Biology 2672a:
Comparative Animal
Physiology
Circulation
Why have a
circulatory system?
 Diffusion
sucks!
 Moves oxygen and
nutrients to cells
 Removes CO2 and waste
products from cells
How do I know it’s a circulatory
system?
 Pump
 Fluid
 Vessels
or spaces
Primitive circulatory systems
Open systems have all the
characteristics of a circulatory system
The vessels in open systems can
be quite elaborate…
Fig 24.24
Open Circulatory Systems
 Low
pressure
 Relatively inefficient
 Can’t keep interstitial fluids and
blood separate
 Don’t allow impressive athletic
feats
But what about insects?
 Insect
flight muscle has the
highest work output in living
organisms
 Oxygen delivery (via the
tracheal system) is decoupled
from the fluid circulatory system
Box 23.3
Closed Circulatory System
From Heart
To Heart
Fig 24.11
Flow Rate through a system
Flow
rate
Q = ΔP
R
P2
Equation 24.3
Difference in
pressure
between the
entry and exit to
the system
Resistance in
the system
P1
ΔP=P1-P2
Flow Rate
 Flow
Q = ΔP
R
rate can be determined by
Pressure at the start of the system
 Pressure loss in the system
 Resistance in the system

 Pressure
is proportional to both
flow rate and resistance
Resistance in a system
length
resistance
R=8Lη
4
πr
r
L
viscosity
radius
R
=
8
L
η
Resistance
4
π
r
Longer systems have more

resistance
 More viscosity = higher
resistance
 Resistance is proportional to
the 4th power of the radius of
the tube

A small change in tube diameter
= a huge change in resistance
A teleost heart
Fig. 24.14b
Fish circulatory system
Head
Body
Gills
Heart
Fig. 24.14a
What does this mean
physiologically?
3 kPa
Head
Body
Gills
Heart
Counter this with
relatively large
variation in heart size
and performance
5 kPa
Heart oxygen demand may be a
limiting factor in teleosts
Head
Body
Gills
Heart
High performance fish hearts
 Deoxygenated
blood perfusing
spongy myocardium is a limiting
factor for fish
 Salmonids, Tuna, Sharks have a
‘hybrid heart’.
Fig. 24.3c
(Most) Fishes Breathing Air
Plecostomus - Gut
Electric Eel - Mouth
Bowfin – Swim bladder
Fig. 23.15
(Most) Fishes breathing air
 No
change to heart design
 Air breathing organs usually in
parallel with body tissues
 Direct mixing of oxygenated and
deoxygenated blood

Ensures adequate O2 for the heart(?)
Frog heart
Moyes & Schulte Fig. 9.15b
Frog circulation
Selective
distribution of
oxygenated and
deoxygenated
blood
Moyes & Schulte Fig. 9.11c
Cephalopod Molluscs
 Radiated
200 Mya
 Have a closed, divided circulatory
system
Fig. 24.20a
Oxygenated
blood in heart
Oxygen delivery to octopus heart
muscle
Fig. 23.3d
Octopus circulation
 Two
branchial hearts, one
systemic
 Gills are in series with the
tissues
 Allows oxygenated blood to be
pumped at higher rate through
systemic tissues.
Circulation in mammals and
birds
Fig. 24.10a
An untwisted mammalian
circulatory system
Fig. 24.10b
End of material
for mid-term
exam
Reading for Thursday
 Regulation

of Circulation
Pp 611-641 (continued)