AP Biology
Unit 6

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 main components in a true circulatory system:
1. Circulatory fluid (blood)
2. Tubes to transport fluid (blood vessels)
3. Muscular pump (heart)
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• 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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• 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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• 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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• The heart helps pump hemolymph around
• Hemolymph will also be pushed back into the ostia as the animal moves around
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• 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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• 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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• 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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• Heart  artery
 capillaries
 vein
 back to heart
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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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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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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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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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Comparison of Vertebrate
Circulation- Reptile
• Gas exchange occurs in the lungs
• Blood pressure is where blood is leaving the heart
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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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• 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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Reptile Circulation
• Reptiles also have a 2 nd aorta
• Benefit?
– Can bypass the lungs when underwater (no point in sending blood to the lungs if there can’t get O
2 from them)
– Blood continues to flow to the body tissues (so they can still get some O
2
)
 higher activity
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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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Comparison of Vertebrate
Circulation- Mammal & Bird
• Double circulation
• 4 chambers in heart (2 atria, 2 ventricles)
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• 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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• 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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Right 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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Left side

• 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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• 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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• 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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• 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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• Where does the blood have the highest O
2 concentration?
– Just after leaving lungs (where it picked up O
2
)
• Where does the blood have the highest CO
2 concentration?
– Just before getting to the lungs (hasn’t dropped off the CO
2 waste yet)
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• 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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• 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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