Wall structural features
The wall of the lymphatic capillary is extremely simplified to ensure maximum permeability. Unlike blood capillaries, there are no pericytes and no basement membrane. The entire structure is formed exclusively by a single layer of cells — endothelium.
Lymphatic capillary endothelial cells have a number of unique morphological features:
- Size: The cells are significantly larger than their counterparts in blood capillaries.
- Surface: Numerous microvilli are located on the basal side facing the interstitium (surrounding tissue).
- Cytoplasm: Contains a vast number of pinocytotic vesicles and lysosomes. The function of lysosomes here is critically important — they break down ballast components entering with the tissue fluid.
- Contacts: Intercellular contacts between adjacent endothelial cells are very weak, which is the main condition for high wall permeability.
Anchoring (stay) filaments
Due to the absence of a distinct basement membrane and strong intercellular contacts, the capillary requires an external supporting framework. This supportive function is performed by anchoring (fixing) filaments — specialized structures characteristic exclusively of lymphatic capillaries.
Their main task is to provide reliable mechanical connection between the vessel and the surrounding interstitium. The mechanism of their topographical attachment is as follows:
- Proximal end: attached to the outer surface of endothelial cells. Most often, this occurs in the zones of intercellular contacts.
- Distal end: firmly interwoven into bundles of collagen fibers of the connective tissue running parallel to the capillary axis.
When visualized using electron microscopy, these filaments appear as thin fibrous structures extending from the basal surface of the endothelial cell into the surrounding tissue.
Tissue fluid drainage physiology
Anchoring filaments are not just a static support. They play a key role in ensuring drainage function, i.e., the entry of interstitial fluid into the lumen of the lymphatic capillary. The mechanism of their action directly depends on the volume of fluid in the tissues.
Mechanism of "sluice" opening:
- Fluid accumulation: During tissue edema, the volume of tissue fluid increases. This creates intense mechanical pressure on the surrounding matrix.
- Tension: Under pressure, collagen fibers shift. This displacement causes tension in the anchoring filaments connected to them.
- Opening: Strongly stretched filaments mechanically pull the endothelial cell wall, literally "pulling apart" the weakly connected cells.
- Result: Intercellular clefts form or significantly expand between endothelial cells. Through these open spaces, fluid flows freely from the interstitium into the lumen of the lymphatic capillary.
Briefly: answers to topical questions
What specific proteins do anchoring (stay) filaments consist of?
Anchoring filaments are collagenous in nature. The exact protein composition (specific types of collagen or other proteins) is not specified in these materials.
In which human organs and tissues are lymphatic capillaries completely absent?
Lymphatic vessels and capillaries are absent in the following tissues and organs:
- Epithelium
- Cartilage tissue
- Brain
- Red bone marrow
- Eyeball
- Placenta
What embryonic source serves as the precursor for the endothelium of lymphatic capillaries?
The embryonic source of lymphatic capillary endothelium is not specified in these materials.
Imagine a tent with guy lines. The tent fabric is the endothelium, and the ropes are the anchoring filaments. When it rains (tissue edema), the ground swells, the pegs (collagen fibers) shift and pull the ropes. As a result, the tent entrances (intercellular clefts) open slightly, letting water through.
Class and exam questions
What is the main difference between the wall of a lymphatic capillary and a blood capillary?
Pericytes and the basement membrane are completely absent in the lymphatic capillary, and intercellular contacts between endothelial cells are very weak.
Why are there so many lysosomes in the cytoplasm of lymphatic capillary endothelial cells?
The abundance of lysosomes is necessary for the efficient destruction of ballast components entering the cell from the tissue fluid.
Which tissue structures do anchoring filaments bind to?
The distal ends of anchoring filaments intertwine into bundles of connective tissue collagen fibers running parallel to the capillary.
What else to study on this topic
- Endothelial ultrastructure: electron microscopy
- Organization of endothelial intercellular contacts
- Pinocytotic activity of the capillary wall
- Interaction of capillaries with collagen fibers
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