chief cells
Parietal cells
Gastric glands
Gastric glands
Fig. 46-9b (2), p. 996
Human Digestive System 5
•
Chyme
•
•
•
•
soup of partly digested food
leaves stomach through pylorus
enters small intestine in spurts
Duodenum
•
•
•
location of most enzymatic digestion
produces several digestive enzymes
receives secretions from liver and pancreas
Structure of Digestive Tract
VISCERAL
PERITONEUM
Lymph nodule
Villi
Blood vessels
SUBMUCOSA
Nerve fibers
MUCOSA
MUSCLE LAYER
Inner circular fibers
Outer longitudinal fibers
Fig. 46-5, p. 993
Human Digestive System 6
•
Liver produces bile
•
•
Pancreas releases enzymes
•
•
which emulsifies fats
digest protein, lipid, carbohydrate, RNA, DNA
Trypsin and chymotrypsin
•
digest polypeptides to dipeptides
Human Digestive System 7
•
Pancreatic lipase
•
•
degrades fats
Pancreatic amylase
•
digests complex carbohydrates
Liver and Pancreas
Stomach
Inferior
vena cava
Right lobe
of liver
Right
hepatic
duct
Common
bile duct
Pancreas
Hepatic
portal vein
Pancreatic duct
Gallbladder
Duodenum
Fig. 46-11, p. 998
Human Digestive System 8
•
Large intestine
•
•
•
cecum, colon, rectum, anus
eliminates undigested wastes
incubates bacteria (produce vitamin K, certain
B vitamins)
Human Digestive System
Parotid salivary
gland
Pharynx
Esophagus
Liver
Gallbladder
Ascending colon
lleum
Sublingual salivary
gland
Submandibular
salivary gland
Stomach
Duodenum
Pancreas
Transverse colon
Jejunum
Descending colon
Cecum
Vermiform
appendix
Sigmoid colon
Rectum
Anus
Fig. 46-4, p. 993
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KEY CONCEPTS
•
Various parts of the vertebrate digestive
system are specialized to perform specific
functions; accessory glands (liver,
pancreas, and salivary glands) secrete
fluids and enzymes important in digestion
Learning Objective 3
•
Describe the step-by-step digestion of
carbohydrate, protein, and lipid
Carbohydrate Digestion
•
Polysaccharides
•
•
digested to disaccharide maltose by salivary
and pancreatic amylases
Maltase in small intestine
•
splits maltose into glucose (main product of
carbohydrate digestion)
Protein Digestion
•
Proteins are split
•
•
•
by pepsin in stomach
by proteolytic enzymes in pancreatic juice
Dipeptidases
•
split small peptides into amino acids
Lipid Digestion
•
Lipids are emulsified by bile salts
•
then hydrolyzed by pancreatic lipase
Learning Objective 4
•
What structural adaptations increase the
surface area of the digestive tract?
Surface Area of the Small Intestine
•
Greatly expanded by
•
•
•
folds in wall (rugae)
intestinal villi (projections of mucosa)
microvilli (plasma membrane projections of
epithelial cells of villi)
Villi and Microvilli
Fig. 46-10a, p. 997
Villi
Epithelial cells
lining villus
Capillary network
Nerve fiber
Mucosa
Openings of
intestinal glands
Goblet cells
Intestinal glands
Submucosa
Lacteal
Lymph vessel
Muscle layer
Visceral peritoneum
(b)
Fig. 46-10b, p. 997
Fig. 46-10c, p. 997
Learning Objective 5
•
Compare lipid absorption with absorption
of other nutrients
Nutrient Absorption
•
Nutrients are absorbed through thin walls
of intestinal villi
•
Hepatic portal vein transports amino acids
and glucose to liver
Lipid Absorption 1
•
Fatty acids and monoacylglycerols
•
•
•
enter epithelial cells in intestinal lining
are reassembled into triacylglycerols
then packaged into chylomicron droplets
Lipid Absorption 2
•
Chylomicrons
•
•
•
also contain cholesterol and phospholipids
are covered by a protein coat
Lymphatic system
•
transports chylomicrons to blood circulation
Learning Objective 6
•
Summarize the nutritional requirements for
dietary carbohydrates, lipids, and proteins
•
Trace the fate of glucose, lipids, and
amino acids after their absorption
A Balanced Diet
•
Humans and other animals require
•
•
•
•
•
carbohydrates
lipids
proteins
vitamins
minerals
Carbohydrates 1
•
Most are ingested as polysaccharides
•
starch and cellulose
•
Polysaccharides are complex carbohydrates
•
Fiber
•
mixture of cellulose, other indigestible
carbohydrates
Carbohydrates 2
•
Carbohydrates
•
•
Glucose concentration in blood
•
•
used mainly as energy source
is carefully regulated
Excess glucose
•
•
is stored as glycogen
or converted to fat
Lipids 1
•
Used to
•
•
•
•
provide energy
form components of cell membranes
synthesize steroid hormones, other lipid
substances
Most lipids are ingested as triacylglycerols
Lipids 2
•
Fatty acids are converted to molecules of
acetyl coenzyme A
•
•
which enter citric acid cycle
Excess fatty acids
•
•
are converted to triacylglycerol
stored as fat
Lipids 3
•
Lipids are transported as large molecular
complexes (lipoproteins)
•
Low-density lipoproteins (LDLs)
•
•
deliver cholesterol to cells
High-density lipoproteins (HDLs)
•
•
collect excess cholesterol
transport it to liver
Fat
Metabolism
Fat cell
Fat
Fatty acids
+
Glycerol
Transported in blood
Liver
+ Glycerol
Fatty acid
Used to Acetyl CoA
make
triacylglycerols
Ketone bodies
G3P
Enters
cellular
respiration
Glucose
Converted to
other lipids
Enters
cellular
respiration
Pyruvate or
acetyl CoA
Other
cells
Enters Converted
cellular to other
respiration lipids
Fig. 46-13, p. 1002
Fat cell
Fat
Fatty acids
+
Glycerol
Transported in blood
Liver
+
Fatty acid
Used to
Acetyl CoA
make
triacylglycerols
Ketone bodies
Glycerol
G3P
Enters cellular
respiration
Glucose
Converted to
other lipids
Enters cellular
respiration
Pyruvate or
acetyl CoA
Other
cells
Enters cellular Converted
to other
respiration
lipids
Stepped Art
Fig. 46-13, p. 1002
Proteins 1
•
Proteins serve as enzymes
•
•
Best distribution of essential amino acids
•
•
and essential structural components of cells
in complete proteins of animal foods
Excess amino acids
•
are deaminated by liver cells
Proteins 2
•
Amino groups are converted to urea
•
•
excreted in urine
Remaining keto acids are
•
•
converted to carbohydrate and used as fuel
converted to lipid and stored in fat cells
Protein
Metabolism
AMINO ACIDS
Catabolism Anabolism
Excess amino acids
Deamination
Structural proteins,
hemoglobin, myosin, actin,
enzymes, plasma proteins
NH3 (ammonia) + -keto acids
Liver
Urea
Fat
Pyruvate, ketoglutarate
Acetyl CoA
Enters
cellular
respiration
Ketone bodies
To kidneys Acetyl CoA
Fatty acids + glycerol
Triacylglycerol
Storage in fat cells
Fig. 46-14, p. 1003
Learning Objective 7
•
Describe the nutritional functions of
vitamins, minerals, and phytochemicals
Vitamins
•
Organic compounds required in small
amounts for biochemical processes
•
•
Fat-soluble vitamins
•
•
components of coenzymes
vitamins A, D, E, K
Water-soluble vitamins
•
B and C vitamins
Minerals
•
Inorganic nutrients ingested as salts
•
•
dissolved in food and water
Trace elements
•
•
minerals required in small amounts
(< 100 mg/day)
Phytochemicals
•
Plant compounds that promote health
•
•
many are antioxidants that destroy oxidants
Oxidants
•
•
free radicals, other reactive molecules
damage DNA, proteins, unsaturated fatty
acids by snatching electrons
KEY CONCEPTS
•
Most animals require the same basic
nutrients: carbohydrates, lipids, proteins,
vitamins, and minerals
Learning Objective 8
•
Contrast basal metabolic rate with total
metabolic rate
•
Write the basic energy equation for
maintaining body weight, and describe the
consequences of altering it in either
direction
Measuring Metabolism
•
Basal metabolic rate (BMR)
•
•
body’s cost of metabolic living
Total metabolic rate
•
BMR plus energy used to carry on daily
activities
Energy
•
If energy (kcal) input equals energy output
•
•
If energy output exceeds energy input
•
•
body weight remains constant
body weight decreases
If energy input exceeds energy output
•
body weight increases
Learning Objective 9
•
In general terms, describe the effects of
malnutrition, including both undernutrition
and overnutrition
Undernutrition
•
Form of malnutrition
•
•
•
causes fatigue
depresses immune function
Essential amino acids
•
nutrients most often deficient in diet
Protein Deficiency
Overnutrition
•
Obesity
•
•
•
•
serious form of malnutrition
excess fat accumulates in adipose tissues
factor in heart disease, diabetes mellitus,
other disorders
Person gains weight taking in more energy
(kilocalories) than expended in activity
KEY CONCEPTS
•
•
Basal metabolic rate is the body’s cost of
metabolic living
When energy (kilocalories) input equals
energy output, body weight remains
constant
Learning Objective 10
•
Summarize current hypotheses about the
regulation of food intake and energy
homeostasis, including the roles of leptin
and neuropeptide Y
Leptin
•
Hormone produced by fat cells
•
•
in proportion to body fat
Signals brain about status of energy stores
Effect of Leptin
Neuropeptide Y (NPY)
•
Neurotransmitter produced in hypothalamus
•
•
increases appetite
Slows metabolism when leptin levels and
food intake are low
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