Human Anatomy - Lecture Course - Kostylenko Yu.P. 2015

Immune and Lymphatic Systems

7.1. Importance of The Immune System.

7.2. CHARACTERISTICS OF THE Organs of the Immune System.

7.3. General Anatomy of The Lymphatic system.

7.4. Lymph Nodes AND Vessels of the HEAD and Neck.

7.1 Structure/19.html">The Importance of the Immune System

The immune system integrates organs and Tissues that protect the body against genetically foreign Cells and substances entering from the external environment or generated within the body. The organs of the immune system safeguard the constancy of the body's internal environment throughout an individual's lifetime. These organs produce immunocompetent cells (lymphocytes, plasmocytes), incorporate them into the immune process, and ensure the recognition and destruction of foreign substances (Antigens).

Depending on their role in immunogenesis, the organs of the immune system are divided into central and peripheral. The Central Organs of the Immune System include the Cytology/practical/86.html">Red Bone Marrow and the thymus; antigen-independent proliferation of lymphocytes takes place in these organs.

7.2 Characteristics of the Organs of the Immune System

In the human immunogenesis system, bone marrow is currently viewed by some researchers as an analogue of the bursa of Fabricius—a cellular cluster in the wall of the cloacal region of the gut in birds, where B-lymphocytes are formed from stem cells.

The differentiation of T-lymphocytes (thymus-dependent), formed from stem cells entering this organ, occurs in the thymus. Subsequently, both lymphocyte populations migrate to the Peripheral Organs of the Immune System, which include the Tonsils, lymphoid nodules, lymph nodes, and spleen. The function of the peripheral organs of the immune system is regulated by the central Organs of Immunogenesis.

T-lymphocytes populate the thymus-dependent Zones of the lymph nodes (paracortical zone) and the spleen (periarterial region of the lymphoid nodules), providing both Cell-mediated Immunity through the accumulation and deployment of sensitized lymphocytes, and humoral immunity (via the Synthesis of specific Antibodies).

B-lymphocytes are precursors of antibody-producing cells: plasmocytes and lymphocytes. They migrate to the B-dependent zones of the lymph nodes (lymphoid nodules, medullary cords) and the spleen (lymphoid nodules, except for their periarterial region). B-lymphocytes mediate humoral immunity, in which the primary role belongs to Blood, lymph, and glandular secretions containing antibodies that participate in immune reactions.

The organs of the immune system share A number of distinct features:

1 - early embryonic development (anlage);

2 - functional maturity by the time of birth;

3 - stroma formed by reticular tissue, and parenchyma by lymphoid tissue;

4 - localization of most immune system organs in protected anatomical sites.

Red Bone Marrow. The bone marrow Functions simultaneously as an organ of

hematopoiesis and of the immune system. A distinction is made between red bone marrow, which in adults is located in the spongy spaces of flat and short bones and the epiphyses of long bones, and yellow bone marrow, which fills the medullary cavities of the diaphyses of long bones. The total mass of bone marrow in an adult is about 2.5–3 kg (4.5–4.7% of body weight). About half of this total is red bone marrow, and the rest is yellow. Red bone marrow derives from myeloid tissue, which comprises reticular tissue and hematopoietic elements. It contains hematopoietic stem cells, which are precursors to all BLOOD AND LYMPH cells.

In a general biological sense, the term "stem cell" implies the capacity of these cellular elements for self-renewal of the population while simultaneously differentiating toward a particular clone. In the red bone marrow, the division of a parent hematopoietic stem cell (HSC) yields one cell identical in all properties to the parent and one unipotent hemistem cell, which gives rise to a specific type of formed blood element. The process of stem Cell Differentiation is driven by multiple factors, among which the microenvironment plays a paramount role.

Yellow bone marrow consists predominantly of adipose tissue that has replaced reticular tissue. Hematopoietic elements are absent in yellow bone marrow; however, under conditions of severe blood loss, foci of hematopoiesis may emerge within it.

The thymus is a central organ of immunogenesis. The differentiation of T-lymphocytes, The production of the thymic humoral factor, and the Synthesis of the hormone thymosin take place within the thymus.

The thymus is located in the superior Mediastinum, posterior to the manubrium and the upper part of the body of the Sternum. It is bounded laterally by the pleural sacs, inferiorly by the Pericardium, and posteriorly by the aortic arch and the SUPERIOR VENA CAVA. It has a pinkish-gray color and a soft consistency, typically consisting of two unequal, pyramid-shaped lobes with their apexes directed upward. Frequently, the lobes of the gland extend into the neck, where they may reach The Thyroid Gland.

The thymus has a lobular structure. The lobules are separated by Connective Tissue septa extending from its capsule. Each lobule is differentiated into a cortex and a medulla. The cortex is characterized by a high concentration of lymphocytes, which are distributed diffusely and do not form follicles. In the medulla, lymphocytes are sparse, and there are clusters of reticular cells known as thymic corpuscles, or Hassall's corpuscles.

The average mass of the thymus at birth is 15 g, reaching 30 g by the age of 15. After 20 years of age, the thymus undergoes a reduction in size, with its parenchyma being replaced by adipose and connective tissue—a process known as age-related involution of the thymus.

In certain cases, the thymus does not undergo age-related involution, or its regression is significantly slowed down. This condition is known as status thymolymphaticus and is typically accompanied by a deficiency in Adrenal Cortex Hormones. Such individuals are prone to infectious diseases, tumor processes, and intoxications, and they tolerate anesthesia poorly.

Sudden, rapid, or accidental involution of the thymus may occur due to the body being exposed to strong stressors (trauma, intoxication, infection, starvation), in which case the individual also exhibits immunodeficient states.

The Blood supply to the thymus is provided by the inferior thyroid, internal thoracic, and pericardiacophrenic Arteries. Lymph drainage is directed toward the parasternal, tracheobronchial, and anterior mediastinal nodes.

The spleen is an organ where lymphoid tissue integrates with the Circulatory system. THE POSITION OF the spleen in this system is analogous to that of Lymph Nodes in the lymphatic system, which is why some authors figuratively refer to it as a "large lymph node."

The spleen acts as a blood reservoir; on the one hand, it is a site for the destruction of erythrocytes and platelets, and on the other hand, for lymphocytopoiesis. The protective function of the spleen and its involvement in immune responses are closely associated with the production of lymphocytes.

The spleen is an unpaired organ located in the left hypochondriac region, shaped like a flattened and elongated hemisphere. Its convex diaphragmatic surface abuts the Diaphragm, while the concave visceral surface borders the left Kidney, Stomach, and colon. The hilum is located on the visceral surface, serving as the entry point for the splenic artery and the exit point for the splenic vein. The long axis of the spleen corresponds to the 10th rib, with the posterior pole facing THE Vertebral Column. The superior border of the spleen is sharp, whereas the inferior border is blunt. The length of the spleen typically ranges from 10–14 cm, its width from 6–10 cm, and its thickness from 3–4 cm. The spleen is an intraperitoneal organ, from which peritoneal ligaments extend to The Stomach and kidney.

The spleen is surrounded by a dense fibrous capsule; inside, much like in a lymph node, there are connective tissue trabeculae through which arteries and Veins run. The parenchyma of the spleen is called the pulp. It is subdivided into white pulp and red pulp. The red pulp, located between the venous sinuses, consists of a reticular tissue meshwork filled with erythrocytes, leukocytes, lymphocytes, and macrophages.

The white pulp is an aggregate of lymphoid tissue located in the adventitia of arteries in the form of nodules and periarterial lymphatic sheaths.

Both types of pulp differ functionally. The red pulp performs phagocytosis of incoming corpuscular blood elements (erythrocytes, platelets, Bacteria, tumor cells). The Significance of the white pulp lies in the immunological monitoring of blood composition.

The hollow organs of the respiratory and digestive systems contain numerous accumulations of lymphoid tissue that prevent infectious agents from the external environment from entering the internal environment via airborne or alimentary routes. These include Solitary lymphoid nodules, lymphoid aggregates of the Small Intestine, and lymphoid nodules of the vermiform Appendix.

Solitary lymphoid nodules. Lymphoid nodules are found within the thickness of the mucous membrane and submucosa of the digestive organs (Pharynx, Esophagus, stomach, small and large intestines, Gallbladder), respiratory organs (Larynx, Trachea, main, lobar, and segmental Bronchi), as well as in the walls of the Ureters, Urinary Bladder, and Urethra. The number of lymphoid nodules is quite large. In the wall of the small intestine in children, the number of nodules ranges from 1,000 to 5,000; in the walls of the Large Intestine, from 1,800 to 7,300; in the walls of the trachea, from 100 to 180; and in the wall of the urinary bladder, from 25 to 100.

Lymphoid plaques (Peyer's patches) are nodular accumulations of lymphoid tissue located in the wall of the ileum. They lie within the thickness of the mucous membrane and submucosa. As a rule, these patches are situated on the side opposite to the mesenteric border of the intestine. The number of patches during the period of their maximum development (in children and adolescents) is 30–80. The length of the patches ranges from 0.2 to 15 cm, and their width is 0.2–1.5 cm. Lymphoid plaques consist of lymphoid nodules, the number of which in a single patch varies from 5–10 to 100–150 or more. The sizes of the lymphoid nodules within the patches range from 0.5 to 2 mm.

Tonsils are accumulations of lymphoid tissue along the periphery of the fauces, forming the pharyngeal lymphoid ring (Waldeyer's ring), which protects the body from the penetration of antigens via airborne and (to a lesser extent) alimentary routes. They appear as diffuse accumulations of lymphoid tissue containing smaller, denser cell masses known as lymphoid nodules. The lingual, pharyngeal, palatine, and tubal tonsils are distinguished.

Milk spots of the greater omentum are located within the thickness of the greater omentum along the course of Blood Vessels. Their sizes vary between 1–5 mm. Macrophages are the predominant cellular elements within them, providing grounds for classifying them as local outposts of the immune system. They perform immune surveillance over the antigenic COMPOSITION OF THE peritoneal fluid and participate in local defense reactions.

7.3 General Anatomy of the Lymphatic System

According to modern concepts regarding the Functional Significance of the lymphatic system, it should be regarded as an integral component of the body's defense system. In humans, the lymphatic system is closely connected with The Vascular System and comprises capillaries, Lymphatic vessels, nodes, trunks, and ducts through which lymph flows from its site of formation to the confluence of the internal jugular and subclavian veins, forming the venous angle.

Lymph (from Latin - clear Water) is a colorless fluid whose composition resembles Blood Plasma, containing 3–4% Proteins, 0.1% sugars, 0.9% salts, and 2x10³–2x10⁴ lymphocytes.

The Main Functions of the lymphatic system include: 1 – protective; 2 – drainage; 3 – transport. Thus, in response to The entry of foreign substances (antigens) into the body, lymphocytes and Antibodies Are Formed in the organs of the lymphatic system, and the lymphatic pathways transport them to the site of injury. The lymphatic system participates in neutralizing cell breakdown products, and foreign substances are trapped within the lymph nodes. Impairment of lymphatic system functions leads to a decrease in the body's protective properties.

Lymphatic vessels drain excess water and dissolved crystalloids from tissues; at the same time, the lymphatic system absorbs and transports colloidal substances and proteins. A specific property of lymphatic capillaries is their permeability to cells and various foreign particles. Bacteria entering Lymphatic vessels and tumor cells are carried along by the lymph flow. Thus, the lymphatic system participates in the spread of pathological processes. Metastasis of malignant tumors occurs via lymphatic vessels.

The lymphatic system is extensively branched throughout the body; however, there are a number of organs where Structural components of the lymphatic system are absent, including the Brain AND SPINAL cord, Eyeball, Inner ear, bone marrow, spleen parenchyma, Placenta, Cartilage, and hard Tissues of the tooth. In most organs lacking a lymphatic system, other biological fluids (CEREBROSPINAL FLUID, endolymph) perform a similar role.

Lymphatic capillaries and vessels. The initial link of the lymphatic system is represented by lymphatic capillaries. Colloidal protein solutions and aqueous crystalloid solutions are absorbed from tissues into the lymphatic capillaries, and foreign particles (fragments of destroyed cells, microbial bodies) are drained from tissues.

Unlike blood capillaries, lymphatic capillaries have a larger diameter (up to 0.2 mm), are blind-ended (resembling test tubes or "glove fingers"), and their wall consists of a single layer of endothelial cells, lacking a basement membrane. The endothelial cells of lymph capillaries are 4–5 times larger than those in blood capillaries. These Structural Features of the lymphatic Capillary Wall facilitate the penetration of dissolved substances into them (Fig. 7.1).

Within organs, lymphatic capillaries form networks (two- and three-dimensional). By merging with one another, lymphatic capillaries form lymphatic vessels.

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Fig. 7.1 Lymphatic vessels:

1 — lymphatic capillaries;

2 — lymphatic trunks;

3 — Valves.

Compared to capillaries, lymphatic vessels have thicker walls and are equipped with valves formed by folds of the tunica intima containing a small amount of connective tissue. Due to the presence of these valves, lymph flows in only one direction through the vessels — from the periphery (capillaries) toward lymph nodes, trunks, and ducts.

In small lymphatic vessels, the intervals between valves are 2–3 mm; in larger vessels, 6–8 mm; and in lymphatic trunks, 12–15 mm. At the sites of the valves, lymphatic vessels form dilations, whereas in the segments between the valves, they narrow. This alternation of dilations and constrictions gives lymphatic vessels a beaded appearance.

The segment of a lymphatic vessel located between two adjacent valves is defined as the Structural and functional unit of the lymphatic bed, known as a lymphangion. A lymphangion comprises three structural components: the muscular cuff, the valve sinus region, and the valve attachment site.

The functional Significance of the lymphangion is determined by its role in regulating the centripetal propulsion of lymph.

Topographically, lymphatic vessels are divided into superficial (located external to the superficial fascia of The Human Body and running close to subcutaneous veins) and deep, which typically accompany neurovascular bundles.

Through lymphatic vessels, lymph from organs and body parts is directed toward the lymph nodes.

Lymph nodes serve as biological filters for lymph, organs of lymphocytopoiesis, and sites of antibody production. They are small, rounded, bean-shaped, or nodular bodies ranging from 2 to 20 mm in size. According to various authors, the total number of lymph nodes in humans ranges from 460 to 600–700. Their number varies individually and decreases with age as some lymph nodes are replaced by connective or adipose tissue.

Externally, each lymph node is covered by a connective tissue capsule from which thin partitions (trabeculae) extend into its interior. Inside the lymph node, There is a stroma (formed by reticular tissue) and a parenchyma represented by lymphoid tissue. The parenchyma of the node is divided into the cortex and the medulla. The cortex contains lymphatic follicles, which are accumulations of lymphocytes.

Between the capsule, trabeculae, and lymphatic follicles lie slit-like spaces called sinuses, which serve as pathways for lymph Circulation through the node.

Lymph enters the lymph node via afferent lymphatic vessels that approach the convex side of the node and drain into the subcapsular (marginal) sinus. Subsequently, via a system of sinuses, the lymph reaches the hilar sinus. One or two efferent lymphatic vessels emerge from the hilar sinus and leave the lymph node.

Within lymph nodes, the composition of lymph changes: lymphocytes are added, foreign particles are retained, and bacteria and tumor cells are trapped. Thus, purification of the lymph takes place. Consequently, the primary functions of lymph nodes are protective and barrier-based.

Through efferent lymphatic vessels, lymph flows from one set of nodes to subsequent lymph nodes lying along its pathway, or to collector vessels, namely lymphatic trunks and ducts.

Along its pathway from any given organ, lymph passes through at least one lymph node, and more frequently through several. For example, on its pathway from the stomach, lymph passes through 6–8 nodes, whereas from the kidney it passes through 6–10 lymph nodes. The first lymph node encountered is referred to as a first-order node, while subsequent ones are called second-, third-, and so on. Conversely, vessels draining lymph from organs sometimes bypass nodes and drain directly into lymphatic collectors. The literature describes cases where lymphatic vessels from the thyroid gland, esophagus (most frequently), Heart, Pancreas, and Liver empty directly into the Thoracic duct. Such instances create particularly favorable conditions for the Early Development of metastasis (the spread of a tumor process to other organs) when the respective organs are affected by malignant tumors.

Lymph nodes located closest to an organ (or body region) are called regional nodes. They are the first to respond to a pathological process occurring within the organ (such as inflammation or a malignant neoplasm).

Taking into account their topographical features in the human body, about 150 regional lymph node groups are distinguished. Based on the aforementioned, lymph nodes are named either according to their anatomical Location (lumbar, axillary) or, in a number of cases, after a nearby blood vessel.

Lymph nodes lying in the immediate vicinity of Internal Organs are conventionally called visceral nodes. These include groups such as the mediastinal, bronchopulmonary, and juxtauterine nodes. Lymph nodes located on the walls of cavities are called parietal nodes. The latter include the parasternal, intercostal, and superior diaphragmatic nodes. In certain areas of the body, lymph nodes are arranged in two layers, one group overlying the other, typically separated by a fascia. In such cases, nodes lying superficial to the fascia are termed superficial, while those beneath it are termed deep.

Lymphatic trunks and ducts. Lymph from each body region, after passing through lymph nodes, collects into one of the major collector vessels. These include the right and left lumbar trunks (which drain lymph from the lower extremities and pelvic organs). Uniting at the level of the 12th thoracic to 2nd lumbar vertebrae, they give rise to the thoracic duct, which also receives the intestinal trunk (inconstant), left bronchomediastinal, left jugular, and left subclavian trunks.

As mentioned above, the thoracic duct empties into the left venous angle. Thus, the thoracic duct collects lymph from both lower extremities (lumbar trunks), the Abdominal cavity (intestinal trunk), the left half of the Thorax (left bronchomediastinal trunk), the left upper extremity (left subclavian trunk), and the left half of the head and neck (left jugular trunk).

Uniting with one another, the right jugular, subclavian, and bronchomediastinal trunks give rise to the Right lymphatic duct. The right lymphatic duct is considerably smaller than the thoracic duct, empties into the right venous angle, and collects lymph from the right upper extremity (right subclavian trunk), the right half of the thorax (right bronchomediastinal trunk), and the right half of the head and neck (right jugular trunk) (Fig. 7.2).

7.4 Lymph nodes and vessels of the head and neck

Lymph nodes of the head are located mainly along a conventional line separating the head from the neck and are subdivided into: 1 — occipital, 2 — parotid (superficial and deep), 3 — mastoid, 4 — submandibular, 5 — submental, 6 — facial (buccal).

Lymph drainage from the head occurs as follows: from the frontal region, into superficial parotid lymph nodes; from the parietal and temporal regions, into parotid nodes; and from the occipital region, into occipital nodes. Lymph from the lower lip and the lateral margin of the upper lip drains into the submandibular nodes; from the medial part of the upper lip, into the submental nodes; from the walls of the Orbit, into the facial nodes; and from the parotid gland, into the parotid lymph nodes.

Fig. 7.2. Diagram of collecting lymphatic vessels:

1 - thoracic duct;

2 - lumbar trunks;

3 - intestinal trunk;

4 - left subclavian trunk;

5 - left jugular trunk;

6 - right lymphatic duct.

Lymph drainage from the sublingual and submandibular Salivary Glands flows into the submandibular nodes; from the Tongue, into the submandibular and deep lateral cervical nodes; and from the lower dental arch, into the submandibular nodes. From the incisors and canines of the upper jaw, lymph drains into the submental nodes, whereas from the molars and premolars, it drains into the submandibular and parotid lymph nodes.

From the aforementioned lymph nodes of the head, lymph collects into the superficial cervical lymph nodes, which are further subdivided into: 1 - an anterior group (along the course of the Anterior jugular vein); 2 - a lateral group (along the course of the External Jugular Vein); 3 - a posterior group (along the posterior border of the trapezius Muscle). Subsequently, lymph drains into the deep cervical lymph nodes, which include: 1 - an anterior group (prelaryngeal, thyroid, and pretracheal); 2 - a lateral group (along the course of the Internal jugular vein). From the deep cervical lymph nodes, lymph flows into the right and left jugular trunks.