Chapter 42
Circulation and Gas Exchange
Overview: Trading with the Environment
• Every organism must exchange materials with its environment
• Exchanges ultimately occur at the cellular level
• In unicellular organisms, these exchanges occur directly with the environment
• For most cells making up multicellular organisms, direct exchange with the environment is not possible
• A salmon’s feathery gills are an example of a specialized exchange system in animals
Concept 42.1: Circulatory systems reflect phylogeny• Transport systems connect the
organs of exchange with the body cells• Most complex animals have internal
transport systems that circulate fluid
Invertebrate Circulation
• The wide range of invertebrate body size and form is paralleled by diversity in circulatory systems
Gastrovascular Cavities
• Simple animals, such as cnidarians, have a body wall only two cells thick that encloses a gastrovascular cavity
• This cavity functions in both digestion and distribution of substances throughout the body
• Some cnidarians, such as jellyfish, have elaborate gastrovascular cavities
LE 42-2
Mouth Radial canal
Circularcanal
5 cm
Open and Closed Circulatory Systems
• More complex animals have either open or closed circulatory systems
• Both systems have three basic components:– A circulatory fluid (blood or hemolymph)– A set of tubes (blood vessels)– A muscular pump (the heart)
LE 42-3
Hemolymph in sinusessurrounding organs
Heart
Anteriorvessel
Ostia
Tubular heart
An open circulatory system.
Lateralvessel
A closed circulatory system.
Auxiliary heartsVentral vessels
Dorsal vessel(main heart)
Small branch vesselsin each organ
Interstitialfluid
Heart
Hemolymph in sinusessurrounding organs
Heart
Anteriorvessel
Lateralvessel
Ostia
Tubular heart
• In insects, other arthropods, and most molluscs blood bathes the organs directly in an open circulatory system
• There is no distinction between blood and interstitial fluid, and this general body fluid is more correctly called hemolymph
• In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid
• Closed systems are more efficient at transporting circulatory fluids to tissues and cells– Oxygen travels via hemoglobin on blood
cells
Survey of Vertebrate Circulation• Humans and other vertebrates have a
closed circulatory system, often called the cardiovascular system
• Blood flows in a closed cardiovascular system, consisting of blood vessels and a two- to four-chambered heart
• Arteries carry blood AWAY from the heart and to capillaries, the sites of chemical exchange between the blood and interstitial fluid
• Veins return blood from capillaries INTO the heart
• Capillaries are very thin to allow gas exchange to occur
• Coronary blood vessels: provides the constant supply of oxygen and nutrients needed by the heart
Fishes
• A fish heart has two main chambers: one ventricle and one atrium
• Blood pumped from the ventricle travels to the gills, where it picks up O2 and disposes of CO2
Amphibians
• Frogs and other amphibians have a three-chambered heart: two atria and one ventricle
• The ventricle pumps blood into a forked artery that splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit
Reptiles (Except Birds)
• Reptiles have double circulation, with a pulmonary circuit (lungs) and a systemic circuit
• Turtles, snakes, and lizards have a three-chambered heart
Mammals and Birds
• In all mammals and birds, the ventricle is divided into separate right and left chambers
• The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood
• A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds
LE 42-4
FISHES
Gill capillaries
AMPHIBIANS
Lung and skin capillaries
REPTILES (EXCEPT BIRDS)
Lung capillaries
MAMMALS AND BIRDS
Lung capillaries
Gillcirculation
Heart:Ventricle (V)
Atrium (A)
Artery
VeinSystemic
circulation
Systemic capillaries Systemic capillaries
Systemiccircuit
Pulmocutaneouscircuit
Right Left
AA
V
A
V
A
V
Systemic capillaries
Right Left
Pulmonarycircuit
Rightsystemic aorta
V
A
V
Systemic capillaries
Right Left
Pulmonarycircuit
A
Systemiccircuit
Leftsystemic aorta
Systemic circuits include all body tissues except lungs. Note that circulatory systems are depicted as if the animal is facing you: with the right side of the heart shown at the left and vice-versa.
Concept 42.2: Double circulation in mammals depends on the anatomy and pumping cycle of the heart• The human
circulatory system serves as a model for exploring mammalian circulation
Mammalian Circulation: The Pathway
• Heart valves dictate a one-way flow of blood through the heart
• Blood begins its flow with the right ventricle pumping blood to the lungs
• In the lungs, the blood loads O2 and unloads CO2
• Oxygen-rich blood from the lungs enters the heart at the left atrium and is pumped to the body tissues by the left ventricle
• Blood returns to the heart through the right atrium
LE 42-5
Anteriorvena cava
Aorta
Right atrium
Right ventricle
Posteriorvena cava
Aorta
Capillaries ofabdominal organsand hind limbs
Pulmonaryvein
Pulmonaryvein
Left atrium
Left ventricle
Capillaries ofhead andforelimbs
Pulmonaryartery
Pulmonaryartery
Capillariesof right lung
Capillariesof left lung
Animation: Path of Blood Flow in Mammals
i
c
a
b
b’
b’
e e
ee
L
hL
L
LL
a
o
m q
g
d
fh
TO LUNGSTO LUNGS
FROM LUNGS
FROM LUNGS
FROM LOWER BODY
FROM UPPER BODY
TO LOWER BODY
Right Atrium
Left VentricleRight
Ventricle
Left Atrium
Pulmonary Arteries
TO UPPER BODY
Aorta
Aorta
Superior Vena Cava
Inferior Vena Cava
Pulmonary Veins Pulmonary
Veins