Lymphatic Capillaries

What are lymphatic capillaries?

Lymphatic capillaries, also called lymph capillaries, are tiny vessels throughout your body. They move lymphatic fluid (lymph) around and help keep it from building up. A capillary is a tiny tube with space inside as thin as a hair.

A lymphatic capillary is similar to a blood capillary. But lymphatic capillaries are larger in diameter (around) and have closed ends. Unlike with blood capillaries, fluid can flow into lymph capillaries but can’t flow out through the cell walls.

Lymphatic capillaries belong to your lymphatic system, which is part of your immune system. Your lymphatic system includes vessels, tissues and organs to collect extra fluid from nearly every organ in your body.

What do lymphatic capillaries do?

The function of your lymph capillaries is to help maintain your body’s overall fluid balance. All around your body, interstitial fluid (fluid found in the spaces around cells) leaks from blood capillaries into your tissues. Lymphatic capillaries pick up this extra interstitial fluid (lymph) that drains from your body’s cells and tissues.

Lymphatic capillaries help return lymph to your circulatory system. By returning this lymph to your bloodstream, lymphatic capillaries help maintain normal blood pressure and volume. They also help prevent fluid from building up around tissues (edema).

How do they work?

Lymph capillaries have permeable (pass-through) walls that only work one way — to let fluid in. Pressure inside these capillaries grows as they collect interstitial fluid from tissues. This increasing pressure moves the lymph fluid forward toward your heart.

Throughout your body, your lymphatic capillaries collect lymph and move it into larger lymphatic vessels. Along the way, the lymph fluid passes through lymph nodes, which filter and clean the lymph. Eventually, your body discards the waste and returns the filtered lymph to your bloodstream to begin the cycle again.

Here’s how the rest of the cycle works:

1. Lymphatic capillaries send lymph into larger tubes called lymphatic vessels.
2. The lymphatic vessels come together in still-larger tubes called collecting ducts. A series of valves keeps the fluid moving one way.
3. The collecting ducts empty the lymph into the right or left lymphatic duct (thoracic duct).
4. The lymphatic ducts empty the lymph into your subclavian veins. These veins join to form the superior vena cava. The vena cava returns clean lymphatic fluid to your bloodstream.

Where are lymphatic capillaries located?

Lymph capillaries are found between cells (in the interstitial space). These capillaries are in the tissues of every organ in your body, except for bone marrow and your body tissues without blood vessels. These include cartilage and the epithelial (outermost) layer of your skin.

What are the parts of lymphatic capillaries?

A lymphatic capillary consists of:

• Endothelial cells, which line the capillary walls
• Basement membrane, which supports the endothelial cells
• Mini-valves, which let lymph flow into the capillaries but not out of them
• Anchoring filaments, which contain stretchy fibers and attach the endothelial cells to cells in connective tissue

What do they look like?

Lymphatic capillaries are tubes that are about 50 micrometers around (like a human hair). One end of the tube is closed and has an oak leaf shape. Lymph capillaries have thin walls, only as thick as a single cell. The cells overlap each other so that interstitial fluid easily enters the capillaries.

Lymphatic capillaries are similar to veins in that lymph moves in one direction, like blood in veins. Also, they both have thin walls.

What common conditions and disorders affect lymphatic capillaries?

Conditions that affect the lymphatic capillaries include:

• Adult Hodgkin lymphoma and adult non-Hodgkin lymphoma. These two types of cancer develop in the lymphatic system. They begin in white blood cells called lymphocytes.
• Edema. Interstitial fluid builds up in tissues faster than your body can remove it, causing swelling.
• Elephantiasis (lymphatic filariasis). A blockage of your lymphatic system leads to a backup of lymphatic fluid. This causes swelling of various body parts, usually in your arms, legs or genitals.
• Lymphangitis. Wounds or cuts infected with viruses or bacteria lead to inflammation of your lymphatic vessels.
• Lymphedema. Excess lymph collects in your body’s soft tissues, usually your arms or legs, and causes swelling. This is a chronic condition that most often requires nonsurgical management.

Common signs or symptoms of lymphatic capillary conditions

Symptoms of conditions that affect lymphatic capillaries may include:

• Fatigue
• Fever
• Chills
• Belly pain
• Swollen lymph nodes
• Unexplained weight loss
• Difficulty walking or breathing
• Swelling

Common tests to check the health of lymphatic capillaries

Tests for checking your lymph capillaries’ health may include:

• Blood tests
• CT (computed tomography) scan
• MRI (magnetic resonance imaging)
• PET (positron emission tomography) scan
• Doppler ultrasound
• Skin biopsy

What are common treatments for lymphatic capillary issues?

Treatments may include:

• Medicine
• Compression therapy
• Lymphatic drainage massage
• Chemotherapy
• Immunotherapy
• Radiation therapy
• Surgery

How do I care for my lymphatic capillaries?

You can take care of your lymphatic capillaries in these ways:

• Drink water and stay hydrated so that lymph can move easily through your body.
• Limit your exposure to pesticides, cleaners or other products that could harm your body.
• Get 150 minutes of physical activity every week.
• Maintain a weight that’s healthy for you.
• Visit your healthcare provider immediately if you suspect you have an infected cut.

When should I call a healthcare provider about my lymphatic capillaries?

It’s important to stay current with preventive care, including annual physical exams. That way, your healthcare provider can detect problems at an early stage.

Contact your provider if you experience symptoms including:

• Cuts or wounds that don’t heal quickly
• Extreme fatigue that lasts for more than a few weeks
• Unexplained swelling that lasts for more than a few weeks or impacts your daily activities