Ch 27.3 Circulation
I.
Open and Closed Circulatory Systems:
Key Concepts:
1. In an open circulatory system, blood is only partially contained within a system of blood vessels as it
travels through the body.
2. In a closed circulatory system, blood circulates entirely within blood vessels that extend throughout
the body
3. Many animals move blood through their bodies using one or more hearts.
4. A heart is a hollow, muscular organ that pumps blood around the body.
5. A heart can be part of either an open or a closed circulatory system.
II.
Open Circulatory Systems
a. In an open circulatory system, blood is only partially contained within a system of blood vessels as it
travels through the body.
b. Arthropods and most mollusks have open circulatory systems.
c. One or more hearts or heart-like organs pump blood through vessels that empty into a system of
sinuses, or spongy cavities, where blood comes into direct contact with body tissues.
d. Blood then collects in another set of sinuses and makes its way back to the heart.
III.
Closed Circulatory Systems
a. In a closed circulatory system, blood circulates entirely within blood vessels that extend throughout
the body.
b. Many larger, more active invertebrates, including annelids and some mollusks, and all vertebrates
have closed circulatory systems.
c. A heart or heart-like organ forces blood through vessels.
d. Nutrients and oxygen reach body tissues by diffusing across thin walls of capillaries, the smallest
blood vessels.
e. Blood that is completely contained within blood vessels can be pumped under higher pressure and
circulated more efficiently than can blood in an open system.
IV.
IV. Single- and Double-Loop Circulation – Key Concepts
a. Most vertebrates with gills have a single-loop circulatory system with a single pump that forces
blood around the body in one direction.
b. Most vertebrates that use lungs for respiration have a double-loop, two-pump circulatory system.
V.
Single –Loop Circulation
a. Most vertebrates with gills have a single-loop circulatory system
with a single pump that forces blood around the body in one
direction.
b. In fishes, for example, the heart consists of two chambers: an
atrium and a ventricle.
i. The atrium receives blood from the body.
ii. The ventricle then pumps blood out of the heart and to
the gills.
iii. Oxygen-rich blood travels from the gills to the rest of the
body. Oxygen-poor blood then returns to the atrium.
VI.
Double-Loop Circulation
a. Most vertebrates that use lungs for respiration have a doubleloop, two-pump circulatory system.
i. 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.
ii. After the blood picks up oxygen and drops off carbon
dioxide in the lungs, it returns to the heart.
iii. The other side of the heart pumps oxygen-rich blood
through the second circulatory loop to the rest of the
body.
Comparing Heart Chambers – Amphibians & Reptiles
a. Amphibian hearts usually have three chambers: two atria and one ventricle.
b. Reptilian hearts, like that of this crocodile, typically have three chambers: two atria and one
ventricle.
c. 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.
Mammalian Heart Chambers
a. Four-chambered hearts are actually two separate pumps
working next to one another.
b. Partitions divide the two chambers into four, transforming one
pump into two parallel pumps.
c. The partitions also separated oxygen-rich blood from oxygenpoor blood.
VII.
VIII.