Chapter 41

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 41Chapter 41

Animal Nutrition


Overview: The Need to Feed

• Every meal reminds us that we are heterotrophs, dependent on a regular supply of food

• In general, animals fall into three categories:

– Herbivores eat mainly autotrophs (plants and algae)

– Carnivores eat other animals

– Omnivores regularly consume animals as well as plants or algal matter


• An adequate diet must satisfy three needs:

– Fuel for all cellular work

– Organic raw materials for biosynthesis

– Essential nutrients, substances that the animal cannot make for itself

• Main feeding mechanisms: suspension feeding, substrate feeding, fluid feeding, bulk feeding


LE 41-2a

Baleen

LE 41-2b

Caterpillar Feces


Glucose Regulation as an Example of Homeostasis

• Animals store excess calories as glycogen in the liver and muscles and as fat

• Glucose is a major fuel for cells

• Hormones regulate glucose metabolism

• When fewer calories are taken in than are expended, fuel is taken from storage and oxidized

LE 41-3

STIMULUS:Blood glucose

level risesafter eating.

STIMULUS:Blood glucose

level dropsbelow set point.

Homeostasis:90 mg glucose/100 mL blood

LE 41-4

100 µm


Obesity as a Human Health Problem

• The World Health Organization now recognizes obesity as a major global health problem

• Obesity contributes to a number of health problems, including diabetes, cardiovascular disease, and colon and breast cancer


LE 41-5

LeptinPYY

Insulin

Ghrelin


• The complexity of weight control in humans is evident from studies of the hormone leptin

• Mice that inherit a defect in the gene for leptin become very obese


Obesity and Evolution

• The problem of maintaining weight partly stems from our evolutionary past, when fat hoarding was a means of survival


Concept 41.2: An animal’s diet must supply carbon skeletons and essential nutrients

• An animal must obtain carbon skeletons from its food to build complex molecules

• A malnourished animal is missing one or more essential nutrients in its diet


Essential Amino Acids

• Animals require 20 amino acids and can synthesize about half from molecules in their diet

• Essential amino acids, must be obtained from food in preassembled form

• Malnutrition called protein deficiency occurs when a diet doesn’t contain all needed amino acids


Kwashiorkor

Caused by a protein deficiency

LE 41-10

Methionine

Valine

Threonine

Phenylalanine

Leucine

Isoleucine

Tryptophan

Lysine

Essential amino acids for adults

Beansand otherlegumes

Corn (maize)and other grains



Vitamins

• Vitamins are organic molecules required in the diet in small amounts

• 13 vitamins essential to humans have been identified

• Vitamins are grouped into two categories: fat-soluble and water-soluble




Minerals

• Minerals are simple inorganic nutrients, usually required in small amounts



Concept 41.3: The main stages of food processing are ingestion, digestion, absorption, and elimination

• Ingestion

• Digestion

• Absorption

• Elimination

LE 41-12

Pieces of food

Chemical digestion(enzymatic hydrolysis)

Food

Nutrientmoleculesenter bodycells

Smallmolecules

Undigestedmaterial

ELIMINATIONABSORPTIONDIGESTIONINGESTION

Mechanicaldigestion


• Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients

Video: Hydra Eating Daphnia

Gastrovascularcavity

Mouth

Food

Tentacles

Epidermis

GastrodermisMesoglea

Gland cells

Flagella

Nutritivemuscularcells

Food vacuoles

Mesoglea

LE 41-14a

GizzardIntestine

Anus

CropEsophagus

Pharynx

Mouth

Earthworm

Typhlosole

Lumen of intestine

LE 41-14b

Foregut Midgut Hindgut

Rectum

Anus

Esophagus

MouthCrop

Gastric cecaGrasshopper

LE 41-14c

Anus

Esophagus

Mouth

Crop

Bird

StomachGizzard

Intestine


Concept 41.4: Each organ of the mammalian digestive system has specialized food-processing functions

• The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts

• Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder

• Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal

LE 41-15a

Esophagus

Pharynx

Oral cavity

Stomach

Pyloricsphincter

Cardiacorifice

Liver

Tongue

Parotid glandSublingual gland

Submandibular gland

Salivaryglands

Ascendingportion oflarge intestine

Gall-bladder

Pancreas

Ileumof small intestine

Rectum

Anus

Appendix

Cecum

Largeintestine

Smallintestine

Duodenum ofsmall intestine

Esophagus

Stomach

Liver

Salivaryglands

Gall-bladder

Pancreas

Rectum

Anus

Largeintestines

Smallintestines

Mouth

A schematic diagram of thehuman digestive system


The Oral Cavity, Pharynx, and Esophagus

• In the oral cavity, food is lubricated and digestion begins

• Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers

LE 41-16_3

Epiglottisup

Bolus of food

Esophagealsphinctercontracted

Esophagus

To stomachTo lungs

Trachea

Tongue

Pharynx

Glottis

Larynx

Esophagealsphincterrelaxed

Epiglottisdown

Glottis upand closed

Epiglottisup

Esophagealsphinctercontracted

Relaxedmuscles

Glottis downand open

Relaxedmuscles

Contractedmuscles

Stomach


The Stomach

• The stomach stores food and secretes gastric juice, which converts a meal to acid chyme

• Gastric juice is made up of hydrochloric acid and the enzyme pepsin

• Pepsin is secreted as inactive pepsinogen; pepsin is activated when mixed with hydrochloric acid in the stomach

• Mucus protects the stomach lining from gastric juice


Pepsinogen Pepsin

HCl

LE 41-17

Esophagus

Cardiac orifice

Pyloric sphincter

Smallintestine Folds of

epithelialtissue

Stomach

Epithelium

Pepsin(active enzyme)

Pepsinogen

HCl

Pepsinogen and HClare secreted into the lumen of the stomach.

HCl convertspepsinogen to pepsin.

Pepsin then activatesmore pepsinogen,starting a chainreaction. Pepsinbegins the chemicaldigestion of proteins.

Parietal cellChief cell

Chief cells

Mucus cells

Parietal cells

Interior surface of stomach

Gastric gland

5 µ

m


• Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Helicobacter pylori

Bacteria

Mucuslayer ofstomach

1 µ

m


The Small Intestine

• The small intestine is the longest section of the alimentary canal

• It is the major organ of digestion and absorption

LE 41-19

Stomach

Pancreas

Liver

Gall-bladder

Duodenum ofsmall intestine

Intestinaljuice

Bile

Acid chyme

Pancreatic juice


• The pancreas produces proteases, protein-digesting enzymes that are activated after entering the duodenum

LE 41-20

Pancreas

Lumen of duodenum

Membrane-boundenteropeptidase

Inactivetrypsinogen

Other inactiveproteases Active

proteases

Trypsin


• The liver produces bile, which aids in digestion and absorption of fats

• The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes

LE 41-21

Oral cavity,pharynx,esophagus

Stomach

Lumen ofsmall intes-tine

Smaller polysac-charides, maltose

Polysaccharides Disaccharides

Carbohydrate digestion

Salivary amylase

Polysaccharides

Pancreatic amylases

Maltose and otherdisaccharides

Epitheliumof smallintestine(brushborder)

Disaccharidases

Monosaccharides

Protein digestion Nucleic acid digestion

Proteins

Fat digestion

Fat globulesDNA, RNA

Fat dropletsNucleotides

Bile salts

Pancreatic lipase

Pancreaticnucleases

Nucleotidases

Glycerol, fattyacids, glycerides

Nitrogenous bases,sugars, phosphates

Nucleosides

Nucleosidasesand phosphatases

Dipeptidases, carboxy-peptidase, and aminopeptidase

Amino acids

Amino acids

Small peptides

Pancreatic carboxypeptidase

Pancreatic trypsinand chymotrypsin

Smaller polypeptides

Polypeptides

Small polypeptides

Pepsin

LE 41-22

Pancreas

Stomach

Entero-gastrone

Gall-bladder

Liver

Duodenum

Secretin

CCK

CCK

Stimulation

Inhibition

Gastrin

Key


Absorption of Nutrients

• The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen

• The enormous microvillar surface greatly increases the rate of nutrient absorption

LE 41-23

Key

Nutrientabsorption

Microvilli(brush border)

Epithelial cells

Lacteal

Lymphvessel

Villi

Largecircularfolds

Epithelialcells

Bloodcapillaries

Vein carrying bloodto hepatic portalvessel

Muscle layers

Villi

Intestinal wall


• Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream

• After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells

Fat dropletscoated withbile salts

Fat globule

Bile salts

Micelles madeup of fatty acids,monoglycerides,and bile salts

Epitheliumof smallintestine

Epitheliumof lacteal

Lacteal


The Large Intestine

• The large intestine, or colon, is connected to the small intestine

• Its major function is to recover water that has entered the alimentary canal


• The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins


Concept 41.5: Evolutionary adaptations of vertebrate digestive systems are often associated with diet

• Digestive systems of vertebrates are variations on a common plan

• However, there are intriguing adaptations, often related to diet


Some Dental Adaptations

• Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet

• Mammals have specialized dentition that best enables them to ingest their usual diet

LE 41-26

Incisors

Carnivore

CaninesPremolars

Molars

Herbivore

Omnivore


Stomach and Intestinal Adaptations

• Herbivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation

LE 41-27

Smallintestine

Stomach

Cecum

Colon(largeintestine)

Carnivore Herbivore

Small intestine


Symbiotic 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

LE 41-28

Intestine Rumen

Reticulum

Omasum

EsophagusAbomasum

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Chapter 41

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