1. Lesson Overview
27.3 Circulation

2. THINK ABOUT IT How do energy and nutrients get to your body cells?
How does oxygen from your lungs get to your brain and the rest of your body?
How do carbon dioxide and wastes generated within your body get eliminated?

3. Open and Closed Circulatory Systems
Many animals move blood through their bodies using one or more hearts.
A heart is a hollow, muscular organ that pumps blood around the body.
A heart can be part of either an open or a closed circulatory system.

4. Open Circulatory Systems
In an open circulatory system, blood is only partially contained within a system of blood vessels as it travels through the body.
Arthropods and most mollusks have open circulatory systems.

5. Open Circulatory Systems
One or more hearts or heartlike organs pump blood through vessels that empty into a system of sinuses, or spongy cavities
Blood then collects in another set of sinuses and makes its way back to the heart.

6. Closed Circulatory Systems
In a closed circulatory system, blood circulates entirely within blood vessels.
Many larger, more active invertebrates, including Earthworms & some mollusks, and all vertebrates have closed circulatory systems.
A heart or heartlike organ forces blood through vessels.

7. Open and Closed Circulatory Systems
How do open and closed circulatory systems compare?

8. Open and Closed Circulatory Systems
How do open and closed circulatory systems compare?
In an open circulatory system, blood is only partially contained within a system of blood vessels as it travels through the body.
In a closed circulatory system, blood circulates entirely within blood vessels that extend throughout the body.

9. Open and Closed Circulatory Systems
How do open and closed circulatory systems compare?

10. Open and Closed Circulatory Systems
How do open and closed circulatory systems compare?

11. Single-Loop Circulation
Most vertebrates with gills have a single-loop circulatory system with a single pump that forces blood around the body in one direction.
In fishes, for example, the heart consists of two chambers: an atrium and a ventricle.

12. Single-Loop Circulation
The atrium receives blood from the body.
The ventricle then 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.

13. Double-Loop Circulation
Most vertebrates that use lungs for respiration have a double-loop, two-pump circulatory system.
The first loop of the circulatory system is powered by one side of the heart and forces oxygen-poor blood from the heart to the lungs.

14. Mammalian Heart-Chamber Evolution
Amphibian hearts usually have 3 chambers: two atria and one ventricle.
Some mixing of oxygen-rich and oxygen-poor blood does occur, but the internal structure of the ventricle directs blood flow so that most oxygen-poor blood goes to the lungs and most oxygen-rich blood goes to the rest of the body.

15. Mammalian Heart-Chamber Evolution
Reptilian -three chambers: two atria and one ventricle.
Most reptiles have a partial partition in their ventricle, resulting in less mixing of oxygen-rich and oxygen-poor blood than there is in amphibian hearts.

16. Mammalian Heart-Chamber Evolution
Four-chambered hearts like those in modern mammals are actually two separate pumps working next to one another.
During chordate evolution, partitions evolved that divided the original two chambers into four, transforming one pump into two parallel pumps.
The partitions also separated oxygen-rich blood from oxygen-poor blood.

17. Single- and Double-Loop Circulation
How do the patterns of circulation in vertebrates compare?

18. Single- and Double-Loop Circulation
How do the patterns of circulation in vertebrates compare?
Most vertebrates with gills have a single-loop circulatory system with a single pump that forces blood around the body in one direction.
Most vertebrates that use lungs for respiration have a double-loop, two-pump circulatory system.