Human Anatomy, Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovsky 2008

Special Part
Lymphatic System (systema lymphaticum [systema lymphoideum]) – General Overview
Components of the Lymphatic System – Lymphatic Capillaries

The Lymphatic system consists of the following vascular links:

1. Lymphocapillary vessels, vasa lymphocapillaria.

2. Lymphatic postcapillaries, vasa postlymphocapillaria.

3. Lymphatic vessels, vasa lymphatica.

4. Lymphatic trunks, trunci lymphatici.

5. Lymphatic ducts, ducti lymphatici.

The lymphatic ducts empty into the right and left venous angles (Pirogov's angle), which are formed by the internal jugular and subclavian Veins. As noted earlier, Lymph Nodes are located along the course of the lymphatic vessels. The segments of the lymphatic system can serve pathways for the spread of malignant tumor Cells (metastases), a factor that must be considered during surgical interventions.

Lymphatic capillaries, vasa lymphocapillaria, represent the primary link, or roots, of the lymphatic system. They form a network of thin endothelial tubules whose walls consist of a single layer of squamous endothelium (Fig. 101 A). Using light Cell/15.html">Microscopy, O. O. Sushko and L. V. Chernyshenko (1966) established that lymphatic capillaries are composed of stellate and polygonal endothelial cells. The diameter of lymphatic capillaries ranges from 50-200 µm, which is several times greater than that of Blood capillaries (8-10 µm). Lymphatic capillaries permeate nearly all human Tissues and Organs, with the exception of the Brain, splenic parenchyma, epithelial covering of the Skin, cartilages, Cytology/practical/76.html">Cornea of the Eyeball, lens, Placenta, and umbilical cord.

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Fig. 102. Two-layer network of lymphatic capillaries and vessels in the skin of the epigastric region of a newborn. Oc - 8; Obj - 4. (Prepared by O. I. Svyrydov)

Lymphatic capillaries begin as loops, blind finger-like outgrowths with irregular contours, or closed lymphocapillary networks located in one or multiple planes. Lymphatic capillaries are characterized by the following features: marked tortuosity, numerous dilations alternating with sudden constrictions, and the presence of lacunae at their confluence sites. Lymphatic capillaries anastomose with one another to form closed lymphocapillary networks, which can be single-, double-, or multi-layered (Fig. 102). The architectonics of lymphatic capillary networks is characteristic of each individual organ, depending on their Structural and functional Organization as well as the branching patterns of their fibrous structures (D. A. Zhdanov, O. O. Sushko, L. V. Chernyshenko, O. I. Svyrydov). Thus, in tubular organs (such as the intestine) or lamellar structures (such as organ capsules and fascia), lymphatic capillaries form flat networks, whereas in parenchymal organs (such as the Kidneys, Liver, and Lungs), they form three-dimensional networks.

Lymphatic capillaries differ from blood capillaries in the following main features:

- absence of a basement membrane;

- blind-ending terminals;

- absence of pericytes;

- presence of anchoring filaments that fix the endothelial cells;

- larger diameter compared to blood capillaries;

- greater permeability to substances present in the tissue fluid compared to the endothelium of blood capillaries.

Fig. 103. Diagram of The Structure of a lymph node (based on A. Maximow, with modifications)

Lymphatic capillaries perform the following Functions:

1. They resorb colloidal solutions from tissues that have not been absorbed by blood capillaries.

2. Together with veins, they ensure tissue drainage (absorption of Water and dissolved crystalloids).

3. Under pathological conditions, they remove foreign particles and microbes from tissues.

Lymphatic capillaries transition into postcapillaries. The latter are structurally similar to

to the capillaries, but differ from them in having Valves whose wall is formed exclusively by the endothelium (V. V. Kuprianov (1969), L. V. Chernyshenko (1983), Yu. I. Borodin, M. R. Sapin, L. E. Etingen et al., (1990)). Lymphatic postcapillaries regulate lymph flow in organs and transition into intraorgan lymphatic vessels.