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CHAPTER 21 Nutrition and Digestion
c. Absorption is the take up of the
products of digestion, usually by
the cells lining the digestive tract.
d. Elimination is the removal of undigested materials out of the digestive tract.
C. 21.3 Digestion occurs in specialized
compartments
1. Sponges digest food in vacuoles.
2. Most animals digest food in compartments.
3. Cnidarians and flatworms have a
gastrovascular cavity with a single
opening, the mouth.
a. Food enters the mouth.
b. Enzymes break down the food.
c. Food particles move into cells lining the compartment.
d. Undigested materials are expelled
back out the mouth.
4. Most animals have an alimentary
canal with
a. a mouth,
b. an anus, and
c. specialized regions associated
with one-way flow of food.
5. The normal one-way flow moves
food
a. into the pharynx or throat,
b. down the esophagus to a
i. crop where food is softened
and stored,
ii. gizzard, where food is ground
and stored, and/or
iii. mach where food is ground
and stored,
c. to the intestines, where chemical
digestion and nutrient absorption
occur, and
finally
d. undigested materials are expelled
through the anus.
Lecture Outline
I. Introduction
A. All animals must eat to provide
1. energy and
2. the building blocks used to assemble
new molecules.
B. Animals also need essential
1. vitamins and
2. minerals.
C. The modern human diet in developed
countries allows access to relatively
cheap and available calorie-dense
foods.
D. This diet, combined with sedentary jobs
and inactive lifestyles, has led to an
obesity crisis in the United States leading to
1. 68% of people categorized as overweight and
2. 100 million people categorized as
obese.
E. Thus, the modern diet appears to be
contributing to shorter, less healthy
lives.
II. Obtaining and Processing Food
A. 21.1 Animals obtain and ingest their
food in a variety of ways
1. Most animals have one of three
kinds of diets.
a. Herbivores eat plants and include
cattle, snails, and sea urchins.
b. Carnivores eat meat and include
lions, hawks, and spiders.
c. Omnivores eat plants and other
animals and include humans,
roaches, raccoons, and crows.
2. Animals obtain and ingest their food
in different ways.
a. Suspension feeders sift small
organisms or food particles from
water.
b. Substrate feeders live in or on
their food source and eat their way
through it.
c. Fluid feeders suck nutrient-rich
fluids from a living host.
d. Bulk feeders ingest large pieces
of food.
B. 21.2 Overview: Food processing occurs
in four stages
1. Food is processed in four stages.
a. Ingestion is the act of eating.
b. Digestion is the breaking down of
food into molecules small enough
for the body to absorb.
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III.
The Human Digestive System
A. 21.4 The human digestive system consists of an alimentary canal and accessory glands
1. In humans, food is
a. ingested and chewed in the mouth
or oral cavity,
b. pushed by the tongue into the
pharynx,
c. moved along by alternating waves
of contraction and relaxation by
smooth muscle in the walls of the
canal in a process called peristalsis, and
d. moved in and out of the stomach
by sphincters.
Copyright © 2012 Pearson Education, Inc.
B.
C.
D.
E.
F.
e. The final steps of digestion and
nutrient absorption in humans occur in the small
intestine.
f. Undigested materials move
through the large intestine, feces
are stored in the
rectum, and then expelled out the
anus.
21.5 Digestion begins in the oral cavity
1. Mechanical and chemical digestion
begin in the mouth.
2. Chewing cuts, smashes, and grinds
food, making it easier to swallow.
3. The tongue
a. tastes,
b. shapes the food into a ball called
a bolus, and
c. moves it toward the pharynx.
Salivary glands release
1. a slippery glycoprotein that moistens
and lubricates food for easier swallowing,
2. buffers that neutralize acids,
3. salivary enzyme amylase that begins
the hydrolysis of starch, and
4. antibacterial agents that kill some
bacteria ingested with food.
21.6 After swallowing, peristalsis moves
food through the esophagus to the
stomach
1. Air moves from the pharynx,
a. into the larynx,
b. past the vocal cords in the voice
box,
c. into the trachea, and
d. into the lungs.
2. Swallowed food and drink move from
the pharynx,
a. into the esophagus, and
b. into the stomach.
3. During swallowing,
a. the tip of the larynx moves upward,
b. preventing the food from entering
the trachea.
21.7 CONNECTION: The Heimlich maneuver can save lives
1. The Heimlich maneuver
a. involves a forceful elevation of the
diaphragm,
b. pushes air into the trachea, and
c. can dislodge food from the pharynx or trachea during choking.
2. Brain damage will occur within
minutes if no airway is open.
21.8 The stomach stores food and
breaks it down with acid and enzymes
1. The stomach can stretch and store
up to 2 liters of food and drink.
2. Some chemical digestion occurs in
the stomach.
3. The stomach secretes gastric juice,
made up of
a. mucus,
b. a protein-digesting enzyme, and
c. strong acid with a pH of about 2
that
i. kills ingested bacteria,
ii. breaks apart cells in food, and
iii. denatures proteins.
4. Pepsinogen and HCl produce active
pepsin.
a. Pepsinogen, H+, and Cl– are secreted into the lumen of the stomach.
b. HCL converts some pepsinogen to
pepsin.
c. Pepsin helps activate more pepsinogen, starting a chain reaction.
d. Pepsin begins the chemical digestion of proteins.
5. What prevents the gastric juices from
digesting the walls of the stomach?
a. The secretion of pepsin in the inactive form of pepsinogen helps
protect the cells of the gastric
glands.
b. Mucus helps protect the stomach
lining against HCl and pepsin.
c. New cells lining the stomach are
produced about every three days
to those that have been damaged.
G. 21.9 CONNECTION: Digestive ailments
include acid reflux and gastric ulcers
1. Acid reflux of chyme in the stomach
back into the esophagus causes the
feeling of heartburn.
2. Gastroesophageal reflux disease
(GERD) results from frequent and
severe acid reflux that harms the lining of the esophagus.
3. Open sores in the lining of the stomach, called ulcers, may form.
4. Bacterial infections (Helicobacter pylori) in the stomach and duodenum
can produce ulcers.
H. 21.10 The small intestine is the major
organ of chemical digestion and nutrient
absorption
1. The small intestine is
a. named for its smaller diameter,
b. about 6 meters long,
c. the site of much chemical digestion, and
d. where most nutrients are absorbed.
2. The first 25 cm of the small intestine
is the duodenum, where chyme
squirted from the stomach mixes with
digestive juices from the pancreas,
liver, gallbladder, and gland cells in
the intestinal wall.
a. The pancreas produces pancreatic juice containing a mixture of digestive enzymes and an alkaline
solution rich in bicarbonate.
b. The liver produces bile, which is
stored in the gallbladder until it is
needed. Bile breaks up fats into
small droplets that are more susceptible to attack by digestive
enzymes.
c. The intestinal wall produces digestive enzymes.
3. The surface area for absorption in
the small intestine is greatly increased by
a. folds of the intestinal lining,
b. fingerlike projections called villi,
and
c. tiny projections of the surface of
intestinal cells called microvilli.
4. Nutrients pass into epithelial cells by
a. diffusion and
b. against concentration gradients.
5. Fatty acids and glycerol are
a. recombined into fats,
b. coated with proteins, and
c. transported into lymph vessels.
6. Other absorbed nutrients such as
amino acids and sugars pass
a. out of the intestinal epithelium,
b. across the thin walls of the capillaries into blood, and finally
c. to the liver.
I. 21.11 One of the liver’s many functions
is processing nutrient-laden blood from
the
intestines
1. Blood from the digestive tract drains
a. into the hepatic portal vein
b. to the liver.
2. The liver performs many functions.
The liver
a. converts glucose in blood to glycogen,
b. stores glycogen and releases
sugars back into the blood as
needed,
c. synthesizes many proteins including blood clotting proteins and lipoproteins that transport fats and
cholesterol to body cells,
d. modifies substances absorbed in
the digestive tract into less toxic
forms, and
e. produces bile.
J. 21.12 The large intestine reclaims water
and compacts the feces
1. The large intestine, or colon,
a. is about 1.5 m long and 5 cm in
diameter,
b. has a pouch called the cecum
near its junction with the small intestine, which bears a small fingerlike extension, the appendix,
c. contains large populations of E.
coli, which produce important vitamins,
d. absorbs these vitamins and water
into the bloodstream, and
e. helps form firm feces, which are
stored in the rectum until elimination.
2. Diarrhea occurs when too little water
is reclaimed from the contents of the
large
intestine.
3. Constipation occurs when too much
water is reclaimed.
K. 21.13 EVOLUTION CONNECTION:
Evolutionary adaptations of vertebrate
digestive systems relate to diet
1. The length of the digestive tract often
correlates with diet. In general, the
alimentary
canals relative to their body size are
a. longer in herbivores and omnivores and
b. shorter in carnivores.
2. Many herbivores have specializations of the gut that promote the
growth of cellulose-digesting bacteria
and protists because these animals
lack the enzymes needed to digest
cellulose in plants.
3. These mutualistic organisms may be
housed in
a. the cecum, in a coyote or koala,
b. the large intestine and the cecum
in rabbits and some rodents, or
c. the stomach of ruminants such
as cattle, sheep, and deer.
IV.
Nutrition
A. 21.14 Overview: An animal’s diet must
satisfy three needs
1. All animals have the same basic nutritional needs. Animals must obtain
a. fuel to power all body activities,
b. organic molecules to build the animal’s own molecules, and
c. essential nutrients, or substances
the animal cannot make for itself.
B. 21.15 Chemical energy powers the
body
1. Cellular respiration produces the
body’s energy currency, ATP,
a. by oxidizing organic molecules digested from food and
b. usually using carbohydrates or
fats as fuel.
2. A gram of fat has more than twice as
many calories as a gram of carbohydrate or
protein.
3. The energy content of food is measured in kilocalories (1 kcal = 1,000
calories).
4. Dietary calories are actually kilocalories and are written as Calories.
5. The rate of energy consumption by
an animal is called its metabolic
rate, the sum of all the energyrequiring biochemical reactions over
a given interval of time.
6. The basal metabolic rate (BMR) is
the energy a resting animal requires
each day.
7. The metabolic rate is the BMR plus
the energy needed for physical activity.
8. Excess energy is stored as glycogen
or fat.
C. 21.16 An animal’s diet must supply essential nutrients
1. Essential nutrients cannot be made
from any raw material.
2. There are four classes of essential
nutrients.
a. Essential fatty acids, such as
linoleic acid, are
i. used to make phospholipids of
cell membranes and
ii. found in seeds, grains, and
vegetables.
b. Essential amino acids are
i. used to make proteins and
ii. found in meats, eggs, and
milk.
c. Vitamins are organic nutrients
discussed in module 21.17.
d. Minerals are simple inorganic nutrients discussed in module 21.17.
3. Malnutrition is a chronic deficiency
in calories or one or more essential
nutrients. The most common type of
human malnutrition is protein deficiency.
4. Undernutrition occurs when
a. diets do not supply sufficient
chemical energy or
b. a person suffers from anorexia
nervosa or bulimia.
D. 21.17 A healthy human diet includes 13
vitamins and many essential minerals
1. Essential vitamins and minerals are
a. required in minute amounts and
b. absolutely essential to good
health.
2. Vitamins are organic nutrients that
may be
a. water-soluble, such as vitamins B
and C, or
b. fat-soluble, such as vitamins A, D,
E, and K.
3. Minerals are simple inorganic nutrients.
a. Calcium and phosphorus are required in larger amounts.
b. Iron is needed to make hemoglobin.
c. Iodine is required to make thyroid
hormones.
d. Most people ingest more salt than
they need.
4. The Recommended Dietary Allowances (RDAs) are
a. the minimum amounts of nutrients
that are needed each day and
b. determined by a national scientific
panel.
5. Overdoses of vitamins can be harmful.
a. In general, excess water-soluble
vitamins will be eliminated in
urine.
b. However, excess fat-soluble vitamins can accumulate to toxic levels in body fat.
E. 21.18 SCIENTIFIC DISCOVERY: Scientists use observations and experiments to determine nutritional needs
1. Many insights into human nutrition
have come from epidemiology, the
study of
human health and diseases within
populations.
a. The essential need for vitamin C
was revealed by the high incidence of scurvy in sailors on long
sea voyages.
b. The need for folic acid to prevent
neural tube defects in newborns
was revealed by studies of pregnant women of low socioeconomic
status. Since 1998, folic acid has
been added to foods such as
bread and cereals sold in the
United States.
F. 21.19 CONNECTION: Food labels provide nutritional information
1. Food labels indicate
a. serving size,
b. calories per serving,
c. amounts of selected nutrients per
serving and as a percentage of
daily value, and
d. recommendations for daily limits
of selected nutrients.
G. 21.20 EVOLUTION CONNECTION:
The human health problem of obesity
may reflect our evolutionary past
1. Overnourishment is the consumption
of more food energy than is needed
for normal
metabolism.
2. Obesity is the excessive accumulation of fat.
3. The World Health Organization recognizes obesity as a major global
health problem.
4. In the United States, the percentage
of obese people has doubled to more
than 30% in the past two decades.
More than 35% are overweight.
5. Weight problems often begin at a
young age.
a. 15% of children and adolescents
in the United States are obese.
b. Another 17% are overweight.
6. Obesity leads to
a. type 2 diabetes,
b. cancer of the colon and breasts,
and
c. cardiovascular disease.
7. Obesity is estimated to be a factor in
300,000 deaths per year in the United States.
8. A 15-year study published in 2010
indicates that obesity now surpasses
smoking in its contribution to disease
and the shortening of healthy life
spans.
9. The complexity of weight control in
humans is evident from studies of
the hormone leptin.
10. Leptin
a. is produced by adipose (fat) cells
and
b. suppresses appetite.
c. Obese children who have an inherited mutant form of the leptin
gene lose weight after leptin
treatments.
d. However, high levels in otherwise
healthy people do not suppress
appetite.
H. 21.21 CONNECTION: What are the
health risks and benefits of weight loss
plans?
1. Why are so many people overweight? Is it
a. lack of exercise,
b. the amount of food,
c. the quality of food, or
d. a combination of the above?
2. The U.S. market for weight loss
products and services has gone from
about $60
million a year in 1999 to more than
$48 billion a year today.
3. Weight loss diets may
a. help individuals lose weight but
b. have health risks leading to malnourishment.
4. Some severely obese individuals
may be candidates for weight-loss
surgery.
5. Scientific studies of weight-loss diets
indicate that the best way to lose
weight and keep it off is to
a. increase exercise and
b. eat a balanced diet with adequate
amounts of all essential nutrients.
I. 21.22 CONNECTION: Diet can influence risk of cardiovascular disease and
cancer
1. A healthy diet may reduce the risk of
a. cardiovascular disease and
b. cancer.
2. Two main types of cholesterol occur
in the blood.
a. Low-density lipoproteins (LDL)
contribute to
i. blocked blood vessels and
ii. higher blood pressure.
b. High-density lipoproteins (HDL)
help to reduce blocked blood vessels.
i. Exercise increases HDL levels.
ii. Smoking decreases HDL levels.
iii. Trans fats in the diet tend to
increase LDL levels.
iv. Eating mainly unsaturated fats
tends to lower LDL levels.
3. The relationship between food and
health is complex.
4. The American Cancer Society recommends
a. regular exercise and
b. a diverse diet of healthy foods with
an emphasis on plant sources.
Vocabulary to know
absorption
alimentary canal
anus
appendix
basal metabolic rate
(BMR)
bile
bolus
bulk feeders
carnivores
cecum
chyme
colon
crop
digestion
duodenum
elimination
esophagus
essential amino acids
essential fatty acids
essential nutrients
feces
fluid feeders
gallbladder
gastric juice
gastrin
gastrovascular cavity
gizzard
hepatic portal vein
herbivores
high-density
lipoproteins (HDLs)
ingestion
intestine
kilocalorie (kcal)
large intestine
liver
low-density
lipoproteins (LDLs)
malnutrition
metabolic rate
microvilli
mineral
mouth
obesity
omnivores
oral cavity
pancreas
peristalsis
pharynx
Recommended Dietary
Allowances (RDAs)
rectum
ruminants
salivary glands
small intestine
sphincter
stomach
substrate feeders
suspension feeders
villi
vitamin
Word Roots
carni- = flesh; -vora = eat (carnivore: an animal that mainly eats other animals)
chymo- = juice (chyme: the mixture of partially digested food and digestive juices formed in the stomach)
gastro- = stomach; -vascula = a little vessel (gastric juice: the collection of fluids [mucus,
enzymes, and acid] secreted by the stomach; gastrin: a digestive hormone that stimulates the
secretion of gastric juice; gastrovascular cavity: a central cavity in the body of certain animals that functions in
both the digestion and distribution of nutrients)
herb- = grass (herbivore: an animal that mainly eats plants or algae)
kilo- = thousand (kilocalorie: the quantity of heat equal to 1,000 calories, used to measure the
energy content of food, and usually referred to as a “calorie”)
micro- = small; -villi = shaggy hair (microvillus [plural, microvilli]: one of the many small, fingerlike microscopic
projections on the epithelial cells that serve to increase the surface area of the
lumen in the small intestine)
omni- = all (omnivore: an animal that consumes both meat and plant material)
peri- = around; -stalsis = a constriction (peristalsis: rhythmic waves of contraction of smooth muscle that push
food along the digestive tract)
villius- = shaggy hair (villus [plural, villi]: one of many fingerlike projections of the inner surface of the small intestine, which serve to increase surface area)
Name
Date
Class
Ch. 25 Study Guide: On a separate sheet of paper- Use the Chapter 25 Outline to construct a summary
for each of the following objectives by converting the appropriate information into paragraph form.
Opening Essay
Explain why obesity is increasing in the United States.
Obtaining and Processing Food
21.1 Define and distinguish between carnivores, herbivores, omnivores, suspension feeders, substrate
feeders, fluid feeders, and bulk feeders.
21.2 Describe the four stages of food processing. Explain how animals are protected against self-digestion.
21.3 Compare the structures and functions of a gastrovascular cavity and an alimentary canal. Describe
the specialized digestive systems of an earthworm, a grasshopper, and a bird.
Human Digestive System
21.4 Describe the main components of the human alimentary canal and the associated digestive glands.
21.5 Describe the functional components of saliva and the types and functions of the teeth in humans.
21.6 Explain how swallowing occurs and how food is directed away from the trachea.
21.7 Explain how the Heimlich maneuver is performed.
21.8 Relate the structure of the stomach to its functions. Describe the functions of the secretions of the
stomach. Finally, explain why the stomach does not digest itself.
21.9 Describe the causes and treatments of heartburn, GERD, and gastric ulcers.
21.10 Describe the different types of chemical digestion that occur in the small intestine. Explain how the
structure of the small intestine promotes nutrient absorption.
21.11 Explain how the liver helps to regulate the chemical composition of blood.
21.12 Describe the structures and functions of the colon and rectum. Note the causes of diarrhea and
constipation.
21.13 Compare the digestive tracts of carnivores and herbivores. Describe how the digestive tracts of a
koala and a coyote are specialized to digest cellulose.
21.13 Describe the process of ruminant digestion.
Nutrition
21.14
List the three nutritional needs common to all animals.
21.15
Define the basal metabolic rate. Explain how energy is obtained and stored in the body.
21.16
Describe the four classes of essential nutrients. Distinguish between undernutrition and alnutrition.
21.17
Define and distinguish between vitamins and minerals. Distinguish between water-soluble and fatsoluble vitamins. Define the essential minerals and explain why each is important in our diet.
21.17
Define the Recommended Dietary Allowances and explain how they contribute to good health.
21.18 Explain how scientists determine the levels of vitamins and minerals needed in the diet for good
health.
21.18 Explain why, since 1998, the United States has required the addition of folic acid to certain foods.
21.19 Describe the types of information found on food labels.
21.20 Describe the obesity epidemic in the United States. Describe the role of leptin in weight management.
Explain why cravings for fat may have once been adaptive.
21.21 Describe the best approach to weight control.
21.22 Explain how diet can influence the risks of cardiovascular disease and cancer.