Transcript Evolutionary Digestive Adaptations in Vertebrates

Evolutionary Digestive Adaptations in
Vertebrates
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Digestive systems of vertebrates are variations on a common
plan
However, there are intriguing adaptations, often related to
diet
Dentition, an animal’s assortment of teeth, is one example of
structural variation reflecting diet
Herbivores generally have longer alimentary canals than
carnivores, reflecting the longer time needed to digest
vegetation
Mutualistic Adaptations:
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Many herbivores have fermentation chambers, where symbiotic
microorganisms digest cellulose
The most elaborate adaptations for an herbivorous diet have
evolved in the animals called ruminants
Fig. 41-18
Incisors
Canines
(a) Carnivore
(b) Herbivore
(c) Omnivore
Premolars
Molars
Fig. 41-19
Small intestine
Stomach
Small
intestine
Cecum
Colon
(large
intestine)
Carnivore
Herbivore
Fig. 41-20
1
Rumen
2
Reticulum
Intestine
Esophagus
4
Abomasum
3
Omasum
Nutritional Aspects in Assimilation
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An animal’s diet provides chemical energy, which is
converted into ATP and powers processes in the
body
Animals need a source of organic carbon and
organic nitrogen in order to construct organic
molecules
Essential nutrients are required by cells and must
be obtained from dietary sources
Fig. 41-1
Nutrition: Carbohydrates
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Carbohydrates are present in food in the form of
sugars, starch, and fiber.
Fruits, vegetables, milk, and honey are natural
sources of sugars.
After being absorbed from the digestive tract all
sugars are converted to glucose
 Glucose
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is the preferred direct energy source in cells.
Plants store glucose as starch
Animals store glucose as glycogen
Nutrition: Proteins
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Adequate protein formation requires 20 different
types of amino acids
Adults require 8 from the diet, children require 9
 Essential
amino acids
 Some foods, such as meat, milk, and eggs, provide all
20 (complete)
 Vegetables supply one or more essential amino acids,
but are deficient in at least one
 Vegetarians should combine plant products to provide
all the essential amino acids
Fig. 41-2
Essential amino acids for adults
Methionine
Valine
Threonine
Phenylalanine
Leucine
Corn (maize)
and other grains
Isoleucine
Tryptophan
Lysine
Beans
and other
legumes
Fig. 41-3
Nutrition: Lipids
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Fat, oils, and cholesterol
Saturated fats (solids at room temperature) usually
come from animals
 Exceptions
are palm oil and coconut oil
 Contain mostly saturated fats
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Butter and meats, such as marbled red meats and
bacon, contain saturated fats
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Food High in Trans-fat
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© Benjamin F. Fink, Jr./Brand X/Corbis
12
Nutrition: Vitamins
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Vitamins are organic molecules required in the diet
in small amounts
Must be obtained externally
13 vitamins essential to humans have been identified
Vitamins are grouped into two categories: fatsoluble and water-soluble
Nutrition: Minerals
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Minerals are simple inorganic nutrients, usually
required in small amounts
Nutrition: Fiber
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Includes various undigestible carbohydrates derived
from plants
Food sources rich in fiber include beans, peas, nuts,
fruits, and vegetables
Technically, fiber is not a nutrient for humans
 Cannot
be digested
 Soluble fiber combines with bile acids and cholesterol
in the small intestine and prevents them from being
absorbed
Fiber Rich Food
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© Amiard/Photocuisine/Corbis
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Dietary Deficiencies
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Undernourishment is the result of a diet that
consistently supplies less chemical energy than the
body requires
Malnourishment is the long-term absence from the
diet of one or more essential nutrients
Undernourishment
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An undernourished individual will
 Use
up stored fat and carbohydrates
 Break down its own proteins
 Lose muscle mass
 Suffer protein deficiency of the brain
 Die or suffer irreversible damage
Malnourishment
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Malnourishment can cause deformities, disease, and
death
Malnourishment can be corrected by changes to a
diet
Fig. 41-4
Energy Sources and Stores
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Food energy balances the energy from metabolism,
activity, and storage
Nearly all of an animal’s ATP generation is based on
oxidation of energy-rich molecules: carbohydrates,
proteins, and fats
Animals store excess calories primarily as glycogen
in the liver and muscles
Energy is secondarily stored as adipose, or fat, cells
When fewer calories are taken in than are
expended, fuel is taken from storage and oxidized
Overnourishment and Obesity
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Overnourishment causes obesity, which results from
excessive intake of food energy with the excess
stored as fat
Obesity contributes to diabetes (type 2), cancer of
the colon and breasts, heart attacks, and strokes
Fig. 41-22
100 µm
Obesity and Evolution
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The problem of maintaining weight partly stems from
our evolutionary past, when fat hoarding was a
means of survival
A species of birds called petrels become obese as
chicks; in order to consume enough protein from highfat food, chicks need to consume more calories than
they burn
You should now be able to:
1.
Distinguish between a complete digestive tract and
a gastrovascular cavity
2.
Describe the four main stages of food processing
3.
Describe the functions of nutrients
4.
Distinguish among undernourishment,
overnourishment, and malnourishment
6.
Follow a meal through the mammalian digestive
system:
–
–
7.
8.
List important enzymes and describe their roles
Compare where and how the major types of
macromolecules are digested and absorbed
Relate variations in dentition with different diets
Explain where and in what form energy-rich
molecules may be stored in the human body
In animal diets, essential amino
acids are which of these?
a.
b.
c.
d.
e.
all the amino acids required to make proteins
all the amino acids that cannot be made from organic
nitrogen compounds
all the organic compounds containing amino groups
all the amino acids that can be obtained from plant
foods
all the amino acids that can be obtained from animal
foods
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
Which of the following is an adaptive
advantage of having a complete
digestive tract that is not true for a
gastrovascular cavity with one
opening?
a.
b.
c.
d.
e.
Extracellular digestion can occur.
Teeth and tentacles can help with ingestion.
It allows more surface area for absorption.
It allows organization into specialized compartments.
It allows elimination of undigested wastes.
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
In humans, the first opportunity for
ingested food to be broken down
by hydrolysis is in the
a.
b.
c.
d.
e.
mouth.
Stomach.
Liver.
small intestine.
large intestine.
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
Which of the following is directly
caused by the hydrochloric acid (pH
2) in the stomach cavity?
a.
b.
c.
d.
e.
hydrolysis of polypeptides into amino acid.
hydrolysis of fats into fatty acids and glycerol
activation of pepsinogen into pepsin enzyme
initial development of stomach ulcers
secretion of mucus and constant production of new
epithelial cells
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
What is the role of bile salts in fat
digestion?
a.
b.
c.
d.
e.
hydrolyzing fat molecules in globules to glycerol and
fatty acids
separating individual fat molecules from each other
dissolving fats in water
preventing small fat droplets from coalescing into
larger globules
triggering the activation of lipases from the pancreas
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
If we follow a fatty acid that is absorbed
into an intestinal epithelial cell, we would
find it doing all of the following except
which one?
a.
b.
c.
d.
e.
being synthesized into a triglyceride in the epithelial cell
entering a lacteal vessel as a chylomicron
entering a blood vessel as a chylomicron
being incorporated into chylomicrons in the epithelial cell
exiting the epithelial cell by exocytosis of the
chylomicron
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.
What is the adaptive function of
specialized digestive tract chambers in
vegetarian animals like cows and horses?
a.
b.
c.
d.
e.
to maintain low pH for stomach enzymes
for entry of bile and pancreatic enzymes
for storage of partially digested plant material
for symbiotic bacteria required for cellulose digestion
for consolidation of undigested waste before defecation
Copyright © 2008 Pearson
Education, Inc., publishing as
Pearson Benjamin Cummings.