Circulation
Systems of transport within bodies
Hannah Nevins
Bio 1b Spring 2009
Transportation to and from cells
 Nutrients – e.g. fatty




acids, glucose
Metabolites – wastes
Hormones – signaling
cells, organs
Gases – O2, CO2
How are gases carried?
Circulatory System Components:
 Circulatory fluid – carry
solutes, gases, immune
cells, RBCs
 Vessels – “roads” for
transport
 Pump – to move fluid
 Valves – to keep flow
unidirectional (why?)
Cell Types: Red &
White
Components of (vertebrate) blood
Simple Circulation: Ciliated Systems
 Bodies <1 mm don’t need a complex system
 Why not?
 Gastrovascular system is used for circulation
 Cnidarians  Platyhelminthes –
 Ciliated digestive cavity with branching extensions
Open Circulatory System:
 E.g. Arthropods,
Molluscs
 Hemolymph is fluid
 Fluid exits dorsal vessel
– returns via ostia
(veins)
 Drawbacks:
 Backwaters & eddies
 Not efficient
 Poor oxygenation
 Poor diffusion gradients
 How can it be
improved?
Open Circulatory System:
 Hemolymph is fluid
 Fluid exits dorsal vessel
– returns via ostia
(veins)
 Drawbacks:
 Backwaters & eddies
 Not efficient
 Poor oxygenation
 Poor diffusion gradients
 How could this system
be improved?
Open
Closed
Closed Circulatory System:
 More efficient circulation =
higher activity levels
 Some invertebrates
 Annelids - have multiple
hearts
 Cephalopods – 3 hearts: one
to each gill and 1 for body
Hemodynamics:
 Capillaries greatly
increase area –
 Is this important? Why?
 Velocity changes with
distance from heart
 High resistance in
capillaries
 Pressure varies with
cardiac output
**watch movie
Venous flow – helped by
muscle action
Fish
 Two-chambered heart
Drawbacks:
 Systemic blood is not
pressurized
 As heart works harder, it
gets blood that has
reduced O2
Amphibians & some Reptiles
 Two atria & 1 ventricle
 Blood mixed in ventricle
 Greater systemic pressure =
> higher activity levels
 Heart gets fresher blood
-Which of these has a greater
density of skin capillaries?
Why?
Variations in the circulatory system:
Four-chamber heart: Crocodiles, Birds
and Mammals
 No mixing of oxygenated and deoxygenated blood
What is the advantage of this?
Human Circulation:
Capillaries are everywhere!
 2000/ mm2, usually
<2% open
 Surface area = 1000 sq.
miles!!
 (SC Co = 446 sq. mi.)
Capillary action
 One-celled thick
 -leaky
 Allows for diffusion of
nutrients & gases
 Hydrostatic pressure
forces blood out…
Capillary action
 One-celled thick
 -leaky
 Allows for diffusion of
nutrients & gases
 Hydrostatic pressure
forces blood out
 Osmotic pressure
recaptures it
 Lymph system captures
the rest…