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Path Of Food Through The Animal Body
Chapter 24
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Outline
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Food Energy
Digestive Systems
 Types
 Organs
- Accessory
Homeostasis
Osmoregulation
Vertebrate Kidney
 Nephrons
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Calories For Energy
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Food provides animals both a source of
energy and a supply of raw materials.
 Fats have more energy-rich carbonhydrogen bonds and thus a higher energy
content than carbohydrates or proteins.
 Carbohydrates are obtained primarily from
cereals, grains, fruits and vegetables, and
contain on average 4.1 calories per gram.
- Used for energy.
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Calories For Energy
Dietary Fats are obtained from oil
margarine, and butter, and contain 9.3
calories per gram.
- Used to construct cell membrane and
other cellular structures.
 Protein can be obtained from dairy
products, poultry, fish, and meats and have
4.1 calories per gram.
- Used as building materials for cell
structures, enzymes, hemoglobin.

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Nutrition Pyramid
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Essential Substances for Growth
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Many vertebrates are unable to manufacture
one or more of 20 essential amino acids
(necessary for metabolism), and thus must
obtain them from food.
 Vitamins are organic substances used in
trace amounts.
 Trace Elements are minerals required in
very small amounts.
- Iodine, cobalt, zinc, molybdenum,
manganese, and selenium.
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Types of Digestive Systems
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Heterotrophs are divided into three main
groups:
 Herbivores - eat exclusively plants.
 Carnivores - eat exclusively meat.
 Omnivores - eat both plants and meat.
Single-celled organisms digest food
intracellularly.
Other animals digest food extracellularly
within digestive cavity.
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Types of Digestive Systems
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Specialization occurs when the digestive
tract (alimentary canal) has a separate
mouth and anus, so that food transport is
one way.
 Ingested food may be stored in specialized
region of tract, or may first be subjected to
physical fragmentation, followed by
chemical digestion.
 Products then pass through epithelial lining
of the gut into blood (absorption).
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One-Way Digestive Tracts
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Vertebrate Digestive Systems
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Vertebrate system consists of tubular
gastrointestinal tract and accessory digestive
organs.
 Mouth and Pharynx
 Esophagus - Delivers food to stomach.
 Stomach - Preliminary digestion.
 Small Intestine - Digestion and absorption.
 Large Intestine - Water/ mineral absorption.
 Cloaca / Rectum - Waste expulsion.
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Human Digestive System
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Vertebrate Digestive Systems
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In general, carnivores have relatively shorter
intestines than herbivores.
 Plant cellulose resists digestion.
- Ruminants (cows) contain fourchambered stomachs.
- Other herbivores (rabbits - horses)
posses cecum at beginning of large
intestine.
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Vertebrate Digestive Systems
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Layered structure of gastrointestinal tract.
 Mucosa
 Submucosa
 Muscularis
 Serosa
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Mouth and Teeth
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Carnivorous mammals have pointed teeth,
lacking flat grinding surfaces, adapted to
cutting and shearing.
Herbivorous mammals have large and flat
teeth adapted to grinding cellulose.
Human Mouths are basically carnivorous in
the front, and herbivorous in the back.
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Mouth and Teeth
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Tongue mixes food with saliva to moisten
and lubricate food.
 Contains amylase which initiates
breakdown of starch into maltose.
- Presence of food in the mouth triggers
increased rate of secretion, as tastesensitive neurons send impulses to the
brain which responds by stimulating
salivary glands.
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Mouth and Teeth
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Tongue moves food to the back of the mouth
prior to swallowing .
Soft palate elevates and pushes against
back wall of pharynx.
 Stimulates neurons and sends impulses to
swallowing center in the brain.
 Muscles contract and raise the larynx.
- Pushes glottis against epiglottis to keep
food out of respiratory tract.
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Human Pharynx, Palate, and Larynx
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Esophagus and Stomach
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Swallowing center stimulates successive
waves of contraction (peristalsis) that moves
food along esophagus to stomach.
 Movement of food from esophagus into
stomach controlled by either smooth
muscle (sphincter) or true sphincter.
Stomach is a saclike portion of digestive tract
with convoluted surface enabling expansion.
 Allows for sporadic gorging.
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Esophagus and Stomach
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Stomach contains extra layer of smooth
muscle for mixing food with gastric juices.
 Parietal cells secrete hydrochloric acid.
 Chief cells secrete pepsinogen.
Human stomach produces about 2 liters of
HCl and other gastric secretions daily.
 Acidic solution kills most bacteria.
- Chyme - mixture of food and gastric
juices.
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Esophagus and Stomach
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Hormone gastrin regulates HCl synthesis.
 Overproduction of gastric acid can
potentially eat through stomach wall.
- Gastric ulcers
 Susceptibility is increased when
mucosal barriers are weakened by
Heliobacter pylori infection.
Chyme leaves stomach through pyloric
sphincter and enters small intestine.
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Stomach and Gastric Glands
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Small Intestine
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Small intestine breaks down large molecules
into small molecules that absorb into
bloodstream.
 Pancreas secretes enzymes into
duodenum.
 Liver secretes bile salts into duodenum to
make fats water soluble.
Rest of small intestine (ilium) is devoted to
absorption, and is covered with villi to
increase absorptive surface.
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Small Intestine
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Large Intestine
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Large Intestine (colon) finishes absorption.
 Primary function is refuse dump.
- Feces (Undigested food and bacteria)
 Rectum
 Anus
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Variations In Vertebrate Digestive Systems
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Most animals lack enzymes necessary to
digest cellulose.
 Four-chambered stomachs
- Rumen
- Reticulum
 Omasum
 Abomasum
 Coprophagy - Eating feces to absorb
nutrients.
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Ruminant Stomach
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Accessory Digestive Organs
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Pancreas
 Contributes secretions to digest protein.
 Produces hormones in islets of Langerhans.
- Controls glucose
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Accessory Digestive Organs
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Liver
 Largest organ in body.
 Delivers bile to duodenum.
 Modifies substances absorbed in
gastrointestinal tract.
- Removes toxins.
 Produces proteins found in blood plasma.
Gallbladder
 Stores bile
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Homeostasis
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Dynamic constancy of internal environment.
 Fluctuate continuously within narrow limits.
Hypothalmus coordinates body temperature
regulation.
 Sweating, Blood Vessel Dissipation
 Shivering, Blood Vessel Constriction
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Homeostasis
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Islets of Langerhans secrete insulin when
glucose levels rise.
Liver secretes glucose when blood glucose
levels fall.
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Homeostasis
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Catabolization produces nitrogenous wastes
that must be eliminated.
 Ammonia
 Urea
 Uric Acid
- Uricase
 Allantonin
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Osmoregulatory Organs
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Osmoregulation is process of regulating
body’s osmotic composition.
 Filter fluid into tubules and reabsorb ions
and water.
- Flatworms - Protonephridia
- Earthworms - Nephridia
- Insects - Malpighian Tubules
- Vertebrates - Kidneys
 Selective absorption
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Evolution of Vertebrate Kidney
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Kidney is complex organ made up of
repeating disposal units (nephrons).
 Blood pressure forces fluid in blood past
filter (glomerulus).
- Retains large molecules but allows water
and small molecules to pass through.
 Urine
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Evolution of Vertebrate Kidney
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Freshwater Fish
 Faced two problems:
- Water tends to enter body from
environment.
 Do not drink water and excrete large
volume of dilute urine.
- Solutes tend to leave body and enter
environment.
 Reabsorb ions across nephron
tubules.
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Vertebrate Nephron
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Evolution of Vertebrate Kidney
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Marine Bony Fish
 Body fluids are hypotonic to seawater.
- Water leaves by osmosis across gills.
 Drink large amounts of seawater.
- Most monovalent ions actively
transported out of blood across gills.
- Divalent ions entering blood are
secreted into nephron tubules and
excreted in the urine.
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Evolution of Vertebrate Kidney
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Cartilaginous Fish
 Reabsorb urea from nephron tubules and
maintain blood urea concentration 100
times higher than that of mammals.
- No net movement of water.
Amphibians
 Produce very dilute urine and compensate
for loss of sodium by actively transporting
sodium across skin from surrounding
water.
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Evolution of Vertebrate Kidney
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Reptiles
 Reabsorb salt and water in nephron
tubules, and additional water in cloaca.
Mammals and Birds
 Only vertebrates able to produce urine with
higher osmotic concentration than body
fluids.
- Excrete wastes in small volume of water.
 Loop of Henle portion of nephron
 Cloaca in birds
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Mammalian Kidney
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Each kidney receives blood from renal artery
and produces urine.
 Urine drains from each kidney through
ureter which carries urine to urinary
bladder.
- Renal pelvis divided into:
 Renal cortex
 Renal medulla
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Mammalian Urinary System
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Mammalian Kidney
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Nephron Regions
 Filter
- Bowman’s Capsule
 Glomerulus
 Tube
- Loop of Henle
 Duct
- Collecting Duct
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Mammalian Urinary System
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Kidney At Work
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Five Steps of Urine Formation
 Pressure Filtration
 Reabsorption of Water
 Selective Reabsorption
 Tubular Excretion
 Further Reabsorption of Water
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Review
•
•
•
•
•
Food Energy
Digestive Systems
 Types
 Organs
- Accessory
Homeostasis
Osmoregulation
Vertebrate Kidney
 Nephrons
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies