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Circulation and the Lymphatic System

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Circulation and the Lymphatic System

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

The lymphatic system is a network of vessels and tissues that carry a clear fluid called lymph. The lymphatic system ( Figure below ) spreads all around the body and filters and cleans the lymph of any debris, abnormal cells, or pathogens. Lymph vessels are tube-shaped, just like blood vessels, with about 500-600 lymph nodes (in an adult) attached. 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."

Organs of the lymphatic system include the tonsils, thymus gland and spleen. The thymus gland produces T cells or T-lymphocytes (see below) and the spleen and tonsils help in fighting infections. The spleen’s main function is to filter the blood. The spleen also detects viruses and bacteria and triggers the release of pathogen fighting cells.

The lymphatic system helps return fluid that leaks from the blood vessels back to the cardiovascular system.

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 ( Figure below ). 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 (meaning it is an open circulatory system that releases and collects fluid) 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.

Lymph capillaries collect fluid that leaks out from blood capillaries.

Role of the Lymphatic System in the Body’s Defenses

The lymphatic system also plays an important role in the immune system. For example, the lymphatic system makes white blood cells that protect the body from diseases. Cells of the lymphatic system produce two types of white blood cells, T cells and B cells, that are involved in fighting specific pathogens. Lymph nodes, which are scattered throughout the lymphatic system, act as filters or traps for foreign particles and are important in the proper functioning of the immune system. The role of the lymphatic system in the immune response is discussed in additional concepts.

Vocabulary

  • lymph : Clear fluid that drains through the lymphatic system and into the bloodstream.
  • lymph vessel : Thin-walled tube that carries the lymph through the lymphatic system.
  • lymphatic system : Network of vessels that carry a clear fluid called lymph; lymphatic organs also play a role in the immune system.

Summary

  • The lymphatic system works with the cardiovascular system to return body fluids to the blood.
  • The lymph, the clear liquid found in the lymphatic system, is moved along in the lymph vessels by the squeezing action of smooth muscles and skeletal muscles.

Practice

Use the resource below to answer the questions that follow.

  1. Where are lymphatic vessels found?
  2. What are the functions of the lymphatic system?
  3. What is interstitial fluid?
  4. What causes circulation in the lymphatic system?
  5. What are the functions of lymph nodes?
  6. What effect does removing a person's spleen have on the functioning of the body?

Review

  1. How does the lymph circulate through the body?
  2. Where does lymph come from?

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