Evolutionary Digestive Adaptations in Vertebrates Digestive systems of vertebrates are variations on a common plan However, there are intriguing adaptations,

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

22

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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?

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

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?


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


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?


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?


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?


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?


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

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Evolutionary Digestive Adaptations in Vertebrates Digestive systems of vertebrates are variations on a common plan However, there are intriguing adaptations,