1. Introduction to Circulation
AP Biology
Unit 6

2. Invertebrates with Gastrovascular Cavities
Don’t have a true circulatory system
Material exchange (gases, nutrients, wastes) with the environment occurs through diffusion
Why is diffusion effective here?
The animals are only a few cell layers thick– materials don’t have to go across too many layers
Example: Cnidarians
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3. True Circulatory Systems
3 main components in a true circulatory system:
Circulatory fluid (blood)
Tubes to transport fluid (blood vessels)
Muscular pump (heart)
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4. True Circulatory Systems
Blood pressure keeps the circulatory fluid moving through the system (in addition to other forces)
Blood pressure = force exerted on the walls of the blood vessels by the blood (caused primarily by the pumping of the heart)
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5. True Circulatory Systems
In general, higher metabolism means a more complex circulatory system
An animal either has an open or a closed circulatory system
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6. Open Circulatory Systems
Blood and interstitial fluid are the same (hemolymph)
Low blood pressure (less energy to circulate fluid)
Simple system of tubes
sinuses = spaces between organs
ostia = tubes that open to the body environment
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7. Open Circulatory System
The heart helps pump hemolymph around
Hemolymph will also be pushed back into the ostia as the animal moves around
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8. Closed Circulatory System
Blood is confined to tubes, so it is different from interstitial fluid
Molecules diffuse between blood and interstitial fluid
High blood pressure
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9. Question… Why would higher blood pressure be beneficial?
Can get blood to areas that need it more efficiently
Allows the organism to be more active
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10. Closed Circulatory System
Complex system of tubes
arteries = vessels that carry blood from heart to capillaries (throughout body)
veins = vessels that carry blood from capillaries to heart (in general)
capillaries = tiny, porous vessels through which molecules diffuse in / out (throughout body)
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11. General Circulatory Pathway
Heart  artery  capillaries  vein  back to heart
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12. Comparison of Vertebrate Circulation- Fish
Gas exchange with the environment occurs in the gills
Blood pressure is highest in the artery leaving the heart to go to the lungs.
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13. Comparison of Vertebrate Circulation- Fish
Blood in the heart is separated (oxygenated and de-oxygenated blood are not mixed together)
Single circulation = blood goes to the heart once (continues on to the body without returning after the lungs)
2 chambers in heart (1 atrium, 1 ventricle)
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14. Comparison of Vertebrate Circulation- Amphibian
Gases are exchanged with the environment in the lungs and across the skin
Blood pressure is highest where blood leaves the heart
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15. Comparison of Vertebrate Circulation- Amphibian
Blood in the heart is mixed– deoxygenated and newly oxygenated blood mix together in ventricle
Double circulation = blood is pumped two times from the heart– goes to the lungs, then comes back to get pumped to the rest of the body
3 chambers in heart (2 atria, 1 ventricle)
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16. Comparison of Vertebrate Circulation- Reptile
Gas exchange occurs in the lungs
Blood pressure is where blood is leaving the heart
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17. Comparison of Vertebrate Circulation- Reptile
Blood in the heart is mixed-- deoxygenated and newly oxygenated blood mix together in partially separated ventricle
Double circulation
3 ½ chambers in heart (2 atria, one partially separated ventricle)
Only crocodiles have fully separated ventricles
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18. Question…
What is the benefit of having double circulation (compared to single circulation)?
Blood can reach tissues more efficiently  High blood pressure\
This allows the organism to be more active
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19. Reptile Circulation Reptiles also have a 2nd aorta Benefit?
Can bypass the lungs when underwater (no point in sending blood to the lungs if there can’t get O2 from them)
Blood continues to flow to the body tissues (so they can still get some O2)  higher activity
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20. Comparison of Vertebrate Circulation- Mammal & Bird
Gas Exchange occurs in the lungs
Blood pressure is where blood is leaving the heart
Blood is separated – deoxygenated and newly oxygenated blood do not mix (held in separate chambers)
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21. Comparison of Vertebrate Circulation- Mammal & Bird
Double circulation
4 chambers in heart (2 atria, 2 ventricles)
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22. Question…
Why is having separated (compared to mixed blood) an advantage?
If blood is mixed, then deoxygenated blood that hasn’t gone to the lungs will also return to the body
Separated blood means that the blood returning to the body is all fully re-oxygenated
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23. Pressure and Metabolism
The inability to maintain pressure over a distance yields lower metabolism.
Pressure decreases as blood flows through tiny capillaries
Which organism can have the highest metabolic rate?
Mammals and birds (in general)
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24. Mammalian Heart 4 chambered heart (2 atria, 2 ventricles)
Right side
Left side
4 chambered heart (2 atria, 2 ventricles)
Valves = flaps that keep chambers of the heart closed at the right time
Valves are needed to build pressure in heart and prevent back-flow of blood.
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25. Atrioventricular (AV) Valves
Located between the atria and ventricles
Tricuspid Valve
Between the right atrium and right ventricle
3 flaps
Bicuspid (Mitral) valve
Between the left atrium and left ventricle
2 flaps
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26. Semilunar valves located at two exits for the heart
Between the right ventricle and the pulmonary artery (to lungs)
Between the left ventricle and the aorta (to the body)
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27. Pathway of Blood
Do you remember the pathway of blood through the body and the heart?
Use these terms: Right Atrium, Left Atrium, Right Ventricle, Left Ventricle, Pulmonary Artery, Pulmonary Vein, Aorta, Lung Capillaries, Capillaries in Top or Bottom of Body, Anterior / Posterior Vena Cava
Start where the blood first leaves the heart to go to the body
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28. Pathway of blood
Aorta  arteries  capillaries in body  veins  vena cava  right atrium  right ventricle  pulmonary artery  lung capillaries  pulmonary vein  left atrium  left ventricle  aorta
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29. Questions… Where does the blood have the highest O2 concentration?
Just after leaving lungs (where it picked up O2)
Where does the blood have the highest CO2 concentration?
Just before getting to the lungs (hasn’t dropped off the CO2 waste yet)
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30. Heartbeat
The heart beat is controlled by electrical signals generated in specific cells in the heart = self excitation
Sinoatrial (SA) node = a group of specialized cells that initiates the heartbeat
Also called the pacemaker of the heart
generates electrical impulses that cause both atria to contract
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31. Heartbeat Atrioventricular (AV) node
When it receives the signals from the SA node, it transfers the signals to the Bundle of His
Bundle of His spreads the signal to the Purkinje fibers in the ventricles  both ventricles contract
Pathway:
SA  AV 
Bundle of His
 Purkinje
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