What is a Lymph? - Definition & Anatomy

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  • 0:00 Definition of Lymph
  • 0:45 Formation & Recovery
  • 2:45 Lymph Composition
  • 4:30 Lesson Summary
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Lesson Transcript
Instructor: Stephen Christensen
In this lesson, you will learn about lymph, a fluid that forms in your body's tissues. You will explore how lymph is produced, how it moves through your body, and why it is important to your overall health. A post-lesson quiz will test your knowledge.

Definition of Lymph

Lymph is an alkaline fluid that originates as interstitial fluid in your body. In this context, an interstitial space is basically an empty space between tissue structures. Interstitial fluid flows in the space between and around tissues and cells. You might compare this space to the holes in a sponge. Just as these holes fill up with water and keep the material of a sponge wet, the fluid that becomes lymph bathes and nourishes in the cells of all your tissues.

Lymph is collected within lymphatic vessels, which carry it away from your tissues and eventually return it to your bloodstream. Lymph helps clear your body of cellular wastes and infectious organisms. Chyle, a specialized version of lymph, transports fats from your intestine to your bloodstream.

Formation & Recovery

In order to move blood through your arteries and veins, your heart must apply a certain amount of pressure with each beat. This pressure is transmitted through your arteries to your capillaries, which are very thin-walled, leaky vessels where oxygen, nutrients, and fluids are delivered to the cells of your body. As fluid leaks from the capillaries and infiltrates into the surrounding tissues, it becomes interstitial fluid.

If interstitial fluid wasn't recovered, your tissues would soon drown in the excess, and the blood within your arteries and veins would become increasingly concentrated due to continual loss of fluid. Neither of these events is desirable, so your body has devised a system to return interstitial fluid to your bloodstream.

Scattered within the networks of blood capillaries throughout your body are lymphatic capillaries, which are porous and leaky, tiny tubules. The pressure in the lymphatic capillaries is lower than in the blood capillaries and the surrounding tissues, so the fluid leaking out of your blood capillaries tends to move into the lymphatic capillaries, much like the water in a river runs downhill.

Mirroring the blood capillaries, which join to become venules and then veins before returning to your heart, your lymphatic capillaries join into progressively larger lymphatic vessels that carry lymph away from your tissues and transport it toward the center of your body.

Lymphatic Capillaries

All lymph eventually returns to one of two ducts in the upper center part of your chest. The thoracic duct originates in your abdomen, where it collects lymph from your legs, your intestine, and your other internal organs. As it proceeds upward into your chest, the thoracic duct collects lymph from your thoracic organs, your left arm, and the left side of your head and neck.

The right lymphatic duct collects lymph from the right side of your chest wall, your right arm, and the right side of your head and neck. Both lymphatic ducts reenter your bloodstream where the large veins from your head and arms - the right and left jugular veins and subclavian veins - join in your upper chest.

Lymphatic Ducts

Lymph Composition

Lymph contains a variety of substances, including proteins, salts, glucose, fats, water, and white blood cells. Unlike your blood, lymph does not normally contain any red blood cells.

The composition of lymph varies a great deal, depending on where in your body it originated. In the lymphatic vessels of your arms and legs, lymph is clear and transparent, and its chemical composition is similar to blood plasma (the liquid portion of blood). However, lymph contains less protein than plasma.

The lymph returning from your intestines is milky, owing to the presence of fatty acids absorbed from your diet. This mixture of fats and lymph is called chyle, and the special lymphatic vessels surrounding your intestine that collect chyle are called lacteals. Lacteals drain into a dilated sac - the cisterna chyli (meaning 'reservoir for chyle') - at the lower end of the thoracic duct. The thoracic duct then conveys the chyle to your bloodstream, where the fats it carries can be processed for energy or storage.

Lymphatic Ducts

As lymph flows through your lymphatic vessels, it passes through lymph nodes. There are about 600 of these small, bean-shaped organs scattered strategically throughout your body. In the lymph nodes, lymph is filtered for bacteria, cancer cells, and other potentially-threatening agents.

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