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