THE LYMPHATIC SYSTEM consists (1) of complex capillary networks which collect the lymph in the various organs and tissues; (2) of an elaborate system of collecting vessels which conduct the lymph from the capillaries to the large veins of the neck at the junction of the internal jugular and subclavian veins, where the lymph is poured into the blood stream; and (3) lymph nodes or nodes which are interspaced in the pathways of the collecting vessels filtering the lymph as it passes through them and contributing lymphocytes to it. The lymphatic capillaries and collecting vessels are lined throughout by a continuous layer of endothelial cells, forming thus a closed system. The lymphatic vessels of the small intestine receive the special designation of lacteals or chyliferous vessels; they differ in no respect from the lymphatic vessels generally excepting that during the process of digestion they contain a milk-white fluid, the chyle.
The Development of the Lymphatic Vessels.—The lymphatic system begins as a series of sacs at the points of junction of certain of the embryonic veins. These lymph-sacs are developed by the confluence of numerous venous capillaries, which at first lose their connections with the venous system, but subsequently, on the formation of the sacs, regain them. The lymphatic system is therefore developmentally an offshoot of the venous system, and the lining walls of its vessels are always endothelial.
In the human embryo the lymph sacs from which the lymphatic vessels are derived are six in number; two paired, the jugular and the posterior lymph-sacs; and two unpaired, the retroperitoneal and the cisterna chyli. In lower mammals an additional pair, subclavian, is present, but in the human embryo these are merely extensions of the jugular sacs.
The position of the sacs is as follows: (1) jugular sac, the first to appear, at the junction of the subclavian vein with the primitive jugular; (2) posterior sac, at the junction of the iliac vein with the cardinal; (3) retroperitoneal, in the root of the mesentery near the suprarenal nodes; (4) cisterna chyli, opposite the third and fourth lumbar vertebrae. From the lymph-sacs the lymphatic vessels bud out along fixed lines corresponding more or less closely to the course of the embryonic bloodvessels. Both in the body-wall and in the wall of the intestine, the deeper plexuses are the first to be developed; by continued growth of these the vessels in the superficial layers are gradually formed. The thoracic duct is probably formed from anastomosing outgrowths from the jugular sac and cisterna chyli. At its connection with the cisterna chyli it is at first double, but the two vessels soon join.
All the lymph-sacs except the cisterna chyli are, at a later stage, divided up by slender connective tissue bridges and transformed into groups of lymph nodes. The lower portion of the cisterna chyli is similarly converted, but its upper portion remains as the adult cisterna.
Lymphatic Capillaries.—The complex capillary plexuses which consist of a single layer of thin flat endothelial cells lie in the connective-tissue spaces in the various regions of the body to which they are distributed and are bathed by the intercellular tissue fluids. Two views are at present held as to the mode in which the lymph is formed: one being by the physical processes of filtration, diffusion, and osmosis, and the other, that in addition to these physical processes the endothelial cells have an active secretory function. The colorless liquid lymph has about the same composition as the blood plasma. It contains many lymphocytes and frequently red blood corpuscles. Granules and bacteria are also taken up by the lymph from the connective-tissue spaces, partly by the action of lymphocytes which pass into the lymph between the endothelial cells and partly by the direct passage of the granules through the endothelial cells.
The lymphatic capillary plexuses vary greatly in form; the anastomoses are usually numerous; blind ends or cul-de-sacs are especially common in the intestinal villi, the dermal papillae and the filiform papillae of the tongue. The plexuses are often in two layers: a superficial and a deep, the superficial being of smaller caliber than the deep. The caliber, however, varies greatly in a given plexus from a few micromillimeters to one millimeter. The capillaries are without valves.
Distribution.—The Skin.—Lymphatic capillaries are abundant in the dermis where they form superficial and deep plexuses, the former sending blind ends into the dermal papillae. The plexuses are especially rich over the palmar surface of the hands and fingers and over the plantar surface of the feet and toes. The epidermis is without capillaries. The conjunctiva has an especially rich plexus.
The subcutaneous tissue is without capillaries.
The tendons of striated muscle and muscle sheaths are richly supplied. In muscle, however, their existence is still disputed.
The periosteum of bone is richly supplied and they have been described in the Haversian canals. They are absent in cartilage and probably in bone marrow.
The joint capsules are richly supplied with lymphatic capillaries, they do not, however, open into the joint cavities.
Beneath the mesothelium lining of the pleural, peritoneal and pericardial cavities are rich plexuses; they do not open into these cavities.
The alimentary canal is supplied with rich plexuses beneath the epithelium, often as a superficial plexus in the mucosa and a deeper submucosal plexus. Cul-de-sacs extend into the filiform papillae of the tongue and the villi of the small intestine. Those portions of the alimentary canal covered by peritoneum, have in addition a subserous lymphatic capillary plexus beneath the mesothelium.
The salivary nodes are supplied with lymphatic capillaries.
The liver has a rich subserous plexus in the capsule and also extensive plexuses which accompany the hepatic artery and portal vein. The lymphatic capillaries have not been followed into the liver lobules. The lymph from the liver forms a large part of that which flows through the thoracic duct. The gall-bladder and bile ducts have rich subepithelial plexuses and the former a subserous plexus.
The spleen has a rich subserous set and a capsular set of lymphatic capillaries. Their presence in the parenchyma is uncertain.
The nasal cavity has extensive capillary plexuses in the mucosa and submucosa.
The trachea and bronchi have plexuses in the mucosa and submucosa but the smaller bronchi have only a single layer. The capillaries do not extend to the air-cells. The plexuses around the smaller bronchi connect with the rich subserous plexus of the lungs in places where the veins reach the surface.
Lymphatics have been described in the thyroid node and in the thymus.
The adrenal has a superficial plexus divided into two layers, one in the loose tissue about the node and the other beneath the capsule. Capillaries have also been described within the parenchyma.
The kidney is supplied with a coarse subserous plexus and a deeper plexus of finer capillaries in the capsule. Lymphatics have been described within the substance of the kidney surrounding the tubules.
The urinary bladder has a rich plexus of lymphatic capillaries just beneath the epithelial lining, also a subserous set which anastomoses with the former through the muscle layer. The submucous plexus is continuous with the submucous plexus of the urethra.
The prostate has a rich lymphatic plexus surrounding the node and a wide-meshed subcapsular plexus.
The testis has a rich superficial plexus beneath the tunica albuginea. The presence of deep lymphatics is disputed.
The uterus is provided with a subserous plexus, the deeper lymphatics are uncertain. Subepithelial plexuses are found in the vagina.
The ovary has a rich superficial plexus and a deep interstitial plexus.
The heart has a rich subserous plexus beneath the epicardium. Lymphatic capillaries have also been described beneath the endocardium and throughout the muscle.
Lymphatic capillaries are probably absent in the central nervous system, the meninges, the eyeball (except the conjunctiva), the orbit, the internal ear, within striated muscle, the liver lobule, the spleen pulp and kidney parenchyma. They are entirely absent in cartilage. In many places further investigation is needed.
Lymphatic Vessels.—The lymphatic vessels are exceedingly delicate, and their coats are so transparent that the fluid they contain is readily seen through them. They are interrupted at intervals by constrictions, which give them a knotted or beaded appearance; these constrictions correspond to the situations of valves in their interior. Lymphatic vessels have been found in nearly every texture and organ of the body which contains bloodvessels. Such non-vascular structures as cartilage, the nails, cuticle, and hair have none, but with these exceptions it is probable that eventually all parts will be found to be permeated by these vessels.
Structure of Lymphatic Vessels.—The larger lymphatic vessels are each composed of three coats. The internal coat is thin, transparent, slightly elastic, and consists of a layer of elongated endothelial cells with wavy margins by which the contiguous cells are dovetailed into one another; the cells are supported on an elastic membrane. The middle coat is composed of smooth muscular and fine elastic fibers, disposed in a transverse direction. The external coat consists of connective tissue, intermixed with smooth muscular fibers longitudinally or obliquely disposed; it forms a protective covering to the other coats, and serves to connect the vessel with the neighboring structures. In the smaller vessels there are no muscular or elastic fibers, and the wall consists only of a connective-tissue coat, lined by endothelium. The thoracic duct has a more complex structure than the other lymphatic vessels; it presents a distinct subendothelial layer of branched corpuscles, similar to that found in the arteries; in the middle coat there is, in addition to the muscular and elastic fibers, a layer of connective tissue with its fibers arranged longitudinally. The lymphatic vessels are supplied by nutrient vessels, which are distributed to their outer and middle coats; and here also have been traced many non-medullated nerves in the form of a fine plexus of fibrils.
The valves of the lymphatic vessels are formed of thin layers of fibrous tissue covered on both surfaces by endothelium which presents the same arrangement as on the valves of veins. In form the valves are semilunar; they are attached by their convex edges to the wall of the vessel, the concave edges being free and directed along the course of the contained current. Usually two such valves, of equal size, are found opposite one another; but occasionally exceptions occur, especially at or near the anastomoses of lymphatic vessels. Thus, one valve may be of small size and the other increased in proportion.
In the lymphatic vessels the valves are placed at much shorter intervals than in the veins. They are most numerous near the lymph nodes, and are found more frequently in the lymphatic vessels of the neck and upper extremity than in those of the lower extremity. The wall of the lymphatic vessel immediately above the point of attachment of each segment of a valve is expanded into a pouch or sinus which gives to these vessels, when distended, the knotted or beaded appearance already referred to. Valves are wanting in the vessels composing the plexiform net-work in which the lymphatic vessels usually originate on the surface of the body.
Lymph Nodes (lymphonodeulae).—The lymph nodes are small oval or bean-shaped bodies, situated in the course of lymphatic and lacteal vessels so that the lymph and chyle pass through them on their way to the blood. Each generally presents on one side a slight depression—the hilus—through which the bloodvessels enter and leave the interior. The efferent lymphatic vessel also emerges from the node at this spot, while the afferent vessels enter the organ at different parts of the periphery. On section a lymph node displays two different structures: an external, of lighter color—the cortical; and an internal, darker—the medullary. The cortical structure does not form a complete investment, but is deficient at the hilus, where the medullary portion reaches the surface of the node; so that the efferent vessel is derived directly from the medullary structures, while the afferent vessels empty themselves into the cortical substance.
Structure of Lymph Nodes.—A lymph Node consists of (1) a fibrous envelope, or capsule, from which a frame-work of processes (trabeculae) proceeds inward, imperfectly dividing the Node into open spaces freely communicating with each other; (2) a quantity of lymphoid tissue occupying these spaces without completely filling them; (3) a free supply of bloodvessels, which are supported in the trabeculae; and (4) the afferent and efferent vessels communicating through the lymph paths in the substance of the node. The nerves passing into the hilus are few in number and are chiefly distributed to the bloodvessels supplying the node.
The capsule is composed of connective tissue with some plain muscle fibers, and from its internal surface are given off a number of membranous processes or trabeculae, consisting, in man, of connective tissue, with a small admixture of plain muscle fibers; but in many of the lower animals composed almost entirely of involuntary muscle. They pass inward, radiating toward the center of the node, for a certain distance—that is to say, for about one-third or one-fourth of the space between the circumference and the center of the node. In some animals they are sufficiently well-marked to divide the peripheral or cortical portion of the node into a number of compartments (so-called follicles), but in man this arrangement is not obvious. The larger trabeculae springing from the capsule break up into finer bands, and these interlace to form a mesh-work in the central or medullary portion of the node. In these spaces formed by the interlacing trabeculae is contained the proper node substance or lymphoid tissue. The node pulp does not, however, completely fill the spaces, but leaves, between its outer margin and the enclosing trabeculae, a channel or space of uniform width throughout. This is termed the lymph path or lymph sinus. Running across it are a number of finer trabeculae of retiform connective tissue, the fibers of which are, for the most part, covered by ramifying cells.
On account of the peculiar arrangement of the frame-work of the organ, the node pulp in the cortical portion is disposed in the form of nodules, and in the medullary part in the form of rounded cords. It consists of ordinary lymphoid tissue, being made up of a delicate net-work of retiform tissue, which is continuous with that in the lymph paths, but marked off from it by a closer reticulation; it is probable, moreover, that the reticular tissue of the node pulp and the lymph paths is continuous with that of the trabeculae, and ultimately with that of the capsule of the node. In its meshes, in the nodules and cords of lymphoid tissue, are closely packed lymph corpuscles. The node pulp is traversed by a dense plexus of capillary bloodvessels. The nodules or follicles in the cortical portion of the node frequently show, in their centers, areas where karyokinetic figures indicate a division of the lymph corpuscles. These areas are termed germ centers. The cells composing them have more abundant protoplasm than the peripheral cells.
The afferent vessels, as stated above, enter at all parts of the periphery of the node, and after branching and forming a dense plexus in the substance of the capsule, open into the lymph sinuses of the cortical part. In doing this they lose all their coats except their endothelial lining, which is continuous with a layer of similar cells lining the lymph paths. In like manner the efferent vessel commences from the lymph sinuses of the medullary portion. The stream of lymph carried to the node by the afferent vessels thus passes through the plexus in the capsule to the lymph paths of the cortical portion, where it is exposed to the action of the node pulp; flowing through these it enters the paths or sinuses of the medullary portion, and finally emerges from the hilus by means of the efferent vessel. The stream of lymph in its passage through the lymph sinuses is much retarded by the presence of the reticulum, hence morphological elements, either normal or morbid, are easily arrested and deposited in the sinuses. Many lymph corpuscles pass with the efferent lymph stream to join the general blood stream. The arteries of the node enter at the hilus, and either go at once to the node pulp, to break up into a capillary plexus, or else run along the trabeculae, partly to supply them and partly running across the lymph paths, to assist in forming the capillary plexus of the node pulp. This plexus traverses the lymphoid tissue, but does not enter into the lymph sinuses. From it the veins commence and emerge from the organ at the same place as that at which the arteries enter.
The lymphatic vessels are arranged into a superficial and a deep set. On the surface of the body the superficial lymphatic vessels are placed immediately beneath the integument, accompanying the superficial veins; they join the deep lymphatic vessels in certain situations by perforating the deep fascia. In the interior of the body they lie in the submucous areolar tissue, throughout the whole length of the digestive, respiratory, and genito-urinary tracts; and in the subserous tissue of the thoracic and abdominal walls. Plexiform networks of minute lymphatic vessels are found interspersed among the proper elements and bloodvessels of the several tissues; the vessels composing the net-work, as well as the meshes between them, are much larger than those of the capillary plexus. From these net-works small vessels emerge, which pass, either to a neighboring node, or to join some larger lymphatic trunk. The deep lymphatic vessels, fewer in number, but larger than the superficial, accompany the deep bloodvessels. Their mode of origin is probably similar to that of the superficial vessels. The lymphatic vessels of any part or organ exceed the veins in number, but in size they are much smaller. Their anastomoses also, especially those of the large trunks, are more frequent, and are effected by vessels equal in diameter to those which they connect, the continuous trunks retaining the same diameter.
Hemolymph nodes or nodes and hemal nodes which are so abundant in some mammals are probably not present in man.
Lymph.—Lymph, found only in the closed lymphatic vessels, is a transparent, colorless, or slightly yellow, watery fluid of specific gravity about 1.015; it closely resembles the blood plasma, but is more dilute. When it is examined under the microscope, leucocytes of the lymphocyte class are found floating in the transparent fluid; they are always increased in number after the passage of the lymph through lymphoid tissue, as in lymph nodes. Lymph should be distinguished from “tissue fluid” which is found outside the lymphatic vessels in the tissue spaces.
duct (ductus thoracicus) conveys
the greater part of the lymph and chyle into the blood. It is the common trunk
of all the lymphatic vessels of the body, excepting those on the right side of
the head, neck, and thorax, and right upper extremity, the right lung, right
side of the heart, and the convex surface of the liver. In the adult it varies
in length from 38 to
The cisterna chyli (receptaculum chyli) receives the two lumbar lymphatic trunks, right and left, and the intestinal lymphatic trunk. The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymph nodes. They receive the lymph from the lower limbs, from the walls and viscera of the pelvis, from the kidneys and suprarenal nodes and the deep lymphatics of the greater part of the abdominal wall. The intestinal trunk receives the lymph from the stomach and intestine, from the pancreas and spleen, and from the lower and front part of the liver.
Tributaries.—Opening into the commencement of the thoracic duct, on either side, is a descending trunk from the posterior intercostal lymph nodes of the lower six or seven intercostal spaces. In the thorax the duct is joined, on either side, by a trunk which drains the upper lumbar lymph nodes and pierces the crus of the diaphragm. It also receives the efferents from the posterior mediastinal lymph nodes and from the posterior intercostal lymph nodes of the upper six left spaces. In the neck it is joined by the left jugular and left subclavian trunks, and sometimes by the left bronchomediastinal trunk; the last-named, however, usually opens independently into the junction of the left subclavian and internal jugular veins.
lymphatic duct (ductus lymphaticus
Tributaries.—The right lymphatic duct receives the lymph from the right side of the head and neck through the right jugular trunk; from the right upper extremity through the right subclavian trunk; from the right side of the thorax, right lung, right side of the heart, and part of the convex surface of the liver, through the right bronchomediastinal trunk. These three collecting trunks frequently open separately in the angle of union of the two veins.
Lymphatic vessels and regional lymphatic nodes
The superficial and deep vessels are distinguished in lower limb. The superficial vessels are situated over superficial fascia and deep vessels positioned closely to deep blood vessels. Popliteal nodes and inguinal nodes are distinguished in lower limb. Last one subdivide into deep inguinal nodes and superficial inguinal nodes. Superficial inguinal nodes dispose along inguinal ligament and lie on superficial sheet of fascia lata femoris. Their efferent vessels pass to external iliac nodes, which accompany same name artery.
The superficial vessels of lower limb formed from capillary skin networks and subcutaneous cellular tissue and form medial, lateral and posterior vessel groups.
Medial group of superficial vessels formed in skin of I, II and III fingers, medial part of foot and medial surface of shin. These vessels run along vena saphena magna and empty into superficial inguinal nodes.
Lateral group of superficial vessels of lower limb formed laterally in area of fingers in dorsal foot surface and lateral surface of shin. These vessels beneath knee join to medial group.
Posterior group of superficial vessels of lower limb starts in skin of heel and plantar surface of lateral foot margin, passes along the vena saphaena parva and runs into popliteal lymphatic nodes.
Deep vessels of lower limb drainage muscles, joints, synovial sheaths, bones, nerves, accompany deep arteries and veins and empty into deep inguinal nodes.
In pelvic area differ the visceral and parietal lymphatic nodes.
The visceral lymphatic nodes dispose near pelvic organs and they are: paravesical, prevesical and retrovesical nodes, lateral vesical nodes, parauterine nodes, paravaginal nodes and pararectal or anîrectal nodes. The efferent vessels from these nodes pass into iliac nodes, mainly to common iliac nodes and to retroaortic nodes. Lymph flows from ovaries into lumbar nodes.
The parietal lymphatic nodes disposed along the course of big vessels common iliac nodes; internal iliac nodes, which unite gluteal and sacral nodes. External iliac nodes join obturator nodes. The efferent vessels from these nodes pass first into common iliac nodes, then into retroaortic nodes, and from them - into lumbar lymphatic nodes.
In abdominal cavity, as and in pelvis, lymphatic nodes may be divided into two sets, parietal and visceral.
The Visceral lymphatic nodes dispose along the course of big vessels come away from abdominal aorta, they receive lymph from all internal abdominal organs: coeliac nodes, right/left gastric nodes, lymphatic unnulus of cardia, right/left gastroepiploic nodes, pyloric nodes, pancreatic nodes, splenic nodes, pancreatoduodenal nodes, hepatic nodes, superior mesenteric nodes and inferior mesenteric nodes. The lymphatic vessels of the small intestine receive the special designation of lacteals or chyliferous vessels; they differ in no respect from the lymphatic vessels generally excepting that during the process of digestion they contain a milk-white fluid, the chyle. The lymphatic vessels and nodes of the small intestine positioned in mesentery and empty into intestinal trunk. The vessels take away lymph from these nodes, pass to lumbar nodes. Efferent vessels of last form the lumbar trunks, which flowing together form a thoracic duct.
The parietal lymphatic nodes disposed around aortae and inferior vene cava - right/left and intermidiate lumbar nodes, lateral aortic nodes, preaortic nodes, retroaortic nodes, lateral caval nodes, precaval nodes, retrocaval nodes, inferior phrenic nodes and inferior epigastric nodes.
Lymphatic vessels of superior half of abdominal wall pass upward to the axillar lymphatic nodes. The vessels of inferior half of abdominal wall pass downward to inguinal lymphatic nodes.
Lymphatic nodes of the thorax may be divided into two sets, parietal and visceral. There distinguish the following parietal nodes of thorax:
1. Parasternal nodes collect lymph from pericardium, pleura, anterior thoracic wall, diaphragmatic surface of liver, mammary gland. The vessels from these nodes carry lymph into right and left venous angles.
2. Intercostal nodes empty lymph into thoracic duct, and from superior nodes - into deep lateral jugular lymphatic nodes.
3. Superior phrenic nodes carry lymph into parasternal nodes, nodes inferior tracheobronchic and into bronchîpulmonary nodes.
4. Prepericardial nodes transport lymph into parasternal nodes, nodes inferior tracheobronchic and into bronchîpulmonary nodes.
5. Prevertebral nodes are disposed between backbone and esophagus.
6. Paramammary nodes are disposed laterally from breasts and drain them.
The visceral lymph nodes include the following groups:
1. paraesophageal nodes
2. paratracheal nodes
3. tracheobronchic nodes
4. bronchîpulmonary nodes
All foregoing visceral nodes of thorax according old anatomic nomenclature, belong to anterior and, especially, posterior mediastinal lymphatic nodes (nodi lymphatici mediastinales anteriores et posteriores). Left half of thoracic cavity is drained to thoracic duct, right half - into right lymphatic duct.
Lymph from head and neck gathers into right and left jugular lymphatic trunks, which pass on each side near internal jugular vein and fall: right - into right lymphatic duct or into right venous angle and left - into thoracic duct or immediately into left venous angle. Before duct lymph passes through regional lymphatic nodes.
Lymph from head runs into nodes positioned on boundary between head and neck. They include the following: 1) occipital nodes, 2) mastoid nodes, 3) superficial parotid nodes, 4) deep parotid nodes, 5) submandibular nodes, 6) facial nodes, 7) submental. Efferent vessels from these nodes extend in deep cervical nodes.
There are two groups of lymphatic nodes on neck - anterior cervical nodes and lateral cervical nodes, which subdivide into superficial and deep. Anterior deep lymphatic nodes: prelaryngeal nodes, thyroid nodes, pretracheal nodes, paratracheal nodes. The superficial lateral nodes lie along external jugular vein, and deep - along internal jugular vein.
Lymphatic nodes of upper limb may be divided into two sets, superficial and deep.
The superficial vessels and nodes of upper limb pass along the course of vena basilica and vena cephalica and compose lateral, medial and middle groups. Lateral group of superficial vessels carries lymph from skin of I-²²² fingers, lateral forearm surface and arm to axillar lymphatic nodes. Medial group of superficial vessels carries lymph from IV-V fingers, hand, medial forearm side and brachium to cubital and axillar lymphatic nodes. Middle group carries lymph from palmar forearm surface to cubital fossa and here part of vessels joins to lateral grand, and part to medial group. The superficial lymphatic nodes accompany the superficial hand veins. They collect lymph from skin and subcutaneous tissue. From them lymph passes to cubital nodes and axillar nodes.
Deep vessels and nodes of upper limb accompany the deep big vessels and carry lymph into deep nodes and superficial nodes, and from here - into cubital nodes and axillar lymphatic nodes. Axillar nodes receive the vessels from upper limb, thoracic wall, and mammary gland. The efferent vessels from axillar nodes form a subclavian trunk (left and right).
Lymphatic annulus of pharynx belongs to secondary lymphatic organs and consists of lingual tonsil, palatine tonsil, pharyngeal tonsil and tubarius tonsil. They have tonsillar cryptae and tonsillar fossulae and lymphatic nodules. These tonsils are described in part “pharynx". Tonsils are agglomerations of lymphoid tissue, which is disposed in area of entrance to pharynx and nasopharynx. They are placed around initial portions of high respiratory and digestive paths (lymphoepithelial ring of Pyrohov-Valdeyer).
The Lymphatic follicles of gastrointestinal tract are agglomeration lymphoid tissue in mucous membrane of the stomach (the gastric lymphatic follicles), small intestine (solitary lymphatic follicles and aggregate lymphatic follicles – Payer patches), large intestine (solitary lymphatic follicles and aggregate lymphatic follicles of vermiform processes). The largest amount of Payer patches is situated in distal portion of iliac bowel. Ò-lymphocytes migrate freely from lymphatic follicles through epithelium of mucous membrane into intestinal shaft of light.
The SPLEEN belongs to secondary lymphatic organs and is a big lymphatic node. Spleen is disposed in left hypochondriac on the level of 9-11 ribs. Spleen has inferior margin and superior margin, anterior extremity and posterior extremity. It has a diaphragmatic surface (superior) and visceral surface (inferior). To the last adjoin stomach (facies gastrica), left kidney with suprarenal gland (facies renalis), left colic flexure (facies colica) and tail of pancreas (facies pancreatica). Place on visceral surface, where vessels and nerves enter and leave, is called as splenic hilus. Spleen is covered by peritoneum from all sides (lies intraperitoneally).
Spleen is covered by fibrous capsule, from which numerous small fibrous bands, trabeculæ are given off in all directions into parenchyma, these uniting, and constitute the framework of the spleen. Parenchyma consists of splenic pulp, which has a white pulp and red pulp and its structure described in detail in histology course.
ORGANS of IMMUNE SYSTEM and HAEMOPOESIS
Immune system unites organs and tissues, which provide defense from genetically foreign cells or matters, that got from out or are generated inside the organism, providing constancy of internal organism environment. Organs of immune system may be divided into central and peripheral part.
To central organs of immune system belong thymus gland and red marrow.
To peripheral organs of immune system unite organs are not enveloped in capsule (tonsils, lymphoid follicles, that are situated in walls of hollow organs of digestive and respiratory systems and lymphocytes, which are situated in blood, lymph, connective and epithelial tissue) and capsulated organs (lymphatic nodes and spleen).
Thymus is placed in front part of superior mediastinum and consists of lobes, more frequent two. Outside this gland is tunicate by fibrous capsule that gives off septa, which split up lobes on lobules. They comprise reticular cells with lymphocytes between them (called as ‘thymocytes’). The lobules of gland have a cortex and medulla thymi. Can be accessories lobules of thymus. Basic function of thymus maturation and supporting of effector cells (killer) and regulatory cells (helper and supressor) Ò-lymphocytes populations. Also thymus takes part into regulation of neuro-muscular transmission, phosphoric-calcium metabolism, carbohydrate and peptide metabolism, interaction with other endocrine glands (that's why one can be consider thymus gland as a endocrine organ).
Red marrow is sole haemopoetic organ in adult and central organ of immune system. Stem cells are generated in it, they are like lymphocytes because their morphology and during cell-fission give beginning to all formal blood elements, also including cells providing immunity - to leukocytes and lymphocytes. Red marrow in adult is situated in cells of spongy matter of flat and short bones, in epiphysis of long tubular bones. Yellow marrow is situated in diaphysis of long tubular bones. Largest amount of red marrow is situated into epiphysis of femoral and tibiae bones.