Download PowerPoint lecture - Lower Cape May Regional School District

Chapter 39
Digestion and
Nutrition
Albia Dugger • Miami Dade College
39.1 Your Microbial “Organ”
• 10 trillion or more individual microorganisms reside in your gut
and affect your health
• More than half of the human population has the bacterium
Helicobacter pylori, which can cause peptic ulcers
• Low numbers of the bacterium Bifidobacterium in the gut may
be associated with irritable bowel syndrome (IBS)
• Researchers are studying the effectiveness of probiotics as
a treatment for some disorders
Helicobacter pylori
39.2 The Nature of Digestive Systems
• Digestive system
• A body cavity or tube that mechanically and chemically
breaks food down to small particles, then to molecules that
can be absorbed into the internal environment
Incomplete and Complete
Digestive Systems
• Incomplete digestive system
• A saclike gut with one opening in the body surface for food
to enter and waste to leave
• Complete digestive system
• A tubular gut with an opening at both ends
• Includes mouth, pharynx, esophagus, stomach, small and
large intestines, and anus
Incomplete Digestive System
branching saclike gut
A Incomplete digestive
system of a flatworm.
pharynx
single opening takes in
food, expels waste
Complete Digestive System: Frog
pharynx
esophagus
stomach
mouth
with
tongue
liver
gallbladder
pancreas
B Complete digestive
system of a frog.
small intestine
large intestine
cloaca (opening
through which
digestive wastes,
urinary wastes,
and gametes exit
the body)
Complete Digestive System: Bird
beak
mouth
esophagus
crop
glandular part
of stomach
gizzard
intestines
cloaca
ANIMATED FIGURE: Examples of digestive
systems
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE
Five Functions of
a Complete Digestive System
1. Mechanical processing and motility
2. Secretion of digestive enzymes into the lumen
3. Digestion of food into absorbable molecules
4. Absorption of nutrients into extracellular fluid
5. Elimination of solid residues
Diet-Related Structural Adaptations
• Bird adaptations
• Size and shape of beaks adapted to different diets
• Crops and gizzards
• Mammal adaptations
• Teeth adapted to different diets
• Multiple stomach chambers in ruminants
• Carnivores have a shorter gut than grazers
gumline
crown
root
antelope molar
crown
root
human molar
Figure 39-3a p697
ingestion, regurgitation, reswallowing
of food through esophagus
stomach
chamber 1
stomach
chamber 2
stomach
chamber 3
stomach
chamber 4
to small
intestine
Figure 39-3b p697
ANIMATED FIGURE: Antelope stomach
function
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE
Carnivore Stomach
Take-Home Message: How does digestive
system structure reflect function?
• Digestive systems mechanically and chemically degrade food
into small molecules that can be absorbed, along with water,
into the internal environment. These systems also expel the
undigested residues from the body.
• Incomplete digestive systems are a saclike cavity with one
opening. Complete digestive systems are a tube with two
openings and regional specializations in between.
• Structural variations in bills, teeth, and regions of the gut are
adaptations that allow an animal to exploit a particular type or
types of foods.
39.3 Overview of
the Human Digestive System
• Humans have a complete digestive system lined with mucuscovered epithelium
• Accessory organs such as salivary glands, pancreas, liver,
and gallbladder secrete enzymes and other substances that
aid in the breakdown of food and absorption of nutrients
From Mouth to Stomach
• Food is partially digested in the mouth and forced into the
pharynx by swallowing
• Food is moved through the esophagus by peristalsis
through a sphincter to the stomach, which adds acids and
enzymes to food and mixes them together
Gastrointestinal Tract
• The gastrointestinal tract starts at the stomach and extends
through the intestines to the terminal opening
• In the small intestine, carbohydrates, lipids and proteins are
digested by secretions from liver and pancreas; nutrients and
water are absorbed
• The large intestine absorbs water and ions, and compacts
wastes, which collect in the rectum, and are expelled from
the anus
Major Organs
Mouth
Accessory Organs
Salivary Glands
Pharynx (throat)
Esophagus
Liver
Stomach
Gallbladder
Pancreas
Small Intestine
Large Intestine
(colon)
Rectum
Anus
Figure 39-5 p698
ANIMATED FIGURE: Human digestive
system
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE
Take-Home Message: What type of digestive
system do humans have?
• Humans have a complete digestive system with a tubular,
mucosa-lined gut.
• Accessory organs positioned adjacent to the gut secrete
substances into its interior. These substances aid in digestion
of food or absorption of nutrients.
39.4 Digestion in the Mouth
• Digestion begins when teeth mechanically break down food
into smaller bits
• Teeth consist mostly of bonelike dentin; the crown is covered
by a hard layer of enamel
• Salivary amylase secreted by salivary glands begins the
breakdown of starch
molars
(12)
premolars
(8)
canines (4)
incisors
(8)
lower jaw
upper jaw
Figure 39-6a p699
enamel
dentin
crown
pulp cavity
(contains
nerves and
blood vessels)
gingiva
(gum)
ligaments
root
root canal
periodontal
membrane
bone
Figure 39-6b p699
Take-Home Message:
What happens to food in the mouth?
• Teeth mechanically break food into smaller particles.
Enzymes in saliva begin the chemical digestion of
carbohydrates.
3D ANIMATION: Swallowing
39.5 Food Storage and
Digestion in the Stomach
• The stomach is a muscular, stretchable sac with a sphincter
at either end
• The stomach has three digestive functions:
• Stores food and controls the rate of passage to the small
intestine
• Mechanically mixes and breaks down food
• Secretes substances used in chemical digestion
gastroesophageal
sphincter
esophagus
serosa
longitudinal
muscle
pyloric sphincter
circular
muscle
oblique
muscle
submucosa
small intestine
mucosa
Figure 39-7 p700
Digestion in the Stomach
• Stomach mucosa secretes gastric fluid containing
hydrochloric acid and enzymes that begin protein digestion
• Gastrin signals secretion of acid and pepsinogens
• Acid unfolds proteins
• Pepsin breaks proteins into peptides
• Chyme passes into the small intestine
Take-Home Message:
What are the functions of the stomach?
• The stomach receives food from the esophagus and stretches
to store it.
• Contractions of stomach muscles break up food and mix it
with acidic gastric fluid. They also move the resulting mixture
(the chyme) into the small intestine.
• Chemical digestion of proteins begins in the stomach.
ANIMATION: Digestion in mammalian
stomachs
39.6 Structure of the Small Intestine
• The small intestine has a highly folded lining with many
projections that make its surface area enormous
• Most digestion and absorption take place at the surface of the
small intestine
Epithelium of the Small Intestine
• Many folds and projections of the small intestinal lining
increase its surface area for absorption
• Multicelled, fingerlike absorptive structures (villi) with lymph
and blood vessels extend from folds
• Brush border cells at the surface have membrane
extensions (microvilli) that project into the lumen
Function of Brush Border Cells
• Brush border cells function in both digestion and absorption
• Digestive enzymes at the surface of a microvillus break down
sugars, protein fragments, and nucleotides
• Many transport proteins facilitate the movement of nutrients
into the microvillus
A Longitudinal cross section through the
small intestine showing its folded lining.
Figure 39-8a p701
villi
blood
vessels
lymph
vessel
B Intestinal fold with
villi at its surface.
C One villus with
brush border cells
at its surface.
Figure 39-8bcde p701
time
Figure 39-9 p701
Take-Home Message:
Small intestine structure and function
• The surface of the small intestine is highly folded and each
fold has many projections (villi). Brush border cells at the
surface of a villus have tiny projections (microvilli) at their
surface.
• The many folds and projections greatly increase the surface
area for the two functions of the small intestine—digestion
and absorption.
39.7 Digestion in the Small Intestine
• In the small intestine, chyme mixes with secretions from the
pancreas and liver
• Pancreatic enzymes break down larger molecules into units
that can be absorbed
• Monosaccharides, monoglycerides, fatty acids, amino
acids, nucleotides, nucleotide bases
• Bicarbonate from the pancreas buffers acids so enzymes
can work
Carbohydrate Digestion and Absorption
• In the mouth, salivary amylase broke polysaccharides into
disaccharides
• In the small intestine, pancreatic amylase breaks down
polysaccharides
• Enzymes embedded in the plasma membrane of the brush
border cells split disaccharides into monosaccharide
• Monosaccharides are actively transported into a brush border
cell, then into interstitial fluid inside a villus, then enter blood
Protein Digestion and Absorption
• Protein digestion began in the stomach, where pepsin broke
proteins into polypeptides
• The small intestine releases cholecystokinin (CCK) into the
blood, which causes the pancreas to secrete proteases such
as trypsin and chymotrypsin into the small intestine
• Enzymes at the surface of brush border cell break peptide
fragments into amino acids, which are actively transported
into brush border cells, interstitial fluid, and blood
Fat Digestion
• Lipid (fat) digestion in the small intestine requires enzymes
and bile, which is produced by the liver and stored in the
gallbladder
• Bile is a mixture of salts, pigments, cholesterol and lipids that
emulsifies fats into small drops that enzymes can break
down into fatty acids and monoglycerides
Fat Absorption
• Fatty acids and monoglycerides combine with bile salts to
form micelles, which aid diffusion into brush border cells (bile
salts stay in lumen)
• In brush border cells, fatty acids and monoglycerides combine
with proteins to form lipoproteins, which enter the villus by
exocytosis
• From interstitial fluid, triglycerides enter lymph vessels, which
empty into the bloodstream
Fluid Absorption
• Transport proteins move salts, sugars, and amino acids from
the intestinal lumen, into brush border cells, then into
interstitial fluid in a villus
• Water follows the solutes by osmotic gradient
• Capillaries in the villus distribute water and solutes through
the body
Table 39-1 p702
1
carbohydrates
3 proteins
monosaccharides
fat globules
(triglycerides)
+
bile salts
amino acids
2
Lumen of Small Intestine
5 emulsification
droplets
6
free fatty acids,
monoglycerides + bile salts
7
4
Brush
Border
Cell
triglycerides + proteins
lipoproteins
8
Internal Environment
(interstitial fluid inside a villus)
Stepped Art
Figure 39-10a p703
ANIMATED FIGURE: Digestion and
absorption in the small intestine
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE
Take-Home Message:
What are the roles of the small intestine?
• Chemical digestion is completed in the small intestine.
Enzymes from the pancreas and enzymes embedded in the
membrane of brush border cells break large molecules into
smaller, absorbable subunits.
• Small subunits (monosaccharides, amino acids, fatty acids,
and monoglycerides) enter the internal environment when
they are absorbed into the interstitial fluid in a villus.
• Most fluid that enters the gut is also absorbed across the wall
of the small intestine.
39.8 The Large Intestine
• The large intestine is wider than the small intestine, but also
much shorter—only about 1.5 meters (5 feet) long
• The ascending colon begins at the cecum, where the
appendix is attached
• The descending colon attaches to the rectum
Function of the Large Intestine
• The large intestine completes the process of absorption, then
concentrates wastes, and compacts them as feces
• Bacteria in the colon make vitamin B12, which is absorbed
through the colon lining
• Stretch receptors in the rectum trigger the defecation reflex
Disorders of the Large Intestine
• Stress, a diet low in fiber, minimal exercise, dehydration, and
some medications can lead to constipation
• Diarrhea may result from a bacterial infection, and cause
dehydration
• Appendicitis must be treated to prevent rupture and infection
of the abdominal cavity
• Colon polyps leading to cancer can be detected and removed
by colonoscopy
ascending
colon
cecum
appendix
last
portion
of small
intestine
Figure 39-11 p704
colon polyp
transverse colon
descending colon
Figure 39-11 p704
Take-Home Message:
What is the function of the colon?
• The colon completes the process of absorption, then
concentrates, stores, and eliminates wastes.
39.9 Metabolism of
Absorbed Organic Compounds
• Absorbed compounds are carried by the blood to the liver,
which plays a central role in metabolism
• Most absorbed compounds are broken down for energy,
stored, or used to build larger compounds
• Excess carbohydrates and proteins are converted to fat and
stored in adipose tissue
FOOD INTAKE
dietary carbohydrates, lipids
dietary proteins, amino acids
Cytoplasmic Pool
of Carbohydrates, Fats
(interconvertible forms)
Cytoplasmic Pool
of Amino Acids
ammonia
storage
forms
(e.g.,
glycogen)
building
blocks for
cell
structures
specialized
derivatives
(e.g., steroids,
acetylcholine)
instant
energy
sources
for cells
urea
excreted
in urine
nitrogencontaining
derivatives
(e.g., hormones,
nucleotides)
building
blocks for
structural
proteins,
enzymes
Stepped Art
Figure 39-12 p705
Liver Function
• The liver detoxifies dangerous substances (alcohol, NH3), and
stores fat-soluble vitamins (A, D) and glucose (as glycogen)
• Between meals, the liver provides the brain with glucose by
breaking down stored glycogen
Liver Function
Take-Home Message: What happens to
compounds absorbed from the gut?
• Blood carries the absorbed compounds to the liver, which
detoxifies dangerous substances and stores vitamins and
glucose. The glucose is stored as glycogen.
• Adipose tissue takes up absorbed carbohydrates and proteins
and converts them to fats.
•
In between meals, the liver breaks down stored glycogen,
and releases its glucose subunits into the blood. This ensures
that the brain, which can only use carbohydrates as fuel,
always has an adequate supply of energy.
39.10 Human Nutritional Requirements
• Diet profoundly affects your body’s structure and function
• Eating provides your cells with a source of energy and a
supply of essential building materials
USDA Dietary Recommendations
• The USDA reviews research on human nutrition and issues a
set of dietary guidelines
• Current guidelines recommend eating less refined grains,
saturated fats, trans fatty acids, sugar or caloric sweeteners,
and salt – and more vegetables and fruits, whole grains, and
fat-free or lowfat milk products
• Guidelines based on age, sex, height, weight, and activity
level can be generated online at www.ChoseMyPlate.gov
Sample USDA Nutritional Guidelines
Energy-Rich Carbohydrates
• Good (complex) carbohydrates provide energy, vitamins, and
fiber (soluble and insoluble)
• Fresh fruits, whole grains, and vegetables
• Not so good (processed) carbohydrates have “empty
calories”
• White flour, refined sugar, corn syrup
Good Fat, Bad Fat
• Lipids are used in cell membranes (phospholipids and
cholesterol), as energy reserves, insulation and cushioning,
and to store fat-soluble vitamins
• Essential fatty acids (linoleic and alpha-linoleic acids) must
be obtained from the diet
Good Fat, Bad Fat
• Unsaturated fats are liquid at room temperature
• Polyunsaturated fats (such as omega-3 fatty acids) and
monounsaturated fats (such as oleic acid) have specific
health benefits
• Saturated fats (in meat and dairy products) can increase risk
of heart disease, stroke, or cancer
• Trans fats are worse than saturated fats
Table 39-2 p706
Food Labels Now Show Trans Fats
Body-Building Proteins
• Proteins are the source of amino acids used to build all body
proteins
• Meat provides all eight essential amino acids
• Most plant foods lack one or more amino acids, but can meet
all human amino-acid needs when combined correctly
Take-Home Message: What are the main types
of nutrients that humans require?
• A healthy diet provides energy and all necessary building
blocks for assembling essential body components.
• Nutritional guidelines are periodically revised in light of new
research. Current guidelines call for most calories to come
from complex carbohydrates, rather than simple sugars. They
also favor fat and protein sources that are low in saturated
and trans fats.
• A person can obtain all the required nutrients from a
vegetarian diet, but doing so requires combining plant foods
so amino acids lacking in one are present in the other.
39.11 Vitamins, Minerals,
and Phytochemicals
• Vitamins
• Organic substances that are essential in very small
amounts in the diet (coenzymes)
• Minerals
• Inorganic substances with essential metabolic functions
(such as iron in hemoglobin)
• Phytochemicals
• Beneficial organic molecules found in plant foods
Table 39-3 p708
Table 39-4 p709
Take-Home Message: What roles do vitamins,
minerals, and phytonutrients play?
• Vitamins are organic molecules with an essential role in
metabolism.
• Minerals are inorganic substances with an essential role.
• Phytochemicals are plant molecules that are not essential but
may reduce the risk of certain disorders.
39.12 Maintaining a Healthy Weight
• Body mass index (BMI) estimates health risks
• Overweight: 25 to 29.9
• Obese: 30 or more
BMI = [weight (lbs) x 703] ÷ height (in)2
Maintaining Your Preferred Weight
• To calculate how many kilocalories you need, multiply your
weight in pounds by 10 (if you are not active), or by 15
(moderately active), or by 20 (highly active)
• Subtract one of the following amounts:
• Age: 25–34; Subtract: 0
• 35–44; 100
• 45–54; 200
• 55–64; 300
• Over 65; 400
Why Is Obesity Unhealthy?
• Being overweight increases health risks:
• Type 2 diabetes, high blood pressure, heart disease,
breast and colon cancer, arthritis, gallstones
• An unhealthy overabundance of fat (obesity) stresses fat
cells, triggers inflammatory response
• Fat cells do not increase in number after birth
• Excess weight overfills existing fat cells
Genetics of Obesity
• Genetic factors influence how difficult it is for a person to
reach and maintain a healthy weight
• The ob gene encodes leptin, a hormone made by adipose
cells, which acts in the brain and suppresses appetite
• About 16% of people of European ancestry are homozygous
for an fto allele that predisposes them to obesity
Effect of the Hormone Leptin
Eating Too Little
• With anorexia nervosa, a person who has access to food
routinely eats too little to maintain a normal weight
• Most affected people see themselves as fat, even when they
are dangerously thin
• Anorexia damages organ systems throughout the body and
can result in death from sudden cardiac arrest
• People with bulimia nervosa, “binge and purge,” which can
shift pH, resulting in abnormal heart rhythm and convulsions
Take-Home Message:
How does weight affect health?
• A person who balances caloric intake with energy
expenditures will maintain current weight.
• Obesity raises the risk of heart disease, type 2 diabetes,
some cancers, and other disorders. These problems may
arise because overstuffed adipose cells summon up
inflammatory responses in organs throughout the body.
• Anorexia is an eating disorder that results in a lower than
normal body weight. It harms organs throughout the body,
especially the bones and the heart. Anorexia-induced
changes in heart rhythms can be fatal.