Lymphatic System (a1605)

LYMPHATIC SYSTEM (GLANDS, VESSELS), a system of clefts, channels, vessels, and special formations (lymphatic glands) along their course, which drain the so-called lymph (see) from tissues. The concept of the lymphatic system also includes certain formations of adenoid tissue (see). These include 1) individual lymphatic follicles (noduli lymphatici solitarii) and their conglomerates (noduli lymphatici aggregati), located in the walls of the digestive tract and in the respiratory tract, 2) the thymus gland (glandula thymus), 3) the spleen, and 4) the bone marrow. The serous cavities of the body also belong to the lymphatic system: the abdominal, pleural, pericardial, and (in men) the cavity of the tunica vaginalis of the testes. (Regarding lymph circulation, see Lymph.) Phylogenesis of the lymphatic system. As a system separate from the circulatory system, the lymphatic system is inherent to all vertebrates, starting with fish. However, in most bony fish, it is not possible to identify lymphatic vessels in an injected state using the usual research methods by which these vessels can be easily detected in other vertebrate animals standing at a higher stage of development. Usually, with this injection, only the veins are filled with the injection fluid. To clarify the gradual development of lymphatic vessels, i.e., the replacement of lymphatic clefts with lymphatic tubes as the vertebrate organism develops from a lower form to a higher one, it is advisable to provide a brief description of the lymphatic system of some vertebrate animals by individual classes. The lymphatic system of frogs consists of extensive subcutaneous spaces formed by the skin and adjacent organs covered by fasciae, and of extensive chyle sacs formed by two layers of mesentery. Lymphatic vessels, easily identified by the puncture method under the serous membrane of the digestive tract, empty into the chyle sacs. Since the lymphatic vessels of the digestive tract are a continuation of the clefts of the chyle sacs along the course of the blood vessels, the vessels identified under the serous membrane of the digestive tract represent the same perivascular clefts as the lymphatic pathways between the layers of the mesentery. By puncturing the muscles and skin, it was not possible (Iosifov) to identify the lymphatic vessels of the trunk and limbs, although the organs are abundantly impregnated with a colorless fluid, lymph. From the subcutaneous lymphatic spaces and chyle sinuses, lymph is pumped by the anterior and posterior lymphatic hearts. Two anterior hearts are located near the spine; they are covered by the shoulder blades. The posterior hearts consist of several vesicles and are located in the pelvic region, near the coccyx. In a living frog, after an incision of the skin in the depression between the pelvis and the coccyx, one can see how the posterior heart pulsates, which pumps the transparent fluid—lymph—into the pelvic vein (figures 1, 2, and 3). The same can be observed from the side of both the anterior and posterior lymphatic hearts in tadpoles after removing the skin.

Figure 1. Lymphatic system of a frog (on the left side, the lymphatic hearts are dissected; on the right, they are covered by fasciae): 1—v. jugul.; 2—brachial plexus of nerves and subclavian artery; 3—left anterior heart and its connection with v. vertebr., emptying into v. jugularis; 5 and 6—posterior heart, consisting of two vesicles connected to the femoral vein (4); 7—septum between the subcutaneous lymphatic spaces of the back and thigh; 8—right anterior heart visible under the raised edge of the shoulder blade.

FIG. 2.

Figure 3. Lymphatic system of mammals. The lymphatic system is most developed in mammals. The main lymphatic vessels can be divided into Figure 2. Anterior lymphatic heart of a frog, opened: on the outlet opening into the vein, two semilunar valves are visible; the inlet openings are marked by hairs inserted into them. Fig. 3. Left anterior lymphatic heart of a frog, lying on the transverse process of the third cervical vertebra, with three inlet openings and a vein into which the heart pours lymph; the inlet openings are marked by hairs inserted into them (enlarged). subcutaneous and deep. These vessels are easily identified by the tissue puncture method, with the exception of the lymphatic vessels of the spleen, brain, and placenta. In the remaining areas of the body of mammals and humans, the lymphatic system consists of tubes running parallel to blood vessels and interrupted at certain places by lymph nodes. By location, lymphatic vessels can be divided into subcutaneous and deep, main and secondary trunks, and capillary networks. The main subcutaneous trunks collect lymph via secondary trunks from the capillary networks of the skin and subcutaneous tissue and pass in the subcutaneous fat layer parallel to the main subcutaneous veins and nerves. They are easily identified by puncture into the skin and subcutaneous fatty tissue. The main deep Figure 4. Deep lymphatic vessels of the hind limb of a dog, injected with India ink through a puncture into the muscles: 1—lgl. ilio-femorales; 2—muscular branch of a. tibialis post. and the two accompanying lymphatic trunks emerging from m. gastrocnemius; 3—a. tibialis post. with two accompanying lymphatic vessels; 4—a. femor. caudalis and the accompanying lymphatic vessel originating from the muscles nourished by this artery; 5—a. femoralis and the accompanying outer and inner groups of lymphatic vessels; 6—a. epigastrica caudalis and the accompanying lymphatic vessel, injected through a puncture into the thickness of the abdominal muscles; 7—a. iliaca ext. with a plexus of deep lymphatic vessels bringing lymph from all organs of the limb to three lymph glands—lgl. ilio-femorales; 8—aorta abdominalis; S—m. sartorius; F—m. transversus abd.; R—ram. semimembranosus et adductor. deep trunks pass together with the main deep blood vessels and nerves and collect lymph from organs with the help of secondary trunks, which originate in the capillaries of organs located under the fascia (Figure 4). The trunks are equipped with valves and therefore have a beaded appearance. In the walls of the vessels and nodes, there is musculature, by the contraction of which lymph is set in motion and moves toward the outlet into the veins. In addition, an auxiliary force for the movement of lymph is the suction effect of the respiratory

movements of the chest, the pulsation of arteries, and muscle contractions. The influence of the contraction of the diaphragm on the initial expanded part of the thoracic duct (cisterna chyli) is so great that in both mammals and humans, this cistern can be considered a passive lymphatic heart (Figs. 5 and 6). The rhythmic action of the musculature located in the walls of the vessels in the segments between the valves is similar to the rhythmic action of the active lymphatic hearts of lower animals; therefore

Figure 5.

Figure 6. Figure 5. Formation of the thoracic duct and its cistern (dilation) in a dog: 1—aorta; 2—v. azygos; 3—d. thorac.; 4—trunci intestinalis; 5—cisterna chyli; 6—tr. lumbalis. Figure 6. Formation of the thoracic duct and its cistern (dilation) in a human: 1—d. thorac.; 2—cisterna chyli at the initial end of the thoracic duct, formed by the fusion of the right and left lumbar trunks; 3—intestinal trunk; 4 and 5—lumbar glands. Ranvier considers each segment of lymphatic vessels between the valves to be a separate lymphatic heart. The lymphatic system of frogs, lizards, and eels (Fig. 7) represents, in comparison with the lymphatic system of birds (Fig. 8) and Fig. 7. Lymphatic system of an eel; 1—hair inserted through the cavity of the head sinus into the opening leading to the jugular vein; 2—hair inserted through the cavity of the head sinus into the opening through which the paravertebral trunk opens into the head sinus; 3—valve at the inlet opening of the head sinus; 4—right paravertebral lymphatic trunk; 5—jugular vein; 6—anastomosis of the paravertebral lymphatic trunks; 7—aorta; 8—chyle ducts; 9—kidney; 10—main intestinal sinus; 11—sinus of the genital organ; 12—genital organ; 13 and 14—caudal artery and vein; 15—continuation of the vertebral lymphatic trunks in the tail; 16—longitudinal intestinal sinus; 17—subserous lymphatic network of the stomach; 18—liver sinus; 19—head lymphatic sinus. mammals, a lower form of development and consists of extensive lymphatic cavities from which lymph is pumped by active and passive hearts. The chyle sacs receive lymph from the wall of the digestive tract through channels representing peri

Figure 8. Lymphatic system of a pigeon: 1—lymphatic vessels accompanying the jugular vein with two trunks in the neck region; 2—lymphatic vessels of the forearm; 3—emptying of the lymphatic vessels of the forelimb into the angle of the fusion of the jugular and subclavian veins; 4—lymphatic vessels of the shoulder; 5—thoracic duct; 6—lymphatic vessels accompanying the abdominal aorta; 7—lymphatic vessels in the kidney region; 8—lymphatic vessels of the small intestine; 9—lymphatic vessels of the stomach; 10—lymphatic vessels accompanying the caudal vein; 12—lymphatic vessels of the hind limb in the lower leg region accompanying blood vessels with two trunks; 13—lymphatic vessels of the thigh.

vascular spaces. Similar perivascular spaces are revealed by injection by the method of pricking into the thickness of the trunk muscles of eels, whereas in frogs and lizards they are absent, and it must be assumed that in the latter animals there are no preformed lymphatic capillaries and perivascular spaces in the area of the trunk and limbs; instead of them (capillaries and perivascular spaces) among the muscular tissue there exist simple lymphatic clefts. The existence of extensive lymphatic clefts in the aforementioned lower vertebrates fully corresponds to the function of these clefts as exclusively collectors of lymph, which is pumped into the blood by lymphatic hearts. In higher animals, the lymphatic clefts are replaced by tubes equipped with valves and muscles, serving to move lymph into the blood. Consequently, in higher vertebrates, lymphatic tubes serve not only as collectors but also as apparatuses for moving lymph. The gradual development of the L. s. corresponding to the complication of its function is indicated by the absence of lymphatic nodes (glands) in frogs, lizards, eels, and non-swimming birds. Lymphatic nodes first appear in a relatively small number compared to mammals in swimming birds (Fig. 9). In animals in which lymphatic glands are absent, the function of the latter is performed by adenoid organs (follicles) of the digestive tract, the thyroid gland, and bone marrow. Bartels, who studied the ontogenesis of the L. s., found that in pig embryos 67 cm long, the subcutaneous lymphatic vessels are already fully developed. Regarding the earlier stage of development of lymphatic vessels, Bartels says the following: "The development of lymphatic vessels and the thoracic duct is at least in the first stages even darker than the development of blood vessels. Indeed, some authors imagine that in the mesenchyme clefts form, which merge and the edges of which are covered with a sheath of endothelial cells, formed from the transformation of neighboring cellular elements into endothelium. But voices are also heard, which speak in favor of the development of lymphatic so

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