Transcript Chapter 21

Chapter 21
Nutrition and Digestion
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Getting Their Fill of Krill
• The enormous humpback whale eats small
fishes and crustaceans called krill
– Creates "bubble nets" to corral prey
– Strains food from seawater using large
plates of baleen on the upper jaws
• Whales feed in polar regions during the
summer
• In the fall they migrate to warmer oceans,
where they live off body fat and breed
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OBTAINING AND PROCESSING FOOD
21.1 Animals ingest their food in a variety of ways
• All animals eat other organisms
• Animals fall into three dietary categories
– Herbivores: eat plants
– Carnivores: eat other animals
– Omnivores: eat both plants and other
animals
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• Animals obtain and ingest their food in a
variety of ways
– Suspension feeders
• Extract food particles suspended in the
surrounding water
• Examples: whales, clams, tube worms
– Substrate feeders
• Live in or on their food source and eat their
way through it
• Example: caterpillar
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LE 21-1b
Caterpillar
Feces
• Fluid feeders
– Suck nutrient-rich fluids from a living plant
or animal host
– Examples: mosquito, aphid
• Bulk feeders
– Must ingest relatively large pieces of food
– Use diverse structures to kill prey, tear off
pieces, take mouthfuls
– Examples: birds, mammals
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Video: Lobster Mouth Parts
Video: Shark Eating a Seal
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21.2 Overview: Food processing occurs in four
stages
• Ingestion: the act of eating
• Digestion: the breaking down of food into
molecules small enough for the body to absorb
– First mechanically broken into pieces
– Polymers chemically broken down to
monomers by hydrolysis
• All animals need amino acids,
monosaccharides, nucleotides, and fatty
acids
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LE 21-2b
Polymer
Monomers
Proteindigesting
enzymes
Amino acids
Protein
Polysaccharide
Carbohydratedigesting
enzymes
Disaccharide
Monosaccharides
Nucleic aciddigesting
enzymes
Nucleic acid
Nucleotides
Fat-digesting
enzymes
Fat
Glycerol
Fatty acids
• Absorption: molecules taken up by cells lining
the digestive tract
– Transported in blood to body cells
– Formed into body's macromolecules,
broken down for energy, or converted to fat
for storage
• Elimination: passage of undigested material
out of the digestive tract
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LE 21-2a
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
(enzymatic
hydrolysis)
Nutrient
molecules
enter body
cells
Undigested
material
Food
Ingestion
Digestion
Absorption
Elimination
21.3 Digestion occurs in specialized
compartments
• Most animals have an internal compartment in
which digestion occurs outside of cells
– Enables eating of food larger than could be
ingested by phagocytosis
• Cnidarians and flatworms have a
gastrovascular cavity with a single opening
– Digests and absorbs food
– Undigested materials expelled through
mouth
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LE 21-3a
Mouth
Tentacle
Digestive
enzymes
released from
a gland cell
Soft tissues
digested
Food
(Daphnia,
a water
flea)
Food particle
engulfed
Gastrovascular
cavity
Food particle
digested in
food vacuole
• Most animals have an alimentary canal
running from mouth to anus, with specialized
regions
– Mouth: entrance for food
– Pharynx: throat; receives food
– Esophagus: channels food
– Crop: stores food
– Stomach, gizzard: churn and grind food
– Intestine: locus of chemical digestion and
absorption
– Anus: expels food
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LE 21-3b
Mouth
Pharynx
Esophagus
Crop
Gizzard
Anus
Intestine
Dorsal fold
Earthworm
Interior of intestine
Wall of intestine
Esophagus
Stomach
Anus
Mouth
Crop
Grasshopper
Gastric
pouches
Intestine
Stomach
Gizzard
Intestine
Mouth
Esophagus
Crop
Anus
Bird
Video: Hydra Eating Daphnia (time lapse)
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HUMAN DIGESTIVE SYSTEM
21.4 The human digestive system consists of an
alimentary canal and accessory glands
• Digestive glands secrete digestive juices that
enter the alimentary canal through ducts
– Salivary glands, pancreas, liver
• Muscles propel food through the alimentary
canal by rhythmic contractions (peristalsis)
• Pyloric sphincter regulates passage of food out
of stomach and into small intestine
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LE 21-4
Oral
cavity
Tongue
Mouth
Pharynx
Salivary
glands
Esophagus
Liver
Esophagus
Constriction
Stomach
Gallbladder
Pyloric
sphincter
Pancreas
Small
intestine
Large
intestine
Rectum
Anus
Small
intestine
21.5 Digestion begins in the oral cavity
• Teeth break up food
• Salivary glands secrete saliva
– Saliva protects lining of mouth and
lubricates food
– Salivary enzymes begin the hydrolysis of
starch
• Tongue
– Forms chewed food into bolus and pushes
bolus into the pharynx
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LE 21-5
Teeth
Incisors
Canine
Premolars
Molars
Tongue
Salivary
glands
Opening of a
salivary gland duct
21.6 The food and breathing passages both open
into the pharynx
• Most of the time, the esophageal opening is
closed, and air enters the trachea
• Food entering the pharynx triggers the
swallowing reflex
– Esophageal sphincter relaxes, letting food
enter
– Larynx closes the tracheal opening
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LE 21-6-3
Tongue
Bolus of food
Pharynx
Epiglottis
up
Esophageal
sphincter
Larynx
Trachea (windpipe)
Sphincter contracted
Epiglottis
down
Epiglottis
up
Larynx
up
Esophagus
Esophagus
Sphincter relaxed
Larynx
down
Sphincter contracted
CONNECTION
21.7 The Heimlich maneuver can save lives
• The Heimlich maneuver can dislodge food
from the pharynx or trachea during choking
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LE 21-7
save a CHOKING victim
HEIMLICH MANEUVER
It could save your life!
A choking person can’t speak or breathe and needs your help now.
Don’t slap the victim’s back. (This could make matters worse.)
Follow these 4 steps to clear the
blocked airway safely and quickly:
1.
From behind, wrap your
arms around the victim’s
waist.
2.
Make a fist and place the
thumb side of your fist
against the victim’s
abdomen, below the rib
cage and above the navel.
3.
Grasp your fist with your
other hand and press into
the victim’s abdomen with
a quick upward thrust.
4.
Repeat until object is
expelled.
®
21.8 The esophagus squeezes food along to the
stomach by peristalsis
• Muscles at the top of the esophagus begin the
act of swallowing voluntarily
• Involuntary contractions by smooth muscle in
the rest of the esophagus-peristalsis-move
food into the stomach
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LE 21-8
Muscles contract
Bolus of
food
Muscles
contract,
constricting
passageway
and pushing
bolus down
Muscles relax
Muscles relax,
allowing
passageway
to open
Stomach
Muscles contract
Muscles
relax
21.9 The stomach stores food and breaks it down with
acid and enzymes
•
The stomach surface is highly folded and dotted with
pits leading to gastric glands
•
Gastric glands secrete three components of gastric
juice
– Mucus lubricates and protects stomach lining
– Pepsinogen, an inactive form of the digestive
enzyme pepsin
– Hydrochloric acid converts pepsinogen to pepsin
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• Secretions of gastric glands are regulated by a
combination of nerve signals and hormones
– Presence of food stimulates secretion of
gastric juice
– Negative feedback inhibits secretion of
gastric juice when stomach contents are too
acidic
• Stomach contents are mixed by churning
action of muscles in stomach wall
– Food becomes nutrient-rich acid chyme
– Pyloric sphincter helps regulate passage of
acid chyme into small intestine
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Lumen
(cavity)
of stomach
Colorized SEM 2,500
LE 21-9
Interior surface
of stomach
Pits
Food
particle
Release of
gastric
juice
Release of juice
(mucus, HCl, and
pepsinogen)
Epithelium
Pepsinogen
Mucous
cells
Stomach
Pyloric
sphincter
Gastric
gland
Chief cells
Parietal cells
Pepsin
(active
HCl enzyme)
CONNECTION
21.10 Bacterial infections can cause ulcers
• Mucus normally protects the stomach wall from
the corrosive effects of digestive juice
• When it fails, gastric ulcers can develop
– Infection by the bacteria Heliobacter pilori
results in localized loss of mucus
– Pepsin and hydrochloric acid destroy cells
faster than they can regenerate
• The duodenum and esophagus are also
susceptible to ulcers
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LE 21-10
Bacteria
Colorized SEM 10,000
Mucous
layer of
stomach
21.11 The small intestine is the major organ of
chemical digestion and nutrient absorption
• Most chemical digestion of macromolecules
takes place in the small intestine, aided by
other organs
– Pancreas produces alkaline pancreatic juice
• Neutralizes the acid chyme
• Contains digestive enzymes
– Liver produces bile
• Emulsifies fat for attack by enzymes
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– Gallbladder stores bile
– Acid chyme from stomach mixes with bile,
pancreatic juice, and digestive enzymes in
the duodenum of the small intestine
• All four types of macromolecules are digested
in the small intestine by a variety of enzymes
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LE 21-11a
Liver
Bile
Gallbladder
Stomach
Bile
Acid chyme
Intestinal enzymes
Duodenum of
small intestine
Pancreatic
juice
Pancreas
• The small intestine has a huge surface area,
resulting from folds and projections
– Fingerlike villi, with surface microvilli,
contain lymph vessels and capillaries
• Nutrients are absorbed into the epithelium and
pass to blood or lymph
– Fatty acids and glycerol are first combined
into fats; other nutrients leave unprocessed
• Nutrients in blood flow to the liver, where they
are processed and stored
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LE 21-11b
Lumen of intestine
Nutrient
absorption
Vein
with blood
en route to
the liver
Nutrient absorption
into epithelial cells
Microvilli
Epithelial
cells
Muscle
layers
Amino
acids
and
sugars
Lumen
Fats
Blood
capillaries
Large
circular folds
Blood
Villi
Lymph
vessel
Lymph
Nutrient
absorption
Epithelial cells
Villi
Intestinal wall
Fatty
acids
and
glycerol
21.12 The large intestine reclaims water and
compacts the feces
• The large intestine, or colon, is about 1.5 m
long, joined to the small intestine by a
sphincter
– Appendix is a small extension of the cecum
• The main function of the large intestine is to
reabsorb water from undigested material
• Feces, the waste products of digestion, are
stored in the rectum along with prokaryotes
– E. Coli produce important vitamins
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 21-12
Large
intestine
(colon)
Small
intestine
Sphincter
End
of small
intestine
Rectum
Anus
Nutrient
flow
Appendix
Cecum
DIETS AND DIGESTIVE ADAPTATIONS
21.13 Adaptations of vertebrate digestive
systems reflect diet
• Herbivores and omnivores have longer
alimentary canals than carnivores
– Allow more time and surface area for
digesting plant material
• Most herbivores also have special chambers
containing cellulose-digesting microbes
• Some herbivores obtain more nutrients by
eating their feces
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LE 21-13a
Small
intestine
Small
intestine
Stomach
Cecum
Colon
(large
Intestine)
Carnivore
Herbivore
• Ruminant mammals have an elaborate system
for digesting cellulose
– Four-chambered stomach containing
microbes
– Cud-chewing
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LE 21-13b
Intestine
Omasum
Rumen
Esophagus
Rumen
Abomasum
Reticulum
NUTRITION
21.14 Overview: A healthful diet satisfies three
needs
• A healthy diet provides
– Fuel for an organism's activities
– Raw materials for biosynthesis
– Essential nutrients the animal cannot make
itself
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21.15 Chemical energy powers the body
• Every activity requires fuel in the form of
chemical energy
• Nutrients are oxidized by cellular metabolism
to generate energy in the form of ATP
• The energy content of food is measured in
kilocalories
– Basal metabolic rate: number of kilocalories
a resting animal needs to fuel only basic
body functions
• Excess kilocalories are stored as glycogen or
fat
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21.16 An animal's diet must supply essential nutrients
•
Essential nutrients are those that an animal must
obtain from its diet
– Essential fatty acids, essential amino acids,
vitamins, and minerals
– Animal's cells cannot make them from any raw
materials
•
Undernourishment: chronic deficiency of calories
•
Malnourishment: lacking one or more essential
nutrients
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CONNECTION
21.17 Vegetarians must be sure to obtain all
eight essential amino acids
• The eight essential amino acids can be
obtained from the proper combination of plant
foods
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LE 21-17
Essential
amino acids
Methionine
Valine
(Histidine)
Threonine
Phenylalanine
Leucine
Corn
Isoleucine
Tryptophan
Lysine
Beans and
other
legumes
21.18 A healthy diet includes 13 vitamins
• A vitamin is an organic nutrient required in
small quantities
– Must be obtained from diet
• Most vitamins function as coenzymes
– Absolutely necessary for healthy body
functioning
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21.19 Essential minerals are required for many
body functions
• Minerals are inorganic nutrients required in
small amounts
– Must be obtained from diet
– Play a variety of crucial roles in body
functioning
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CONNECTION
21.20 Do you need to take vitamin and mineral
supplements?
• A healthy diet usually contains enough
vitamins and minerals to meet the Minimum
Dietary Allowances
– Quantities are the subject of much debate
– Supplements ensure a sufficient quantity if
they are not obtained through diet
• Megadoses may be dangerous
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CONNECTION
21.21 What do food labels tell us?
• Food labels provide nutritional information
– Ingredients, in order by amount (greatest
first)
– Energy content (calories)
– Selected nutrients and daily values
• Emphasis on nutrients that are of health
concern
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LE 21-21
Ingredients: whole wheat flour,
water, high fructose corn syrup,
wheat gluten, soybean or canola oil,
molasses, yeast, salt, cultured whey,
vinegar, soy flour, calcium sulfate
(source of calcium).
CONNECTION
21.22 Obesity is a human health problem
• The World Health Organization has recognized
obesity as a global health problem
– Contributes to a number of serious diseases
– Caused by sedentary lifestyle, fattening
foods
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• Researchers have studied the genetic basis of
obesity
– Inheritance is one factor
– Many genes code for weight-regulating
hormones
• A defect in the gene for the appetite
regulator leptin, produced by adipose cells,
causes obesity in mice
• Function of leptin in humans is not clear
• In our feast-or-famine evolutionary past,
natural selection may have favored genes for
fat storage
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CONNECTION
21.23 What are the health risks and benefits of
fad diets?
• The effectiveness and health benefits of any
diet are tied to how weight loss occurs
– Low-carb diets
• Quick weight loss
• Lost weight quickly regained
• Reduce intake of vitamins, minerals, and
fiber
• Fatty foods may contribute to disease
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– Low-fat diets
• Healthy diet requires some fat
• Often lack adequate protein and fatty acids
• The body requires a balance of nutrients for
good health and long-term weight control
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CONNECTION
21.24 Diet can influence cardiovascular disease
and cancer
• Diet plays an important part in risk for disease
• Cardiovascular disease is linked to diets high
in saturated fats
– Found in animal products, hydrogenated
fats
– Trans fats produced by hydrogenated fats
– Correlate with high levels of cholesterol
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LE 21-24
Behavioral
risk factors
High blood cholesterol
and high blood
pressure
Unavoidable
risk factors
• Fatty diet
• Aging
• Lack of
exercise
• Family
history
• Smoking
Cardiovascular
disease
• Being
male
• Cholesterol travels through the body in blood
lipoproteins
– Low-density lipoproteins (LDLs) correlate
with blocked blood vessels, high blood
pressure, heart attacks
• Increased by diet high in saturated fats
– High-density lipoproteins (HDLs) may
decrease risk of vessel blockage
• Increased by exercise; decreased by
smoking
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• Diet seems to be involved in some forms of
cancer
– High levels of dietary fat and low levels of
dietary fiber may be linked to cancer
– Antioxidants may help prevent cancer
• Help protect cells from damaging free
radicals
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