
How do simple organisms like jelly fish and
flat worms exchange reactants and products
of cellular respiration?
◦ Simple animals have a body wall that is only two
cells thick and that encloses a gastrovascular cavity
◦ This cavity functions in both digestion and
distribution of substances throughout the body
◦ Materials can diffuse in or out of the gastrovascular
cavity as needed.
Fig. 42-2
Circular
canal
Mouth
Pharynx
Mouth
Radial canal
(a) The moon jelly Aurelia, a cnidarian
5 cm
2 mm
(b) The planarian Dugesia, a
flatworm

How do more complex organisms exchanges the
reactants and products of cellular respiration?
◦ They have either an open or closed circulatory system.

How does an open circulatory system work?
◦ In insects, other arthropods, and most molluscs,
blood bathes the organs directly in an open
circulatory system
◦ In an open circulatory system, there is no
distinction between blood and interstitial fluid, and
this general body fluid is more correctly called
hemolymph

How does a closed circulatory system work?
◦ 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

What do we call our circulatory system?
◦ Humans and other vertebrates have a closed
circulatory system, often called the cardiovascular
system
◦ The three main types of blood vessels are arteries,
veins, and capillaries
Fig. 42-3
Heart
Hemolymph in sinuses
surrounding organs
Pores
Heart
Blood
Interstitial
fluid
Small branch vessels
In each organ
Dorsal vessel
(main heart)
Tubular heart
(a) An open circulatory system
Auxiliary hearts
Ventral vessels
(b) A closed circulatory system

What are the major components of the vertebrate
circulatory system?
◦ Arteries branch into arterioles and carry blood to
capillaries
◦ Networks of capillaries called capillary beds are the sites
of chemical exchange between the blood and interstitial
fluid
◦ Venules converge into veins and return blood from
capillaries to the heart
◦ Vertebrate hearts contain two or more chambers
◦ Blood enters through an atrium and is pumped out
through a ventricle
Fig. 42-4
Gill capillaries
Single circulatory
loop with a 2
chambered heart
Heart
Artery
Gill
circulation
Ventricle
Atrium
Vein
Systemic
circulation
Systemic capillaries
Fig. 42-5
Double circulation with
a 4 chambered heart
Double heart circulation
w/ 3 chambered
Amphibians
Reptiles (Except Birds)
Mammals and Birds
Lung and skin capillaries
Lung capillaries
Lung capillaries
Pulmocutaneous
circuit
Atrium (A)
Ventricle (V)
Right
systemic
aorta
Atrium (A)
Right
Systemic
circuit
Left
Systemic capillaries
Pulmonary
circuit
A
V
Right
Pulmonary
circuit
A
A
V
Left
Left
systemic
aorta
Systemic capillaries
Double circulation with a
3 chambered heart –
ventricle partially divided
A
V
V
Right
Left
Systemic
circuit
Systemic capillaries

How does blood flow in a mammal?
◦ 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 through the aorta to
the body tissues by the left ventricle
◦ The aorta provides blood to the heart through the
coronary arteries
◦ Blood returns to the heart through the superior vena
cava (blood from head, neck, and forelimbs) and
inferior vena cava (blood from trunk and hind limbs)
◦ The superior vena cava and inferior vena cava flow
into the right atrium
Fig. 42-6
Superior
vena cava
Capillaries of
head and
forelimbs
7
Pulmonary
artery
Pulmonary
artery
Capillaries
of right lung
Aorta
9
3
2
Capillaries
of left lung
3
4
11
Pulmonary
vein
Right atrium
1
Pulmonary
vein
5
Left atrium
10
Right ventricle
Left ventricle
Inferior
vena cava
Aorta
8
Capillaries of
abdominal organs
and hind limbs
Fig. 42-7
Pulmonary artery
Aorta
Pulmonary
artery
Right
atrium
Left
atrium
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Right
ventricle
Left
ventricle

How does the heart contract? What are the
two phases of the cardiac cycle?
◦ The contraction, or pumping, phase is called
systole
◦ The relaxation, or filling, phase is called diastole

What is another name for the heart rate?
◦ The heart rate, also called the pulse, is the number
of beats per minute
Fig. 42-8
2 Atrial systole;
ventricular
diastole
Semilunar
valves
closed
0.1 sec
AV
valves
open
1 Atrial and
ventricular
diastole
0.4 sec
Semilunar
valves
open
0.3 sec
AV valves
closed
3 Ventricular systole;
atrial diastole

What are the four valves in the heart called?
And what is their purpose?
◦ Four valves prevent backflow of blood in the heart
◦ The atrioventricular (AV) valves separate each
atrium and ventricle
◦ The semilunar valves control blood flow to the aorta
and the pulmonary artery
◦ The “lub-dup” sound of a heart beat is caused by
the recoil of blood against the AV valves (lub) then
against the semilunar (dup) valves

How does the heart maintain its rhythmic
beat?
◦ The sinoatrial (SA) node, or pacemaker, sets the
rate and timing at which cardiac muscle cells
contract
◦ Impulses from the SA node travel to the
atrioventricular (AV) node
◦ At the AV node, the impulses are delayed and then
travel to the Purkinje fibers that make the ventricles
contract
◦ The pacemaker (SA node) is influenced by nerves,
hormones, body temperature, and exercise
Fig. 42-9-5
1 Pacemaker
generates wave of
signals to contract.
SA node
(pacemaker)
ECG
2 Signals are
delayed at
AV node.
AV
node
3 Signals pass
to heart apex.
Bundle
branches
Heart
apex
4 Signals spread
throughout
ventricles.
Purkinje
fibers

How is the structure of blood vessels adapted
to transport material throughout the body?
◦ Capillaries have thin walls, the endothelium plus its
basement membrane, to facilitate the exchange of
materials
◦ Arteries and veins have an endothelium, smooth
muscle, and connective tissue
◦ Arteries have thicker walls than veins to
accommodate the high pressure of blood pumped
from the heart
◦ In the thinner-walled veins, blood flows back to the
heart mainly as a result of muscle action, valves
prevent back flow
Fig. 42-10
Artery
Vein
SEM
100 µm
Basal lamina
Endothelium
Smooth
muscle
Connective
tissue
Valve
Endothelium
Capillary
Smooth
muscle
Connective
tissue
Artery
Vein
Capillary
15 µm
Red blood cell
Venule
LM
Arteriole

How does blood flow change as it moves
from arteries to capillaries to veins?
◦ Blood flow is fast in arteries due to pumping of the
heart
◦ Blood flow slows in capillaries as the volume from
one artery spreads to feed an entire capillary bed –
this is good it slows things down and allows for
exchange of materials
◦ Blood flow increases slightly in veins due to
decreased surface area
Venae cavae
Veins
Venules
Capillaries
Arterioles
Arteries
120
100
80
60
40
20
0
Aorta
Velocity
(cm/sec)
50
40
30
20
10
0
Pressure
(mm Hg)
Area (cm2)
Fig. 42-11
5,000
4,000
3,000
2,000
1,000
0
Systolic
pressure
Diastolic
pressure

How can blood flow through capillaries be
controlled?
◦ Two mechanisms regulate distribution of blood in
capillary beds:
 Contraction of the smooth muscle layer in the wall
of an arteriole constricts the vessel
 Precapillary sphincters control flow of blood
between arterioles and venules
Fig. 42-15
Precapillary sphincters
Thoroughfare
channel
Capillaries
Arteriole
Venule
(a) Sphincters relaxed
Arteriole
(b) Sphincters contracted
Venule

Where does the critical exchange of nutrients
and gasses takes place in the circulatory
system?
◦ The critical exchange of substances between the
blood and interstitial fluid takes place across the
thin endothelial walls of the capillaries
◦ The difference between blood pressure and osmotic
pressure drives fluids out of capillaries at the
arteriole end and into capillaries at the venule end
Fig. 42-16
Body tissue
Capillary
INTERSTITIAL FLUID
Net fluid
movement out
Net fluid
movement in
Direction of
blood flow
Pressure
Blood pressure
Inward flow
Outward flow
Osmotic pressure
Arterial end of capillary
Venous end