http://www.ck12.org Chapter 1. Human Biology
1.22 Circulation and the Lymphatic System
- Explain how the cardiovascular and the lymphatic systems work together.
Are your blood vessels leaky?
None of your blood vessels are leaking this badly, or you’d be in the hospital! But your blood vessels do leak a
little bit. Water and solutes pass out of the blood vessels and help form the fluid that bathes your body’s tissues.
Ultimately the fluid that is lost from the blood vessels is returned through the lymphatic system.
The Lymphatic System and Circulation
Thelymphatic systemis a network of vessels and tissues that carry a clear fluid calledlymph. The lymphatic
system (Figure1.39) spreads all around the body. Lymph vesselsare 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 two "circulatory systems."
Role of the Lymphatic System in Circulation
You may think that your blood vessels have thick walls without any leaks, but it’s not true. Blood vessels can leak
just like any other pipe. The lymphatic system makes sure leaked blood returns back to the bloodstream.
When a small amount of fluid leaks out from the blood vessels, it collects in the spaces between cells and tissues.
Some of the fluid returns to the cardiovascular system, and the rest is collected by the lymph vessels of the lymphatic
system (Figure1.40). The fluid that collects in the lymph vessels is called lymph. The lymphatic system then returns
the lymph to the cardiovascular system. Unlike the cardiovascular system, the lymphatic system is not closed and
has no central pump (or heart). Lymph moves slowly in lymph vessels. It is moved along in the lymph vessels by
the squeezing action of smooth muscles and skeletal muscles.