Transcript Circulation and Gas Exchange

Learning Objectives:
Circulation in Animals (2/20/09)
1. Compare the different methods of internal transport of
body fluids within the context of maintaining
homeostasis.
2. Differentiate between open and closed circulatory
systems, with examples.
3. Compare and contrast the structure and function of
mammalian arteries, veins and capillaries.
4. Discuss the forces involved in the exchange of materials
between capillaries and the interstitial fluid.
5. Describe the evolution of separate pulmonary and
systemic circuits in vertebrates.
6. Compare extrinsic and intrinsic regulation of cardiac
function.
This section begins on p. 994
Mechanisms of Transport
in Organisms (review)
• Diffusion, by molecular motion
– good only at short distances,
• Pump, Channel and Carrier mediated transport
– small molecules across membranes,
• Osmosis (water movement across membranes)
• Bulk Flow
– efficient large-scale, mass movement
– hydrostatic pressure
Fick’s Law and Organisms
Average time for a molecule (solute, gas, or water) to move
a set distance (L)...
Directly proportional
to the distance
squared!
tc =
p. 982
L2
Ds
The branching gastrovascular
cavity of Cnidaria
• Does this animal have
distinct boundary
organs?
•Name one other animal
that has a
gastrovascular cavity.
• Explain why Cnidaria
don’t need a separate
circulatory system.
Embryonic development of
circulatory systems in
invertebrates
Note that the coelom
in arthropods is
present, but much
reduced. Explain
why the coelom is
relatively large in
annelids.
Open vs. Closed Circulatory Systems
See also p. 995
• How is hemolymph different from blood?
• Describe the difference in fluid pressure and volume
between open and closed circulatory systems.
Structure of Blood Vessels
Compare pressures in arteries, veins, and capillaries.
p. 996
How is blood flow accomplished in veins?
In which tissues would you expect to find the most capillaries?
Bulk Flow
Jean Louis Marie Poiseuille (Poiseuille’s Law, ~1838)
…the concentrated movement of groups of molecules,
• in biological systems, most often in response to pressure
• directly proportional to the diameter of the tube and the pressure
gradient
• inversely proportional to the viscosity of the fluid and the distance the
fluid must travel (due to frictional forces)
Volume flow rate =
in a cylinder
viscosity (h)
pr4
DYp
8h
Dx
pressure gradient
distance
Increase Flow?
Increase radius…
How does this affect resistance?
Lower Viscosity…
Is this a likely mechanism?
Increase Pressure…
How would this be accomplished?
Volume flow rate =
viscosity (h)
pr4
DYp
8h
Dx
pressure gradient
distance
Label the arrows
to show the net
direction of water
movement by
1. hydrostatic
(filtration) pressure
1. osmosis
Label the diagram to
explain the net
direction of this
bulk flow.
What conditions
might change the
rate of filtration or
osmosis?
Do capillaries
ever change their
porosity?
Tissue Fluid Formation and Return
Transport across a capillary wall
Name one plasma protein that helps maintain the osmolarity of
blood plasma.
Evolution of the
Vertebrate Heart
• Heart forms as a tube in all vertebrate
embryos – with 4 “chambers” in a
series:
sinus venosus  atrium  ventricle
 truncus arteriosus (head end)
This is the circulatory scheme in bony fish
(tail end)
• In the embryo, contraction first begins Which chamber
receives blood
in the ventricle. Why?
– Later, the atria begin to beat, but at a
faster rate. Sig?
first?
p. 998
Pumps in Circulation
Two alternative methods, both create challenges:
• If the pump is used to deliver blood with force to the gas
exchange organ, little force remains to distribute the
oxygenated blood to the tissues.
•Name one type of animal with this circulatory scheme.
•How is the problem “handled”?
•If the pump is used to deliver blood with force to the
tissues, little force remains to send the deoxygenated blood
to the gas exchange organ.
•How have birds and mammals handled this problem?
Evolution of
pulmonary and
systemic circuits in
vertebrates
• How is the four chambered
heart in endotherms related to
temperature homeostasis?
• How is the function of the
pulmonary circuit different
from the function of the systemic
circuit?
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AnimalHearts.html
Most fishes have never solved this “problem”, which is
probably why most of them are poikilothermic with relatively
low aerobic capacity.
Venous return is facilitated by body movements.
While obviously adequate, this is not a very efficient system.
The pressure generated by contraction of the ventricle is
almost entirely dissipated when the blood enters the gills.
This group of marine
invertebrates has solved the
problem by having separate
pumps:
The Squid Hearts
(cephalopods)
* two gill (branchial)
hearts to force blood under
pressure to the gills
* a systemic heart to
force blood under pressure
to the rest of the body.
How does this adaptation relate to the lifestyle of cephalopods?
The Mammalian
Cardiovascular
System
Trace the pathway of a single
red blood cell, beginning at the
right atrium.
What causes the valves in the
heart to close?
What mechanisms enable blood
to be returned to the heart?
Cardiac cycle
Describe the mechanical (physical) events in one cardiac cycle.
What feature of heart muscle is necessary for this coordinated function?
The Cardiac Conduction System
Why are there nerves that innervate the heart?
What chemical messages affect heart action? p. 1002