1. Explain Which groups of animals tend to have open circulatory systems and which have closed.
Compare and Contrast What is the major structural difference between vertebrates that have single loop circulatory systems and those that have double loop systems
Apply Concept Do you think large, active vertebrates would have been likely to succeed if closed circulatory systems had not evolved- explain

2. Ch 27 Animal Systems I
27.3 Circulation

3. Heart Hollow, muscular organ that pumps blood around the body
May have one or more
May be part of either an open or a closed circulatory system.

4. Open Circulatory Systems
Blood is only partially contained within a system of blood vessels
Arthropods and most mollusks have open circulatory systems.

5. One or more hearts or heartlike organs pump blood through vessels
Empty into a system of sinuses (spongy cavities) where blood comes into direct contact with body tissues.

6. Blood then collects in another set of sinuses and makes its way back to the heart.

7. Closed Circulatory Systems
Blood circulates entirely within blood vessels that extend throughout the body
Many larger, more active invertebrates, including annelids and some mollusks, and all vertebrates have closed circulatory systems.

8. Closed Circulatory Systems
Heart or heartlike organ forces blood through vessels
Nutrients and oxygen reach body tissues by diffusing across thin walls of capillaries
Pumped at higher pressure and circulates more efficiently.

9. Single-Loop Circulation
Single pump that forces blood around the body in one direction
Most vertebrates with gills.

10. Single-Loop Circulation
Atrium
Receives blood from the body
Ventricle
Pumps blood out of the heart and to the gills
Oxygen-rich blood travels from the gills to the rest of the body
Oxygen-poor blood then returns to the atrium.

11. Double-Loop Circulation
Two-pump circulatory system
Most vertebrates that use lungs
First loop is powered by one side of the heart
Forces oxygen-poor blood from the heart to the lungs.

12. Double-Loop Circulation
Blood picks up oxygen and drops off carbon dioxide in the lungs
Returns to the heart
Other side of the heart pumps oxygen-rich blood through the second circulatory loop to the rest of the body.

13. Amphibian hearts usually have three chambers: two atria and one ventricle
Left atrium receives oxygen-rich blood from the lungs
Right atrium receives oxygen-poor blood from the body
Both atria empty into the ventricle.

14. Reptilian hearts typically have three chambers: two atria and one ventricle
Have a partial partition in their ventricle
Less mixing of oxygen-rich and oxygen-poor blood than in amphibians.

15. Four-chambered hearts are actually two separate pumps working next to one another
Partitions evolved that divided the original two chambers into four, transforming one pump into two parallel pumps.