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

• 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

Mechanisms of Transport in Organisms (review)

Fick’s Law and Organisms

tc = L2

Ds

Average time for a molecule (solute, gas, or water) to move a set distance (L)...

Directly proportional to the distance squared!

p. 982

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

• How is hemolymph different from blood?• Describe the difference in fluid pressure and volume between open and closed circulatory systems.

See also p. 995

Structure of Blood Vessels

Compare pressures in arteries, veins, and capillaries.How is blood flow accomplished in veins?In which tissues would you expect to find the most capillaries?

p. 996

Bulk Flow

…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)

r4

8

p

xVolume flow rate =

in a cylinder

viscosity ( distance

pressure gradient

Jean Louis Marie Poiseuille (Poiseuille’s Law, ~1838)

Increase Flow?Increase radius…

How does this affect resistance?

Lower Viscosity… Is this a likely mechanism?

Increase Pressure… How would this be accomplished?

r4

8

p

xVolume flow rate =

viscosity ( distance

pressure gradient

Label the arrowsto show the netdirection of watermovement by1. hydrostatic(filtration) pressure1. osmosis

Label the diagram to explain the net direction of this bulk flow.

What conditionsmight change therate of filtration orosmosis?

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.

Which chamber receives blood first?

Evolution of the Vertebrate Heart

• Heart forms as a tube in all vertebrate embryos – with 4 “chambers” in a series:

(tail end) sinus venosus atrium ventricle truncus arteriosus (head end)

This is the circulatory scheme in bony fish

• In the embryo, contraction first begins in the ventricle. Why?– Later, the atria begin to beat, but at a

faster rate. Sig?

p. 998

Pumps in CirculationTwo 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?

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.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AnimalHearts.html

This group of marine invertebrates has solved the problem by having separate pumps:

* 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.

The Squid Hearts(cephalopods)

How does this adaptation relate to the lifestyle of cephalopods?

The Mammalian Cardiovascular

System

Trace the pathway of a singlered blood cell, beginning at theright atrium.

What causes the valves in the heart to close?

What mechanisms enable bloodto 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