1. Circulatory Systems The exchange of nutrients and wastes MUST
take place across _______ membranes
MOIST
(molecules must be dissolved to be transported across membranes)
One celled creatures:
Entire external surface exchanges with the environment
Simple Multiellular Organisms (like Sponges & Cnidarians)
All cells are exposed in some way to the environment.
But more complex organisms have cells which are isolated from their external environment… they need a…..
CIRCULATORY SYSTEM!!

2. The Presence of a Circulatory System:
Reduces the distance a substance must travel to enter or leave a cell.
Uses “Blood” to carry these molecules to the cells.
O2 diffuses from the air in the lungs (or similar structures) across epithelium to the “blood” which carries it to all parts of the body.
Once in the capillaries, O2 diffuses across epithelium again to the tissues.
CO2, of course, moves in the opposite direction.
There are 2 main types of Circulatory Systems:
OPEN & CLOSED

3. Open vs Closed Circulatory Systems
OPEN: Insects, most arthropods, mollusks
“hemolymph” (a combination of blood and interstitial fluid) bathes all the internal organs while moving through “sinuses”.
Circulation results from contraction of the “heart” and body movements.
Relaxation of the heart draws blood back through pores called “ostia”
YouTube Link
CLOSED: Annalids, some Mollusks, Chordates
Blood is confined to vessels, separated from interstitial fluid
Larger vessels branch into smaller
See transparencies….
Heart 
Arteries 
Arterioles 
Capillaries 
Venules 
Veins
(campbell activity)

4. Circulation & Blood: “LUB” “DUP!” Control of the heart
Cardiac cells are “MYOGENIC”:
Can contract without external
Input from the nervous system.
Tempo is controlled by the Sinoatrial node (S.A. node):
Located at right atrium by superior vena cava
“LUB”
Contraction at the SA node causes both atria to contract
Wave of contraction passes down to Atrioventricular (AV) node:
Impulse is delayed by 0.1 second (atria need to be empty)
“DUP!”
Causes ventricles to contract
Campbell Activity again....

5. Vessel Structure Epithelial tissue Smooth Muscle Connective Tissue
Simple squamous
Epithelial tissue
May only be just one
Single cell in capillaries!
Smooth Muscle
Thicker in the arteries than veins
Mostly elastic fibers
Connective Tissue
Also thicker in arteries….

6. Pressure & Flow: Law of Continuity: Pressure in the veins is near zero
Greatest in the Arteries
Lowest in the Veins
Law of Continuity:
Fluid will flow faster in narrower pipes.
Blood actually moves slower in capillaries because collectively they have greater total added diameter.
HOWEVER….
Pressure in the veins is near zero
The action of skeletal muscles (+ effect of the valves) is what actually keeps blood moving in veins.
BARORECPTOR REFLEX:
Vessels constrict in response to low blood pressure
…and dilate in response to rising blood pressure.
Only 5-10% of capillaries carry blood at any given time
Exceptions include BRAIN, HEART, LIVER, & KIDNEYS.
Hormonal signaling
Distribution is controlled by:
Precapillary sphincters

7. WebLinks