Lymphatic Capillaries

What are lymphatic capillaries?

Lymphatic capillaries (CAP-uh-lair-eez), also called lymph capillaries, are tiny vessels that exist throughout your body. A capillary is a tiny tube with an inside diameter as thin as a hair.

Lymphatic capillaries are similar to blood capillaries, but they are larger in diameter and have closed ends. Unlike blood capillaries, fluid can flow into lymph capillaries but can’t flow out through the cell walls. It can only move forward.

Lymphatic capillaries belong to your lymphatic 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?

Lymph capillaries help keep the overall fluid balance in your body. Throughout your body, interstitial fluid (fluid found in the spaces around cells) leaks from blood capillaries into your tissues. Lymph capillaries pick up this fluid and help return it to your circulatory system.

What is lymph?

Lymph, also called lymphatic fluid, is the extra interstitial fluid that drains from your body’s cells and tissues. The fluid is watery and colorless.

Lymph includes substances such as:

• Cancer cells.
• Damaged cells.
• Fats.
• Foreign invaders, including bacteria and viruses.
• Minerals.
• Nutrients.
• Proteins.
• White blood cells (lymphocytes) that fight infections.

How do lymphatic capillaries function?

Lymph capillaries have walls that only work one way, to let fluid in. As lymph capillaries collect interstitial fluid from tissues, the pressure in the lymph capillaries grows. This increasing pressure moves the lymph fluid forward toward the heart.

Everywhere in your body, your lymphatic capillaries collect lymph and move it into larger lymphatic vessels. Along the way, the lymph 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. Lymph 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 keep the fluid moving one way.
3. The collecting ducts empty the lymph into the right or left lymphatic duct (thoracic duct). The right lymphatic duct, near the base of your neck, collects lymph from the right side of your arm, chest and neck. The thoracic duct starts near the bottom of your spine. It collects lymph from your abdomen, lower chest and pelvis.
4. The lymphatic ducts empty the lymph into your subclavian veins. These veins, located below your collarbone, join to form the superior vena cava. The vena cava returns clean lymphatic fluid to your bloodstream.

Returning this lymph to your bloodstream helps to:

• Maintain normal blood pressure and volume.
• Prevent fluid from building up around tissues (edema).

What is the structure of lymphatic capillaries?

Lymphatic 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 closed at one end. They contain a mini-valve that lets interstitial fluid flow into but not out of them.

Lymphatic capillaries consist 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 elastic fibers and attach the endothelial cells to fibroblast cells in connective tissue.

Where are the 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 your:

• Avascular tissues, meaning body tissue without blood vessels. Avascular tissues include cartilage, the cornea and lens of your eye and the epithelial (outermost) layer of your skin.
• The central nervous system, including your brain and spinal cord.

What conditions affect the lymphatic capillaries?

Conditions that affect the lymphatic capillaries include:

• Adult Hodgkin’s lymphoma and adult non-Hodgkin’s lymphoma: These two types of cancer develop in the lymph 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 blockage results in swelling of various body parts, usually in your arms, legs or genitals. Mosquito bites that carry parasitic worms cause elephantiasis.
• Lymphangitis: Wounds or cuts infected due to viruses or bacteria lead to inflammation of the lymphatic vessels.
• Lymphedema: Excess lymph collects in your body’s soft tissues, usually the arms or legs, and causes swelling. Lymphedema can be genetic or caused by disease or damage to your lymph nodes, often by cancer treatment, surgery or recurrent infection to the limbs, such as cellulitis.

How do I care for my lymphatic capillaries?

You can take care of your capillaries by:

• Drinking water and staying hydrated so that lymph can move easily through your body.
• Limiting exposure to toxic chemicals (as in cleaning products or pesticides). A buildup of chemicals can make it harder for your body to filter waste.
• Living an active lifestyle.
• Maintaining a healthy weight.
• Visiting your doctor immediately if you suspect a cut has become infected.

When should I call a doctor 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 healthcare 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.

A note from Cleveland Clinic

Lymphatic capillaries are tiny vessels found in the tissues of most organs in your body. They transport and filter lymphatic fluid (lymph) from your body’s cells and tissues. Lymph capillaries help to keep consistent blood pressure and volume and prevent fluid buildup. Though several conditions can affect lymphatic capillaries, you can reduce your risk by living a healthy lifestyle and seeing your doctor regularly. Lymphedema is a chronic condition that most often requires non-surgical management.