evolutionary digestive adaptations in vertebrates digestive systems of vertebrates are variations...
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Evolutionary Digestive Adaptations in Vertebrates
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: 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
(c) Omnivore
Molars
(b) Herbivore
(a) Carnivore
Canines Premolars
Fig. 41-19
Cecum
Small intestine
HerbivoreCarnivore
Colon(largeintestine)
StomachSmall intestine
Fig. 41-20
Esophagus
OmasumAbomasum
Intestine
Rumen Reticulum1 2
4 3
Nutritional Aspects in Assimilation
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
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 is the preferred direct energy
source in cells. Plants store glucose as starch Animals store glucose as glycogen
Nutrition: Proteins
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
Beans and otherlegumes
Corn (maize)and other grains
Lysine
Essential amino acids for adults
Tryptophan
Isoleucine
Leucine
Phenylalanine
Threonine
Valine
Methionine
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
Butter and meats, such as marbled red meats and bacon, contain saturated fats
Food High in Trans-fat
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© Benjamin F. Fink, Jr./Brand X/Corbis
Nutrition: Vitamins
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:
fat-soluble and water-soluble
Nutrition: Minerals
Minerals are simple inorganic nutrients, usually required in small amounts
Nutrition: Fiber
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
Dietary Deficiencies
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
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
Malnourishment can cause deformities, disease, and death
Malnourishment can be corrected by changes to a diet
Fig. 41-4
Energy Sources and Stores
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
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 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 high-fat 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:– List important enzymes and describe their
roles– Compare where and how the major types
of macromolecules are digested and absorbed
7. Relate variations in dentition with different diets
8. 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?
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a. all the amino acids required to make proteins
b. all the amino acids that cannot be made from organic nitrogen compounds
c. all the organic compounds containing amino groups
d. all the amino acids that can be obtained from plant foods
e. all the amino acids that can be obtained from animal foods
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?
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a. Extracellular digestion can occur.b. Teeth and tentacles can help with ingestion. c. It allows more surface area for absorption.d. It allows organization into specialized
compartments. e. It allows elimination of undigested wastes.
In humans, the first opportunity for ingested food to be broken down by hydrolysis is in the
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a. mouth.b. Stomach.c. Liver.d. small intestine.e. large intestine.
Which of the following is directly caused by the hydrochloric acid (pH 2) in the stomach cavity?
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a. hydrolysis of polypeptides into amino acid.
b. hydrolysis of fats into fatty acids and glycerol
c. activation of pepsinogen into pepsin enzyme
d. initial development of stomach ulcerse. secretion of mucus and constant
production of new epithelial cells
What is the role of bile salts in fat digestion?
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a. hydrolyzing fat molecules in globules to glycerol and fatty acids
b. separating individual fat molecules from each other
c. dissolving fats in waterd. preventing small fat droplets from
coalescing into larger globulese. triggering the activation of lipases from
the pancreas
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?
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a. being synthesized into a triglyceride in the epithelial cell
b. entering a lacteal vessel as a chylomicronc. entering a blood vessel as a chylomicrond. being incorporated into chylomicrons in the
epithelial celle. exiting the epithelial cell by exocytosis of
the chylomicron
What is the adaptive function of specialized digestive tract chambers in vegetarian animals like cows and horses?
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a. to maintain low pH for stomach enzymesb. for entry of bile and pancreatic enzymesc. for storage of partially digested plant
materiald. for symbiotic bacteria required for cellulose
digestione. for consolidation of undigested waste before
defecation