Two Blood Circulation Systems
The blood is pumped around in two large “loops” within the body. One loop moves blood
around the body—to the head, limbs, and internal organs. The other loop moves blood to
and from the lungs where carbon dioxide is released and oxygen is picked up by the blood. A
simple version of these two “loops” is shown inFigure18.6. Systemic circulationis the
portion of the cardiovascular system which carries oxygen-rich blood away from the heart, to
the body, and returns oxygen-poor blood back to the heart. Thepulmonary circulationis
the part of the cardiovascular system which carries oxygen-poor blood away from the heart
to the lungs, and returns oxygen-rich blood back to the heart. This oxygen-rich blood then
gets pumped around the body in the systemic circulation. These two circulations will be
further discussed in Lesson 2.
Figure 18.6: The double circulatory system; blood in one circuit has to go through the heart
to enter the other circuit. ( 19 )
The Lymphatic System
Thelymphatic systemis a network of vessels and tissues that carry a clear fluid called
lymph.The lymphatic system, shown inFigure18.7, extends all around the body. Lymph
tissues include lymph nodes, lymph ducts, and lymph vessels. Lymph vessels are tube-
shaped just like blood vessels. The lymphatic system works with the cardiovascular system
to return body fluids to the blood. The lymphatic system and the cardiovascular system are
often called the body’s twocirculatory systems.
The lymphatic system has two main jobs: