Chapter 42

ultimately occur at the cellular level.
In unicellular organisms, these exchanges

the environment is not possible.
Gills are an example of a

small and/or thin animals, cells can exchange materials directly with

that is only two cells thick and that encloses a

The moon jelly Aurelia, a cnidarian
The planarian Dugesia, a
flatworm
(b)
Mouth
Pharynx
2 mm
5

or closed circulatory systems.
Both systems have three basic components:
A circulatory

organs directly in an open circulatory system.
In an open circulatory

vessels and is distinct from the interstitial fluid.
Closed systems are

circulatory systems
Heart
Hemolymph in
sinuses
surrounding organs
Heart
Interstitial
fluid
Small branch vessels
In each organ
Blood
Dorsal vessel
(main

Auxiliary hearts

Ventral vessels

(b) A closed circulatory system

(a) An open circulatory system

Tubular heart

Pores

a closed circulatory system, often called the cardiovascular system.
The three

of capillaries called capillary beds are the sites of chemical

atrium and is pumped out through a ventricle.

a two-chambered heart.
In single circulation, blood leaving the heart passes

blood are pumped separately from the right and left sides

capillaries
Reptiles


Lung capillaries
Pulmonary
circuit
Right
systemic
aorta
Right
Left
Left
systemic
aorta
Systemic capillaries
A
A
V
V
Systemic

Pulmonary
circuit

Systemic
circuit

Right

Left

A

A

V

V

Lung capillaries

Mammals and
Birds

circuit to pick up oxygen through the lungs.
In amphibians, oxygen-poor

heart: 2 atria and 1 ventricle.
The ventricle pumps blood

two atria and one ventricle.
In alligators, caimans, and other crocodilians

two atria and two ventricles.
The left side of the heart

RA --> RV --> LUNGS --> LA --> LV --> Body

begins its flow with the right ventricle pumping blood to

(deoxygenated blood from head, neck, and forelimbs) and inferior vena

blood from
body to heart RA
Pulmonary artery
Capillaries
of right Lung
GAS EXCHANGE
3
7
3
8
9
2
4
11
5
1
10
Aorta
Pulmonary vein

Right Ventricle
RV - Pumps blood to lungs

Inferior vena cava
Returns deoxygenated blood from
body to heart RA

Capillaries of
abdominal organs and hind limbs
EXCHANGE with body cells

Pulmonary vein
Carries oxygenated blood
to heart: LA

Left Atrium - LA
Receives oxygenated blood
from lungs

Left Ventricle - LV
Pumps oxygenated blood to body

Aorta = main artery to body
for Systemic Circulation

Capillaries
of left Lung
GAS EXCHANGE

Pulmonary artery
Carries deoxygenated blood to lungs

Capillaries of head and
Forelimbs - EXCHANGE

mammalian heart provides a better understanding of double circulation.
RIGHT side

lungs
Right Atrium RA
Receives
Deoxygented
Blood from
body
Semilunar
valve
Atrioventricular
valve
Right Ventricle RV
Pumps to lungs

Left Ventricle LV
Pumps oxygenated
blood to body via aorta

Atrioventricular
valve

Left Atrium LA
Receives oxgenated
blood from lungs

Semilunar
valve

Pulmonary veins -
from lungs to heart

Aorta - systemic
circulation

the cardiac cycle.
The contraction, or pumping, phase is called systole.
The

of beats per minute.
The stroke volume is the amount of

(AV) valves separate each atrium and ventricle.
The semilunar valves control

= they contract without any signal from the nervous system.
The

contract
Pacemaker
generates wave of
signals to contract.
1
SA node
(pacemaker)
ECG
Signals are
delayed at
AV node.
2
AV
node
Signals pass
to

3

Bundle
branches

Heart
apex

arrangement of blood vessels
The physical principles that govern movement of

to facilitate the exchange of materials.
Arteries and veins have an

affect blood flow and blood pressure.
Velocity of blood flow is

velocity, and blood pressure.
5,000
4,000
3,000
2,000
1,000
0
0
50
40
30
20
10
120
80
100
60
40
20
0
Area (cm2)
Velocity
(cm/sec)
Pressure
(mm Hg)
Aorta
Arteries
Arterioles
Capillaries
Venules
Veins
Venae cavae
Diastolic
pressure
Systolic
pressure

against the wall of a vessel.
In rigid vessels blood pressure

the pressure in the arteries during ventricle contraction /systole; it

and peripheral resistance due to constriction of arterioles.
Vasoconstriction is the

body’s demands change.
The peptide endothelin is an important inducer of

Pressure in cuff
greater than
120 mm Hg

Rubber
cuff
inflated
with air

Artery
closed

120

120

Pressure in cuff
drops below
120 mm Hg

Sounds
audible in
stethoscope

Pressure in
cuff below
70 mm Hg

70

Blood pressure reading: 120/70

Sounds
stop

with longer necks require a higher systolic pressure to pump

(open)
Skeletal muscle
Valve (closed)

Blood supply varies in many other sites.
Two mechanisms regulate distribution

fluid takes place across the thin endothelial walls of the

fluid
movement out
Direction of
blood flow
Net fluid
movement in
Blood pressure = hydrostatic pressure
Inward

Outward flow

Osmotic pressure

Arterial end of capillary

Venous end

Pressure

fluid that leaks out in the capillary beds … restoring

and filter lymph - an important role in the body’s

cells suspended in a liquid matrix called plasma.
The cellular elements:

electrolytes)
Osmotic balance,
pH buffering, and
regulation of
membrane
permeability
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Osmotic balance
pH buffering
Clotting
Defense
Plasma proteins
Albumin
Fibrinogen
Immunoglobulins
(antibodies)
Substances transported by

Nutrients (such as glucose, fatty acids, vitamins)
Waste products of metabolism
Respiratory gases (O2 and CO2)
Hormones

Separated
blood
elements

Cellular elements 45%

Cell type

Functions

Number
per µL (mm3) of blood

Erythrocytes
(red blood cells)

5–6 million

Transport oxygen
and help transport
carbon dioxide

Leukocytes
(white blood cells)

5,000–10,000

Defense and
immunity

Basophil

Neutrophil

Eosinophil

Lymphocyte

Monocyte

Platelets

Blood clotting

250,000–
400,000

salts in the form of dissolved ions, sometimes called electrolytes.
Another

blood cells rbc = erythrocytes, transport oxygen.
White blood cells wbc

numerous blood cells.
They transport oxygen throughout the body.
They contain hemoglobin,

Erythrocytes - Oxygen Transport

cells, or leukocytes: monocytes, neutrophils, basophils, eosinophils, and lymphocytes.
They function

in blood clotting.
When the endothelium of a blood vessel is

from:
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Prothrombin
Thrombin
Fibrinogen
Fibrin
5 µm
Fibrin clot
Red blood

Blood clotting

of blood wear out and are replaced constantly throughout a

cells
Erythrocytes
Platelets
Neutrophils
Basophils
Eosinophils
Monocytes

Vessels
One type of cardiovascular disease, atherosclerosis, is caused by the

to atherosclerosis.
Low-density lipoproteins (LDLs) = “bad cholesterol,” are associated with

for cellular respiration and disposes of carbon dioxide. Gases diffuse

of O2, or respiratory medium.
In a given volume, there

gases between their cells and the respiratory medium, either air

surface area for gas exchange
Parapodium (functions as gill)
(a) Marine worm
Gills
(b)

(c) Sea star

Tube foot

Coelom

Gills

move through water or move water over their gills for

blood
Fluid flow
through
gill filament
Lamella
Blood flow through
capillaries in lamella
Water flow
between
lamellae
Countercurrent exchange
PO2 (mm

PO2 (mm Hg) in blood

Net diffusion
of O2from
water to
blood

150

120

90

60

30

110

80

20

Gill filaments

50

140

tiny branching tubes that penetrate the body.
The tracheal tubes supply

Body wall
Trachea
Air external openings

system (open or closed) transports gases between the lungs and

/ air tubes conveys air to the lungs.
Air inhaled through

of Air
Amphibians, such as a frog, ventilates its lungs by

cage gets
smaller as
rib muscles
relax
Air
exhaled
EXHALATION
Diaphragm relaxes
(moves up)
Volume decreases
Pressure increases
Air rushes out
INHALATION
Diaphragm

that function as bellows that keep air flowing through the

empty;
Lungs Fill
INHALATION
Air sacs fill

centers are in two regions of the brain, the medulla

CO2 concentrations in the blood.
These sensors exert secondary control over

gases
The metabolic demands of many organisms require that the blood

= 40
PO2 = 100
PO2 = 100
PO2 = 40
Circulatory
system
Body tissue
PO2 ≤

PCO2 ≥ 46 mm Hg

Body tissue

PCO2 = 46

PCO2 = 40

PCO2 = 40

PCO2 = 46

Circulatory
system

PCO2 = 40 mm Hg

Alveolus

(b) Carbon dioxide

(a) Oxygen

the amount of oxygen that blood can carry.
Arthropods and many

hemoglobin dissociation curve shows that a small change in the

tissues
during exercise
100
40
0
20
60
80
0
40
80
100
O2 saturation of hemoglobin (%)
20
60
Tissues during
exercise
Tissues
at rest
Lungs
PO2 (mm Hg)
(a)

O2 saturation of hemoglobin (%)

40

0

20

60

80

0

40

80

100

20

60

100

PO2 (mm Hg)

(b) pH and hemoglobin dissociation

pH 7.4

pH 7.2

Hemoglobin
retains less
O2 at lower pH
(higher CO2
concentration)

buffering.
CO2 from respiring cells diffuses into the blood and is

fluid
Plasma
within capillary
CO2
CO2
CO2
Red
blood
cell
H2O
H2CO3
Hb
Carbonic acid
Hemoglobin
picks up
CO2 and H+
CO2 transport
to lungs
HCO3–
Bicarbonate
H+
+
Hemoglobin
releases
CO2 and H+
To

HCO3–

HCO3–

Hb

H+

+

HCO3–

H2CO3

H2O

CO2

CO2

CO2

CO2

Alveolar space in lung

allow them to perform extraordinary feats.
The extreme O2 consumption of

veins
Pulmonary arteries
Systemic veins
Systemic arteries
Heart
Systemic
capillaries
CO2
O2
CO2
O2
Body tissue - GAS EXCHANGE

closed circulatory systems.
Compare and contrast the circulatory systems of fish,

node.
Relate the structures of capillaries, arteries, and veins to their

to the circulatory system.
Describe the function of erythrocytes, leukocytes,

and in tissues.
Draw and explain the hemoglobin-oxygen dissociation curve.