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Animal Systems:
Feeding and Digestion
Chapter 27.1
Obtaining Food

All animals are heterotrophs

Filter feeders
• Modified gills filter food out of water

Detritivores
• Feed on decaying bits of plant & animals

Carnivores
• Eat other animals

Herbivores – Eat plants
Nutritional Symbionts

Parasites


One organism benefits
while the other is harmed
Mutualism

Both organisms benefit
Processing Food - Digestion
Intracellular Digestion –
Food is digested inside
specialized cells that pass
nutrients to other cells by
diffusion.
 Extracellular Digestion Food is broken down outside
cells in a digestive system
and is then absorbed.

Extracellular Digestion

Gastrovascular Cavities
Present in invertebrates
 Interior body space whose
tissues carry out digestive
functions
 Single opening for
ingestion and excretion
 Cells lining the cavity
absorb nutrients from food

Extracellular Digestion

Digestive Tracts
Most vertebrates but
some invertebrates
 Digestion is through a
tube with two separate
openings
 Food moves in one
direction (Mouth to anus)
 Intestines absorb
nutrients

Specializations for Different Diets

Specialized mouthparts
Carnivores – Incisors, Canines
 Herbivores – Molars and Premolars

Specialized Digestive Tracts

Carnivores


Short intestines with
meat digesting
enzymes
Herbivores

Long intestines with
microbial symbionts
that digest cellulose
Animal Systems:
Respiration
Chapter 27.2
Respiratory System

Function: Provide oxygen
gas needed for cellular
respiration and remove
carbon dioxide from the body

Invertebrate Organs:
 Gills and trachae

Main Vertebrate Organs:

Nose, mouth, pharynx,
larynx, trachea, bronchi,
bronchioles, lungs, gills,
diaphragm
Respiration in animals

Whether they live in water or on land, all
animals must respire.




To respire means to take in oxygen and give
off carbon dioxide.
Some animals rely of simple diffusion
through their skin to respire.
While others…
Have developed large complex organ
systems for respiration.
Respiratory Systems

Respiration involves diffusion

Respiration requires diffusion of O2 and CO2 across cell
membranes
• Diffusion of O2 and CO2 is passive
• Occurs if different concentrations of O2 or CO2 on either side of
membrane
Respiratory Systems

Respiratory organs have
Large surface areas
 Are in contact with air or water
 Moist
 Selectively permeable
 Balance the concentrations of oxygen
and CO2 on either side of the
respiratory membrane (diffusion)

Specialized structures

Structures specialized
for gas exchange
include:
 gills (aquatic animals)
 spiracles (terrestrial
insects)
 lungs (most terrestrial
vertebrates)
Aquatic invertebrates

Aquatic animals have naturally moist
respiratory surfaces, and some animals
simply allow gases to diffuse through
their skins.

Example: jellyfish and anemones
Aquatic invertebrates +
vertebrates

Some larger aquatic invertebrates and chordates
(except reptiles and mammals) exchange O2 and
CO2 through gills.

Gills are organs that have lots of blood vessels that
bring blood close to the surface for gas exchange.
Aquatic Gills
Water flows
through the mouth
then over the gills
where oxygen is
removed
 Carbon dioxide
and water are
then pumped out
through the
operculum

Terrestrial Invertebrates


Terrestrial invertebrates have respiratory surfaces
covered with water or mucus. (Reduces water loss)
There are many different specialized respiratory
organs in terrestrial invertebrates.



Spiders use parallel book lungs
Insects use openings called spiracles where air enters the
body and passes through a network of tracheal tubes for
gas exchange
Snails have a mantel cavity that is lined with moist tissue
and an extensive surface area of blood vessels.
How does respiration in aquatic invertebrates differ from that in
terrestrial invertebrates?
Invertebrate Respiratory Systems
Gill
Tracheal
tubes
Siphons
Movement of water
Insect
Mollusk
Airflow
Spider
Book
lung
Spiracles
Vertebrate respiratory
systems

Chordates have one of two
basic structures for
respiration:

Gills – for aquatic chordates
• Example: Tunicates, fish and
amphibians

Lungs - for terrestrial
chordates
• Examples: Adult amphibians,
reptiles, birds, and mammals
Vertebrate lungs

As you move from amphibians to mammals
the surface area of the lungs increases


Insures a greater amount of gas exchange (or a
two way flow of air).
Birds, by contrast have lungs and air sacs
which have only a one-way flow of air.


This allows for them to have constant contact
with fresh air.
This adaptation enables them to fly at high
altitudes where there is less oxygen.
Vertebrate Lungs
Nostrils, mouth, and throat
Trachea
Lung
Air sac
Salamander
Lizard
Primate
Pigeon
Human respiratory system

Parts of the respiratory
system include:
Trachea
 Bronchi
 Bronchioles
 Alveoli

The Human Respiratory
System
Respiration and the
respiratory System

Alveoli

Air sacs in the lungs that allow the exchange of oxygen and carbon
dioxide so oxygen can enter the blood stream.
Circulation and Gas
Exchange
Recall the
interconnection
between circulation and
the respiratory system.
 Gas exchange at the
lungs and in the body
cells moves oxygen into
cells and carbon dioxide
out.

Movement of Oxygen and Carbon
Dioxide In and Out of the Respiratory
System
Oxygen-rich
air from environment
Bronchi
Trachea
BIG
QUESTION
…
Nasal
cavities
Pharynx
Trachea
Bronchi
Bronchioles
Oxygen and
carbon dioxide
exchange at
alveoli
Alveoli
Bronchioles
Pharynx
Nasal
cavities
WHY DO ANIMALS BREATHE?
Carbon
dioxide-rich
air to the
environment
Gills exchange gases in fish. What is the
site of gas exchange in mammals?
25%
1.
2.
3.
4.
25%
25%
25%
Alveoli
Tracheids
Bronchi
Esophagus
1
2
3
4
Animal Systems:
Circulation
Chapter 27.3
Functions of the circulatory system

Transports materials








Nutrients from digested food
Respiratory gases: CO2 and O2
Waste materials: Toxins and nitrogenous wastes
Antibodies
Hormones
Enzymes
Immune functions
Maintains homeostasis


Blood pH
Heat transport
Animal Circulatory Systems

Types of circulatory systems:
gastrovascular, open, closed.

Vascular system: arteries, veins,
capillaries.

Capillary - tissue fluid exchange.
Larger Animals Without a Separate Circulatory
System
Cnidarian Gastrovascular Systems
Some larger animals such as
hydras, sea anemones,
jellyfish, and flatworms
lack a true circulatory
system.
The gastrovascular cavity
extends to most areas of the
body in these animals and
serves as a circulatory
system as well as a
digestive cavity.
Circulation in Simple Invertebrates
Gastrovascular cavity
 No system is required
 Single opening:
exchange of materials
with the environment
 Central cavity for
digestion and
distribution of
substances throughout
the body
 Body walls are two cell
layers thick 
materials undergo
diffusion
 Cnidarians (e.g. Hydra)
and flatworms (e.g.
planarians)
Flatworm and Hydra Gastrovascular
System
Circulatory Systems

For larger or more active animals, some
form of more efficient circulatory
systems are necessary for internal
transport.

Two types of circulatory system are found:
• Open Circulatory Systems
• Closed Circulatory Systems
Open Circulatory System
Phylum Arthropoda,
Phylum Mollusca (with one
exception)
 Heart(s) pumps blood 
empties into spongy
cavities (sinuses) 
contacts tissues to supply
with oxygen  blood then
travels back to heart(s)
(without blood vessels)
 Blood - Hemolymph

Open Circulatory System
Open Circulatory System

Advantage - Exchange of materials is
direct between the hemolymph and
tissues. There is no diffusion barrier.

Disadvantage - Little fine control over
distribution of the hemolymph to body
regions. No mechanism for reducing
flow to a specific part of an organ.
Open Circulatory System

Open circulatory systems
tend to be found in more
inactive animals.

Most molluscs have an
open system, but the
highly active cephalopods
(squid and octopus) have
evolved a closed system.
Closed Circulatory System

The blood is contained
within a completely closed
system of vessels.

Vessels form a closed loop,
usually with some sort of
pumping organ like a heart
or contractile vessels.

Vessels branch into smaller
and smaller tubes that
penetrate among the cells
of tissues.
Closed Circulatory System
Advantages:

Fine-scale control over the distribution of
blood to different body regions is possible.

Muscular walls of vessels can constrict and
dilate to vary the amount of flow through
specific vessels.

Blood pressures are fairly high and the
circulation can be vigorous.
Closed Circulatory System:
Single Loop Circulation





Blood circulates through the
body in one direction
Heart contains 1 ventricle & atrium
Ventricle pumps blood out of heart
to gills
Gills exchange CO2 w/ O2 and
bring oxygenated blood to body
tissues and then back to heart
Atrium receives deoxygenated
blood from tissues
(and capillaries)
Closed Circulatory System:
Double Loop Circulation
As vertebrates evolved one pump
was not enough to deliver blood to
organs.
 Double Loop Circulation:
 Lungs for respiration
 Double loop
 Two pump circulatory system

Closed Circulatory System:
Double Loop Circulation




Oxygen poor blood is pumped from
right side of the heart to the lungs.
The lungs undergo gas exchange so
the oxygen rich blood can be
transported back to the left side of the
heart.
The oxygenated blood transports to
body tissues, which undergo gas
exchange.
Deoxygenated blood (CO2) is
transported back to the right side of
the heart and the process starts over.
Circulatory Systems
•
•
•
•
•
The cardiovascular system consists of the
heart and the 3 types of blood vessels that
carry blood throughout your body.
The blood vessels—arteries, capillaries, and
veins—carry blood pumped by the heart.
Arteries are blood vessels that carry blood
away from the heart and to the body’s organs.
Capillaries are tiny blood vessels that allow the
gas exchange between body cells and blood.
Veins carry blood back to heart
Evolution of Circulatory Systems
Evolution of Circulatory Systems
Mammalian Circulatory
System

Mammalian hearts have 2
sides separated by a
partition
Right: Oxygen poor blood
 Left: Oxygen rich blood
 Each side has an upper
chamber (atrium) and a
lower chamber (ventricle)

• This is called a 4 chamber
heart
Cardiac cycle
Evolution of Circulatory
Systems in Vertebrates
Animal Systems:
Excretion
Chapter 27.4
Essential Questions
 How
do animals manage toxic
nitrogenous waste?
 How do aquatic animals
eliminate wastes?
 How do land animals remove
wastes while conserving water?
Excretion


Nitrogenous wastes are produced as a result of
cellular respiration (exchanging O2 + CO2)
Nitrogenous wastes can be secreted as:



Ammonia – water soluble and toxic
• Usually released by aquatic organisms
Urea – ammonia combined with CO2 in the liver
• Less toxic and conserves water
• Most vertebrates
• Released diluted as urine
Uric acid – excreted as a paste or crystals
• Produced by birds and reptiles
Excretion
The excretory system collects wastes and
delivers them to organs that will be released
from the body.
 Small animals in wet environments get rid of
ammonia by allowing it to diffuse out of their
body fluids across their skin.
 Most larger animals have excretory systems
that process ammonia and eliminate it from
the body.

Excretion
Most complex excretory organs
are the kidneys in vertebrates
 Other structures for excretion
 Nephredia/Excretory pores

• Flat worms, Annelids
 Malpighian
• Arthropods

tubules
All involve a type of tubular
system
Maintaining Water Balance

Excretory systems are extremely important in
maintaining the proper balance of water in
blood and body tissues

May also excrete excess water or have to
conserve water.
Kidneys
 Separate
wastes and excess water
from blood to form urine
 Usually cannot excrete excess salt.
Freshwater Animals
 Freshwater
invertebrates lose
ammonia to their environment by
simple diffusion across their skin.
 Freshwater fishes and amphibians
eliminate ammonia by diffusion
across the same gill membranes they
use for respiration.
Saltwater Animals
 Typically
release ammonia by
diffusion across their body
surfaces or gill membranes.
 Many marine invertebrates have
body fluids with water
concentrations similar to that of
the seawater around them.
Excretion in Terrestrial Animals
 Land
animals can lose large amounts of
water from respiratory membranes that
must be kept moist.
 And must eliminate nitrogenous wastes
in ways that require disposing of water.
 Therefore, terrestrial animals have to
have adaptations to conserve water
loss.
Terrestrial Invertebrates

Some produce urine in nephridia


Annelids, Mollusks
Nephridia
Tubelike excretory structures that filter body
fluid.
 Leaves the body through excretory pores.

Terrestrial Invertebrates
Insects and arachnids
convert ammonia into uric
acid
 Malpighian tubules
 Absorb uric acid from body
fluids
 Concentrate the wastes
and add them to digestive
wastes.

Terrestrial Invertebrates
Water is absorbed from
wastes
 Crystals form a thick
paste which leaves the
body through the anus
 Paste contains little water


Minimizes water loss
Terrestrial Vertebrates
Mammals and land
amphibians convert
ammonia into urea
 Excreted in urine by the
kidneys.
 Reptiles and birds convert
ammonia into uric acid,
which leaves the body as a
thick white milky paste (bird
droppings)

Terrestrial Vertebrates
 Most
vertebrate kidneys cannot
excrete concentrated salt
 Most vertebrates cannot survive
by drinking seawater
 All that extra salt would
overwhelm the kidneys, and the
animal would die of dehydration.