Anatomy of the lymph vessels
The lymph vessels are anatomical structures that run through the entire body like blood vessels. Just like blood vessels, lymph vessels also transport a fluid. As the name already suggests, the lymphatic fluid is transported through the lymph vessels.
The anatomy of the lymph vessels is very similar to the anatomy of the blood vessels, with the difference that lymph nodes are always interposed between the individual lymph channels. In order to understand the anatomy of the lymph vessels, one must first understand their function. The lymph vessels transport tissue fluid (lymph) together with the proteins and white blood cells (lymphocytes) contained in it from the periphery of the body towards the center.
Roughly speaking, the periphery refers to everything that is further away from the heart (legs and arms, i.e. the extremities). From there, the fluid is transported via the lymph vessels and flows into the vein angle in the area of the heart (confluence of the internal jugular vein and the subclavian vein to the brachiocephalic vein). The anatomy of the lymphatic vessels is very similar to that of the veins, except for one crucial difference.
While the blood flow of arteries and veins is always connected and not interrupted, the lymphatic system has so-called blind ends. This means that the lymphatic vessels begin blind with one end open in the tissue, similar to a straw that is open on one side. These lymphatic vessels, which begin blind in the periphery, are called lymph capillaries or initial lymphatic vessels.
These are extremely narrow vessels that are located in the intercellular spaces and from there can absorb the tissue fluid. The anatomy of the lymph vessels thus begins with a special feature. In the blood system there are also capillaries, but they are connected to each other.
The lymphatic vessels, on the other hand, are open in the tissue and can therefore absorb the fluid from the intercellular spaces. Small anchor filaments are attached to the lymph vessels, which ensure that the vessel cannot slip. In addition, these filaments ensure that the inside (lumen) of the lymph vessels remains open and that the fluid can flow in.
The anatomical structure of the lymph vessels following the lymph capillaries are the so-called precollaterals. These arise when several of the 50μm wide lymph capillaries unite to form a lymph vessel that is approximately 100μm wide. This represents a confluence of several lymph capillaries and transports the fluid towards the left breast with the help of muscle cells.
In addition to the transport function, the pre-collaterals also serve to absorb further lymph fluid from the surrounding tissue. The anatomy of the lymph vessels is therefore quite simple. Next, several precollaterals unite to form a larger collector lymph vessel (or collateral lymph vessel).
In comparison to capillaries and precollaterals, collaterals serve exclusively to transport the lymph fluid. No further fluid is absorbed from the tissue. These collaterals each have a diameter of 150 to 600 μm.
The anatomy of these lymph vessels is almost identical to that of the veins. The collaterals have the histological classic three-layer wall structure (intima, media and external) and have additional valves which ensure that the fluid is transported in the direction of the left breast and does not sink into the arms or legs. The area between two valves is called lymphangion in lymphatic vessels.
This area contracts 10-12 times per minute and thus ensures that the lymph is transported further. A total of 3 subforms of the collaterals can be distinguished. The anatomy of the lymph vessels additionally ensures that these three systems are connected to each other.
This allows the lymph to flow from the deep system into the superficial system. The connection between the vessels is called anastomosis or perforation circulation.
- The superficial (epifascial) system lies in the subcutaneous fatty tissue and absorbs lymph from the skin and fatty tissue.
- The deep (subfascial) system, which is found in the arms and legs (extremities) and trunk, absorbs lymph from muscles, ligaments, joints and bones.
- Finally, there is the visceral system, which receives lymph from the various organs.
A special feature of the anatomy of the lymphatic vessels are the lymph collection points.
These are the largest lymph vessels in the human body. Depending on their location, they are divided into the upper or lower half of the body.Among them are the tracheal trunk (Truncus trachealis) and the thoracic duct (Ductus thoracicus), which is about 40 cm long. These collection points take up lymph from the collaterals.
They then flow into the left vein angle in the area of the heart. At this point, the anatomy of the lymph vessels connects with the anatomy of the venous system. The structure of the lymph vessels is generally very similar to the structure of the veins, especially in the larger lymph vessels (collaterals).
Similar to the veins, the lymph vessels also have a three-layer wall structure, which classically consists of an intima, a media and an external. The valves of the lymphatic vessels are another similarity. As with the veins, the valves of the lymph vessels are intended to ensure that the fluid (lymph) can be transported from the periphery, for example from the leg, towards the left breast.
Since the fluid must flow in the opposite direction to gravity, the lymph vessels need valves to ensure adequate flow and prevent backflow. These valves are only found in larger lymph vessels such as the collaterals, not in the capillaries and pre-collaterals. In contrast to the venous system, the valves of the lymph vessels are passive.
They are present in the larger lymph vessels at a certain distance and depending on their diameter. If there is a reduced function of the valves of the lymphatic vessels, it is possible that the fluid can no longer be adequately transported and the formation of so-called lymphedema can occur. In general, a malfunction of the valves of the lymph vessels is rather rare compared to a reduced venous valve function.
All articles in this series:
