Chapter 26
Circulation and Gas Exchange
Transport Systems in Invertebrates
• Protozoa
• Surface-to-volume ratios, need gas , nutrient, and waste exchange via simple
diffusion.
• Plasma membrane and cytoplasm are the media where material diffuse
between the organism and environment.
• Sponges
• Circulate water from the external
environment through their bodies,
instead of circulating an internal
fluid.
• Cnidarians (Hydra)
• Fluid filled internal gastrovascular
cavity
• Supplies nutrients for all body cells
lining the cavity, provides oxygen,
reservoir for carbon dioxide and
other wastes.
• Flatworms (Planaria)
• Branches penetrate to all parts of
the body
• Diffusion distances for nutrients,
gases, and wastes are short.
• Disadvantage: limits the animals to
relatively small sizes or to shapes
that maintain small diffusion
distances.
• Pseudocoelom animals
• Coelomic fluid of their body cavity
is used for transport
• Small, movements of the body
against coelomic fluids are in
direct contact with internal tissues
produce adequate transport
• Coelomic animals
• Depend largely on the body cavity
as coelomic transport chamber
• Mollusks
• Separate
circulatory
or
cardiovascular system
• Unidirectional blood vessels.
• Two types of circulatory system
• Open
• Heart pumps hemolymph out into the
body cavity or at least through parts
of the cavity, where hemolymph
bathes the cells, tissues, and organs
• Closed
• Blood circulates in the confines of
tubular vessels. Coelomic fluid of
some invertebrates also has a
circulatory role either in concert with.
Or instead the hemolymph or blood.
• Coelomic fluids
• Supplementary or sole circulatory
system
• May be identical in composition to
interstitial fluids
• Transport gases, nutrients, and
waste products
• Part of hydrostatic skeleton
• Hemolymph
• Circulating fluid of animals with an
open circulatory system
• Arthropods and ascidians
• Heart pumps at low pressures
through vessels to tissues spaces
(hemocoel) and sinuses
• Hemolymph volume is high and
the circulation slow.
• Hemocytes
• Blood cells
• E.g. hemoglobin (respiratory
pigments) – RBC – for oxygen
transport
• Blood clotting
Transport Systems in Vertebrates
• Plasma
• 90% water
• Provides the solvent for dissolving
and transporting nutrients.
• Albumin, fibrinogen, and globulins
– proteins, 7%
• Serum – plasma from which
proteins involved in blood clotting
have been removed.
• 3% - electrolytes, amino acids,
glucose and other nutrients,
enzymes, hormones, metabolic
wastes, etc.
• Formed Elements:
• Red blood cells
• Erythrocytes
• Vary in size, shape and number in
different vertebrates
• Most are nucleated, others are
enucleated
• Hemoglobin – iron containing protein
• Pick up oxygen from environment to
form oxyhemoglobin
• Carbon dioxide carbaminohemoglobin
• White blood cells (leukocytes)
• Scavengers
that
destroy
microorganisms at infection sites,
remove foreign chemicals and
remove debris resulted from injured
cells
• Granulocytes
• Eosinophils – phagocytic and ingests
foreign proteins and immune complex,
allergic reactions
• Basophils – granules release histamine
and heparin
• Neutrophils – chemically attracted to
sites of inflammation and active
phagocytes
• Agranulocytes
• Lymphocytes
• B cells
• T cells
• Monocytes
• Platelets (Thrombocytes)
• Initiate blood clotting
• Blood coagulation
• Blood Vessels
• Arteries
• Elastic, carries blood away from the
heart to the organs and tissues of the
body
• Thicker
• Veins
• Inelastic, large vessels, carry blood
from body tissues toward the heart
• One or more valve is present, thinner
• Arterioles
• Capillaries
• Venules
Hearts and Circulatory Systems of Bony fishes,
Amphibians, and Reptiles
• Bony Fishes
• Two pumping chambers – atrium
and ventricle
• Ventricle pumps blood leaves
the heart via ventral aorta 
gills oxygenated, loses CO2 
enters dorsal aorta  distributes
to all body organs  blood return
to the heart via venous system
• Single circulation circuit
• Amphibians and reptiles
• Evolution of double circulation –
blood passes the heart twice during
its circuit through the body overcome the slow blood-flow
• Heart not fully divided
• Amphibians• Single ventricle pumps blood to the
lungs and to the body – cutaneous
respiration – blood returning from
the skin contributes oxygenated
blood
to
the
ventricle
(pulmocutaneous circuit)
• Reptiles
• Ventricle is partially divided into
right and left side
• Oxygenated blood from the lungs
 return to left side via
pulmonary vein (does not mix)
ventricles contract  pumped
out two aortae for distribution to
the body and lungs
Hearts and Circulatory Systems of Birds,
Crocodilians, and Mammals
• Two types of Circuits
• Pulmonary circulation – supplies
blood only to the lungs, carries
unoxygenated blood from the
heart to the lungs
• Systemic circulation – supplies all
cells, carries oxygenated blood
and return deoxygenated blood to
the heart.
• Mammalian Heart
• Small animal have higher heart
rate
• Due to higher metabolic rate with
decrease body size
• Myocardium - muscle
• Epicardium – outer
• Endocardium – inside
• Atrium and ventricles
• Valves (AV valves and semilunar)
• Heartbeat – sequence of muscle
contractions and relaxations –
cardiac cycle
• Sinoatrial Node (SAA Node) –
pacemaker – initiate the
heartbeat
• SA Node  AV Node  Bundle
of His  left and right branches
 Purkinje fibers
• Systole and Diastole
The Lymphatic System An Open, One-way
System
• Major functions:
• To collect and drain most of the
fluid that seeps from the
bloodstream and accumulates in
the extracellular fluid
• To return small amounts of
proteins that have left the cells
• To transport lipids that have been
absorbed from the small intestine
• To transport foreign particles and
cellular debris to disposal centers
called lymph nodes.
Gas Exchange
• Respiratory surfaces
• Simple diffusion across plasma
membranes
• Tracheae
• Cutaneous (integument or body
surface)
• Gills
• Lungs
Invertebrate Respiratory Systems
• Protozoa
• Diffusion of gases
• Earthworms
• Moist
environments,
uses
integumentary exchange
• Capillary network under the
integument, exchange gases with
the air spaces among soil particles
• Aquatic invertebrates
• Gills
• Terrestrial invertebrates
(centipedes, insects, etc.)
• Tracheal systems – highly branched
chitin-lined tubes
• Open to the outside through spiracles
• Arachnids
• Book lungs – paired of invaginations
of the ventral body wall that are
folded into series of leaflike lamellae
• Molluscan Pulmonata – land
snails and slugs
• Pulmonate lung – opens to the
outside via a pore called
pneumostome
• Derived from a feature in molluscs
in general- the mantle cavity
which houses the gills and other
organs
Vertebrate Respiratory Systems
• Bimodal breathing – ability of an organism to exchange respiratory
gases simultaneously with both air and water.
• Some salamanders, crabs, barnacles, fishes uses gills for water
breathing
• Trimodal – skin, gills, and lungs - cutaneous
• Cutaneous respiration
• Integumentary exchange
• Most highly developed in frogs,
toads, lungless salamanders and
newts.
• Capillary network lies in a plane
directly beneath the epidermis.
• Slimy mucous layer that keep
amphibian skin moist and protect
against injury
• Gills
• Thin, moist and vascularized layer
of epidermis to permit gas
exchange
across
thin
gill
membranes or thin layer of
epidermis over highly vascularized
dermis.
• Larval fishes and amphibians –
external gills
• Adult fishes – internal gills
• Lungs
• Internal sac-shaped respiratory
organ
• Terrestrial vertebrate comprises
one or more internal blind
pouches which air is either drawn
or forced.
• Epithelium
is
thin,
well
vascularized, and divided into
large number of small units which
greatly increase the surface area
for gas exchange between lung
and blood.
• Swim bladder
• Air sac located dorsal to the
digestive tract in the body of many
modern fishes
• Supplementary gas-exchange
organ when fishes could not
obtain enough oxygen through
their gills
• Lung Ventilation
• Physiological principles
• Air moves by bulk flow into and
out of the lungs in the process
called ventilation.
• Carbon dioxide diffuses across the
respiratory surface of the lung
tissue from the pulmonary
capillaries and oxygen diffuses
from the alveoli into the
pulmonary capillaries.
• At systemic capillaries, oxygen
and carbon dioxide diffuse
between
the
blood
and
interstitial fluid in response to
concentration gradients.
• Oxygen and carbon dioxide
diffuse between the intersttial
fluid and body cells.
• Vertebrate exhibit two different mechanisms for lung ventilation on
these principles.
• Amphibians and some retiles use positive pressure pumping
mechanism - pushing air into the lungs
• Most reptiles all birds and mammals use negative pressure system –
they inhale (breathe in) by suction