Human Anatomy (with the Fundamentals of Dynamic and Sports Morphology) - Ivanitsky, M. F. 2008

The Doctrine of the Heart and Blood Vessels
The Lymphatic System and Organs of Immunogenesis

The Lymphatic system

The lymphatic system forms a vascular network. It is closed at the periphery and drains centrally into the large Veins OF THE neck. Its structural components include lymphatic capillaries, Lymphatic vessels, lymphatic trunks, lymphatic ducts, and Lymph Nodes. All of these are filled with a fluid known as lymph.

The Functions of the lymphatic system are diverse: cleansing, drainage, barrier, immune defense, storage (depot), and Lymph formation. Lymphatic capillaries cleanse Tissues of metabolic products that cannot penetrate Blood capillaries (high-molecular-weight Proteins, foreign particles, etc.). These substances are transported with the lymph flow into lymphatic vessels, each of which is interrupted by at least one lymph node, where certain substances are retained. The nodes serve as sites for The production of lymphocytes and protective proteins (Antibodies) that provide Immunity.

Lymphatic capillaries. The diameter of lymphatic capillaries is larger than that of blood capillaries and varies significantly (10–200 µm). Functioning as auxiliary pathways (alongside Blood Vessels) for tissue cleansing, lymphatic capillaries are not present everywhere. They are absent from the Brain, splenic parenchyma, epithelium of the Skin and mucous membranes, Cartilage, sclera and lens of the eye, Placenta, Liver lobules, the Endocrine portion of the Pancreas, and renal corpuscles.

Unlike blood capillaries, lymphatic capillaries lack a basement membrane and associated pericytes; they retain only a single layer of endothelial Cells. These cells form extensions—microvilli—that project not only into the capillary lumen but also outward into the surrounding Connective Tissue ground substance. Endothelial cells exhibit varied shapes, a poorly developed Endoplasmic reticulum, and an Abundance of micropinocytic vesicles designed to transport substances absorbed from surrounding tissues across the Cytoplasm into the vessel lumen. Gaps between endothelial cells, measuring up to 12 µm in width, alongside The process of pinocytosis, enable lymphatic capillaries to absorb particles from surrounding tissues. Collapse of the lymphatic capillaries is prevented by closely associated connective tissue fibers that act as stay cables (similar to parachute suspension lines).

Lymphatic vessels. Unlike lymphatic capillaries, these vessels feature endothelial projections—Valves—that regulate lymph flow. They are characterized by longitudinal undulating contours, and larger vessels acquire a beaded appearance when stretched.

Lymphatic vessels are subdivided into superficial and deep. Based on their wall Structure, they are classified into muscular vessels (the majority) and those lacking smooth Muscle elements. The latter are simply endothelial tubes covered with connective tissue. Muscular-type lymphatic vessels contain approximately the same amount of smooth muscle fibers as Arteries of a similar diameter, and significantly more than veins. The Development of the muscular layer is determined by the vessel's Location and the Specific characteristics of lymph flow within it. In the superficial Vessels of the arm and forearm, this layer is less pronounced than in the corresponding vessels of the thigh and leg.

Lymph propulsion is facilitated by anastomoses between Lymphatic vessels and fluid storage mechanisms in the form of easily distensible vascular plexuses. Other factors driving lymph flow include the energy of lymph formation (driven by the continuous influx of fluid from body tissues into lymphatic capillaries), active contraction of smooth muscle elements in the walls of lymphatic vessels, skeletal Muscle contraction, displacement of Internal Organs, Heart movements, and the suction effect of the thoracic cavity.

Lymphatic trunks and ducts. These exceed lymphatic vessels in diameter and wall thickness. There are two main lymphatic ducts: the Thoracic duct and the Right lymphatic duct.

The thoracic duct (Fig. 101) is formed by the confluence of two lumbar trunks (left and right) at the level of the 12th thoracic and 1st lumbar vertebrae. It frequently originates from a dilation known as the cisterna chyli. Situated posterior and to the right of the aorta, the thoracic duct passes through the aortic hiatus into the thoracic cavity, entering the posterior Mediastinum. It then ascends to the right of the aorta and shifts to the left at the level of the 4th and 5th thoracic vertebrae. Reaching the level of the 7th cervical vertebra, it forms an arch and empties into the left venous angle—the junction of the left subclavian and left internal jugular veins. Before this point, three lymphatic trunks empty into the thoracic duct: the left bronchomediastinal, subclavian, and jugular trunks. Less frequently, these trunks open independently into the neck veins. The thoracic duct drains lymph from one-quarter of the body: its lower half, the left half of the HEAD, neck, and Thorax along with the internal organs located in this half, as well as the left upper extremity.

The right lymphatic duct is formed by the union of the right bronchomediastinal, subclavian, and jugular trunks and empties into the right venous angle, formed by the right subclavian and right internal jugular veins. Much more frequently than on the left side, these trunks drain independently into the neck veins. The right lymphatic duct receives lymph from one-quarter of The Human Body: the right half of the head, neck, and thorax, the organs located within this half, and the right upper extremity.

In the thoracic duct, the tunica interna contains longitudinally oriented bundles of muscle fibers, while the middle layer (tunica media) is particularly well-developed, consisting of spirally and longitudinally arranged fibers. The muscular component of the wall decreases from bottom to top (consequently, from the site where the thoracic duct passes through the Diaphragm to its opening, the wall becomes twice as thin). The rich innervation of their walls testifies to the intrinsic motor capabilities of lymphatic trunks and ducts. Effector Innervation of the thoracic duct is provided by postganglionic fibers (see The structure of the Autonomic Nervous system, p. 328) of Sympathetic trunk cells located in the external coat (adventitia) of the duct. The walls of lymphatic vessels, trunks, and ducts also contain vasa vasorum (vessels of vessels). It has been suggested that their activity along the pathways of lymph transport may increase lymph concentration due to Water reabsorption by blood capillaries.

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Fig. 101. The lymphatic system.

1 — deep parotid lymph nodes; 2 — superficial parotid lymph nodes; 3 — submandibular nodes; 4 — cervical nodes; 5 — thoracic duct; 6 — deep axillary nodes; 7 — deep cubital nodes; 8 — deep inguinal nodes; 9 — superficial inguinal nodes; 10 — superficial cubital nodes; 11 — superficial axillary nodes; 12 — subclavian nodes; 13 — occipital nodes; 14 — mesenteric nodes; 15 — cisterna chyli; 16 — iliac nodes; 17 — superficial lymphatic vessels of the leg (after B.N. Uskov)

Lymph nodes. These form more than 50 groups and are subdivided into somatic (body) nodes, visceral (internal organ) nodes, and mixed nodes (which receive lymph from both viscera and organs of locomotion). Lymph nodes are located along the course of blood vessels. In the upper extremity, these include axillary, humeral, and cubital nodes; in the lower extremity, inguinal, popliteal, anterior and posterior tibial, and fibular nodes. Visceral nodes are named after the organs they lie adjacent to and from which they receive lymph. For instance, in the Abdominal cavity, pancreatic, splenic, and hepatic nodes are distinguished, while in the pelvic cavity, perivesical, paracervical, paravaginal, and pararectal nodes are found, among others.

Because lymph drains from specific body regions through these defined groups of nodes, they are referred to as regional nodes.

Fig. 102. Pathways of lymph drainage from body regions:

1 — cubital nodes; 2 — axillary nodes; 3 — inguinal nodes; 4 — popliteal nodes; 5, 6 — lymph flow from the upper extremity; 7 — thoracic duct; 8 — intestinal trunk; 9 — lumbar trunk; 10, 11 — lymph drainage from the lower extremity

Knowledge of the course of lymphatic vessels toward regional nodes is essential for massage, all techniques of which must be performed taking into account the direction of venous BLOOD AND LYMPH flow (Fig. 102).

Head and Neck. Several groups of nodes are located in the head region: occipital, parotid (within the parotid gland bed), submental (between the anterior bellies of the digastric Muscles), and submandibular (in the submandibular triangle along with the Cytology/practical/98.html">Submandibular salivary gland).

In the neck region, lateral and anterior cervical nodes are distinguished.

Among the lateral nodes, there are those lying on the sternocleidomastoid muscle and deep nodes forming three chains along the Internal jugular vein, the Accessory nerve, and the transverse cervical artery. These nodes receive lymph from the skin, muscles, and BONES OF THE head and neck. Lymphatic vessels from the upper and lower Lips drain into the submental and submandibular lymph nodes, from which lymph is directed to the deep cervical nodes of the jugular chain. Lymph from the Teeth of the upper and lower jaws flows to the submandibular and upper deep cervical lymph nodes of the internal jugular chain, as well as to the retropharyngeal node. Lymphatic vessels of the Tongue lead to various regional nodes: from the tip of the tongue, they may pass through the submental nodes or the deep cervical nodes; from the body of the tongue, some vessels run to the submental nodes, while others lead to the deep cervical node of the jugular chain; from the ROOT of the tongue, they drain to the deep cervical nodes. Deep lymphatic vessels of the tongue pass through the submandibular lymph nodes, the deep cervical nodes of the jugular chain, and the retropharyngeal node.

Upper extremity. The regional lymph nodes of the arm are the cubital and axillary nodes. Deep cubital nodes are located deep within the cubital fossa, while one or two superficial nodes lie subcutaneously on the fascia, approximately 2 cm above the medial epicondyle of the humerus. The primary nodes are the axillary nodes, numbering 15–18 (sometimes 8–50) within the axillary fossa. These nodes are subdivided into lateral nodes (adjacent to the axillary artery and vein), subscapular nodes (located near the Origin of the vessels of the same name), central nodes (situated in the middle of the axillary inlet), pectoral nodes (lying on the serratus anterior muscle), and apical-axillary (subclavian) nodes.

The superficial lymphatic vessels of the upper limb originate from networks of lymphatic capillaries and plexuses of small vessels located in the skin and fascia of each digit. Gradually, these small lymphatic vessels converge into collecting vessels. The main superficial collecting vessels form three groups: medial (ulnar), lateral (radial), and a middle or palmar group.

The medial vessels arise from the skin of digits V, IV, and III of the hand, course along the posterior aspect of the forearm, shift to the anterior aspect, and drain into the superficial cubital nodes, from which lymph passes into the central axillary nodes.

The lymphatic vessels of the palmar group originate from the skin of the palm and the anterior aspect of the forearm; then, joining the vessels of the medial group, they course together toward the central axillary nodes.

The vessels of the lateral group originate in the skin of digits I and II and the lateral side of digit III, run along the lateral aspect of the forearm, pass onto the anterior surface of the arm, and head toward the central axillary nodes. One or two vessels join the cephalic vein and run alongside it in the lateral bicipital sulcus of the arm, subsequently reaching the upper axillary nodes via the deltopectoral groove.

The deep lymphatic vessels of the upper limb accompany the arteries and veins, are interrupted in the deep cubital node, and drain into the Lateral group of axillary nodes. Lymph from the mammary gland also drains into the axillary nodes. A significant portion of its lymphatic vessels empties into the pectoral lymph nodes lying on the serratus anterior muscle, while individual vessels pass to the lateral axillary, subscapular, and even the central axillary nodes.

There are transmural lymphatic vessels of the mammary gland which, piercing the pectoralis Major and minor muscles, head toward the apical axillary nodes or enter the thoracic cavity into nodes arranged in a chain along the sides of the internal thoracic artery.

Lower limb. The regional nodes of the lower limb are the popliteal nodes, located in the popliteal fossa, and the inguinal nodes, which lie beneath the inguinal ligament and are subdivided into superficial and deep. The lymphatic vessels heading toward these nodes are likewise divided into superficial and deep.

The superficial lymphatic vessels are subdivided into medial and posterolateral. The medial vessels course alongside Branches of the great saphena vein and collect lymph from the Medial surface of the dorsum of the FOOT, leg, thigh, and partly from the external genitalia, draining into the superficial inguinal nodes. The lymphatic vessels from the skin of the posterior thigh, gluteal region, and lower abdominal wall also empty into these nodes. The posterolateral lymphatic vessels accompany branches of the small saphenous vein. They drain lymph from the skin of the lateral margin of the foot, the calcaneal region, the PLANTAR ASPECT OF the foot, and the posterior leg. These lymphatic vessels empty into the popliteal nodes. The deep lymphatic vessels of the lower limb run alongside the Arteries of the foot, leg, and thigh into the deep inguinal lymph nodes. From the inguinal nodes, the efferent vessels ascend along the course of the external iliac artery.

Anastomoses exist not only between the superficial and deep lymphatic vessels along their course, but also between the superficial and deep lymph nodes.

Pelvic and trunk region. Lymphatic vessels from the walls and Organs of the pelvis pass through nodes located along the external iliac, internal iliac, and common iliac arteries. From these nodes, lymph reaches the lumbar lymphatic trunks. Lymph from the skin of the lower trunk (inferior to the umbilicus) drains via superficial lymphatic vessels into the superficial inguinal nodes. The deep lymphatic vessels of the abdominal cavity, which collect lymph from the walls and viscera, pass through nodes situated near the aorta and INFERIOR VENA CAVA. The number of these nodes ranges from 30 to 50. Vessels emerging from them drain into the lumbar trunks or the thoracic duct. The deep lymphatic vessels collecting lymph from the walls and organs of the thoracic cavity pass through intercostal nodes (anterior and posterior) and mediastinal nodes. The lymphatic vessels of the thoracic organs form two large trunks: the right and left bronchomediastinal trunks. The former empties into the right lymphatic duct, and the latter into the thoracic duct.

The lymph nodes of various organs and body parts exhibit local variations, but share a common structural plan (Fig. 103). Each node is enclosed in a connective tissue capsule that sends septa—trabeculae—into its interior. The parenchyma of the node forms a cortex, containing lymphoid follicles, and a medulla in the form of medullary cords. The capsule and trabeculae are separated from the node parenchyma by clefts known as sinuses. These include the marginal (subcapsular) sinus, intermediate (along the trabeculae) sinuses, and the hilar sinus (at the indentation On the surface of the node termed the hilum).

Fig. 103. Lymph node:

1 — capsule; 2 — hilum; 3 — capsular trabeculae; 4 — hilar trabeculae; 5 — marginal sinus; 6 — intermediate sinuses; 7 — hilar sinus; 8 — cortex; 9 — lymphoid follicle; 10 — medulla; 11 — arteries; 12 — veins; 13 — efferent lymphatic vessels; 14 — afferent lymphatic vessels (after M. R. Sapin)

Afferent vessels open into the marginal sinus, whereas efferent lymphatic vessels originate from the hilar sinus. The cortex occupies a greater area in visceral lymph nodes than in somatic ones. Nodes of various groups differ in their cellular composition: stem cells (hemocytoblasts), which determine the intensity of lymphopoiesis, are relatively more abundant in somatic nodes during youth, and in visceral nodes during middle and old age.

As lymph flows through the lymph nodes, it is filtered of foreign particles as well as microbes, should they enter the body, and becomes enriched with cellular elements. Lymph nodes act as active biological filters that retain and phagocytose about 90% of all foreign particles, including Bacteria, delivered by the lymph. Immune bodies are produced within the lymph nodes. They can also serve as a depot for the flowing lymph.

Lymph is a transparent fluid containing lymphocytes and a small number of eosinophils and monocytes (see p. 26). Its protein and cellular composition changes significantly along its pathway through the lymphatic system. For instance, peripheral lymphatic vessels contain 0.49–0.69% protein, predominantly albumin, whereas the thoracic duct contains 2 to 4.5%. Regarding cellular composition, D. A. Zhdanov categorized lymph into peripheral (Cell-poor, which has not yet passed through the first lymph node), intermediate, and central (which has already passed through all nodes and has been enriched with cellular elements from their lymphoid tissue). The latter type represents the lymph of the thoracic and right lymphatic ducts; 1 mm³ of it contains from 2,000 to 20,000 lymphocytes and 500–12,250 leukocytes.

Organs of Immunogenesis

Organs of immunogenesis are subdivided into Primary and secondary. The former include the Thymus, Tonsils, and Red Bone Marrow; the latter include the lymph nodes, Spleen, and aggregates of lymphoid tissue within organs. During the Embryonic period, lymphocytes begin to develop in the thymus, from where they migrate to populate the spleen and lymph nodes (see p. 319).

The thymus, which is the central organ of the lymphoid system, is located in the upper anterior mediastinum. It lies directly posterior to the manubrium of the Sternum, extending inferiorly to the level of the 4th costal cartilage, and superiorly (especially in newborns) projecting with the apices of its lobes through the superior thoracic aperture into the cervical region (see Figs. 83, 144).

Owing to the soft consistency of the thymus, its external shape largely depends on the Morphology of adjacent structures. It is better developed in males than in females. The weight of the gland reaches 10–15 g in newborns, 25–30 g at 14–16 years of age, and subsequently undergoes involution. In some cases, the thymus persists into old age, in which event the body exhibits heightened sensitivity to certain toxic substances, particularly chloroform.

The thymus consists of two lobes, each representing a vertically elongated structure. They expand inferiorly and taper superiorly. Both lobes are entirely independent and merely lie adjacent to each other, lacking an isthmus like the lobes of The Thyroid Gland. Each lobe of the gland is subdivided into lobules measuring 4–10 mm in diameter.

On cross-section, two layers of the gland are discernible: the cortical layer (outer, darker) and the medullary layer (deep, lighter). The glandular tissue (parenchyma) is represented by a loose network of epithelial stellate cells. Lymphocytes reside within the meshes of this network. They are more abundant in the cortex than in the medulla. Aggregations of degenerating epithelial cells in the medulla form the so-called Hassall's corpuscles. Following Puberty, the cortex of the thymus undergoes involution, resulting in a reduction of lobule volume. The medulla undergoes less pronounced changes. Because the gland possesses a well-defined capsule, its shape is preserved even after the complete replacement of all glandular elements by adipose tissue.

The thymus performs multiple functions. As an endocrine organ, it secretes a hormone—thymosin—which regulates carbohydrate and calcium METABOLISM in the Body. Removal of this gland in growing animals causes growth retardation and a decrease in calcium salt content within bones, rendering the skeletal bones less robust. Thus, the thymus is important for regulating calcium metabolism in the body and controls skeletal growth (primarily During the first 10–15 years of life).

However, The primary function of the thymus is participation in immunological reactions. It produces T-lymphocytes (thymus-dependent), which mediate cellular and humoral immunity, unlike B-lymphocytes, which are not developmentally linked to the thymus and, according to some data, execute solely humoral immunity processes.

Although the thymus is commonly thought to shrink with age, its linear dimensions remain relatively stable. Into adulthood, it preserves relatively unchanged ultrastructures of both the cortex and medulla, as well as the connective tissue stroma.

Lymphocytopoiesis processes in the cortex proceed just as they do in childhood, and the medulla provides a similarly favorable microenvironment for T-lymphocytes. Although parenchymal tissue is partially replaced by adipose tissue, the remaining parenchymal islands retain their regenerative capacity, forming glandular structures and Hassall's corpuscles.

Red bone marrow. In adults, it is located in the spongy substance of flat bones, vertebral bodies, the epiphyses of long bones, and the bones of the wrist and tarsus. It consists of reticular tissue, among the cells of which hematopoietic stem cells are situated. Their number is 50 for every 10⁵ reticular tissue cells. The development of bone marrow and Bone tissue is mutually interconnected.

The spleen (Fig. 79). It is located in the left hypochondrium. Its upper border is projected at the level of the 10th–11th thoracic vertebrae, and the lower border at the 1st–2nd lumbar vertebrae (in children, from the 8th–9th thoracic to the 1st lumbar). The weight of the spleen in men aged 30–59 is 109–122 g, and in women of the same age, 97–102 g. The organ's mass changes with age: it decreases from 20 to 29 years, stabilizes between 30 and 59 years, and decreases again after 60.

The spleen has two surfaces: a convex (diaphragmatic) and a concave (visceral), featuring the hilum where blood Vessels and nerves pass. The visceral surface of the spleen is in contact with The Stomach, left Adrenal gland, left Kidney, tail of the pancreas, and the left colic flexure. The spleen is covered on all sides by a serous membrane—the Peritoneum, beneath which lies a connective tissue capsule containing elastic and smooth muscle fibers that help regulate the spleen's volume. Trabeculae extend inward from the capsule, creating a framework between which the splenic parenchyma (pulp) is located. It contains lymphoid tissue inclusions in the form of white islands (accounting for 17–19% of the organ's volume), where lymphocytes are produced.

Due to an extensive network of sinuses and specialized sphincters in the arterioles and venules of the spleen, a significant volume of blood can be pooled and subsequently driven into the bloodstream by the contraction of smooth muscle cells in the capsule and trabeculae.

If the bone marrow is the birthplace of erythrocytes, the spleen is the site of their destruction. Regarding white Blood Cells, it acts as a hematopoietic organ; its stem cells participate in lymphocytopoiesis. Under extreme conditions (for instance, during severe anemia in childhood), it also gives rise to foci of extramedullary erythropoiesis (erythrocyte production outside the red bone marrow).

Tonsils. Palatine, tubal, lingual, and pharyngeal tonsils are distinguished, all located in the Oral Cavity and Pharynx. They consist of reticular tissue infiltrated with lymphocytes and other cellular elements, featuring compact cellular clusters known as follicles.

Aggregated and solitary lymphatic nodules. They are located in the walls of the digestive and respiratory systems: solitary nodules are found in the mucosa and submucosa of the pharynx, Esophagus, stomach, small and large intestines, Gallbladder, Larynx, Trachea, and major Bronchi; aggregated nodules are primarily located in the Small Intestine (especially abundant in the ileum) and the Appendix. They consist of lymphoid tissue (supported by a reticular framework) that forms lymphatic follicles.

The total mass of The Immune System organs (excluding the bone marrow) is 1.5–2 kg. Lymph nodes account for about 1% of body weight.

The condition of the immune system organs, which determines the body's immunity, depends on living and upbringing conditions, including the Specifics of the physical activity regimen (see p. 596)