Lymphatic Organs and Tissue: Lymph nodes, Spleen, Thymus, Tonsil's- Peyer's Patches

Lymph Nodes

The lymph nodes are bean-shaped organs that are dispersed widely along the lymphatic system. Both superficial and deep, they are dispersed throughout the body and typically occur in groups. These nodes serve as a conduit for the movement of lymph to the subclavian veins. Numerous afferent lymph vessels carry lymph into the node, whereas only one or two efferent lymph vessels carry lymph out. Macrophages pahagocytize bacteria and other foreign substances as lymph moves through a lymph node.

Lymph nodes are enclosed by a capsule of tight connective tissue and range in size from 0.04 to 2.5 cm (0.04 to 1 inches). They are mostly concentrated in the neck, axillae, groin, thoracic region, mediastinum, and mesenteric of the gastro intestinal tract, with an average human body containing 600–700 of them.

Location of the Lymph Nodes:

There are numerous groups of lymph nodes distributed throughout the body's lymphatic veins, including:

• Cervical lymph nodes:
  • Behind and below the ear along the inferior margin of the mandible and down the side of the neck.
• Axillary lymph nodes:
  • From the arm, through armpit to the thoracic wall, breast and superior abdominal wall.
• Thoracic lymph nodes:
  • Along the trachea and bronchi.
• Abdominal lymph nodes:
  • Along abdominal aorta and mesenteric anterior.
• Pelvic lymph nodes:
  • Along the iliac arteries and vein.
• Inguinal lymph nodes:
  • In the groin.

Structure of the Lymph Nodes:

The size of lymph nodes varies. The smallest are roughly the size of an almond, and the largest are smaller than a pinhead. They feature a fibrous outer capsule that dips into the substance of the node to generate partitions or trabeculae. Reticular and lymphatic tissue that is rich in lymphocytes and macropages makes up the bulk of the node. One to a few efferent lymph vessels carry lymph away from the lymph node, while four or more afferent lymph vessels may enter the lymph node. The node filters the lymph as it moves through it. An artery enters each node at the concave surface known as the hilum, and a vein and efferent arteries exit there.

• Capsule:
  • Each lymph node has a tight connective tissue capsule covering it that extends inside the node as trabeculae (plural: trabeculum). The subcapsular or cortical sinus, a region that absorbs lymph from afferent lymphatic channels, is located just beneath the capsule.
• Stroma:
  • Framework of the lymph node, is made up of a network of reticular fibers and fibroblasts that is located inside the capsule. The functional cells (lymphocytes and macrophages) or parenchymal (the essential and characteristic tissue of an organ as differentiated from its supporting framework) of the lymph nodes are housed inside this framework. The cortex and medulla of lymph nodes are the two areas of specialization.
  • Cortex:
    • Lymphocytes are tightly clustered into masses called lymphatic nodules in the outer cortex. A nodule's periphery is made up of macrophages and T cell lymphocytes. The germinal core, which is the nodule's lighter central area when an immunological response occurs, is where B cell lymphocytes proliferate into cells that release antibodies (plasma cells).
  • Medulla:
    • Medullary cords are strands of tightly packed lymphocytes (B and T lymphocytes) that make up the medulla, the inner part of a lymph node.

Functions of the Lymph Nodes:

By acting as filters, lymph nodes remove toxins and bacteria from the lymph. These are the roles of the lymph nodes:

• The lymph is filtered, or the water and electrolytes are taken out, as it moves through the lymph nodes. However, the lymph retains the proteins and lipids.
• The macrophages in lymph nodes eliminate bacteria and other harmful chemicals. Be a result, lymph nodes are referred to as defense barriers.

Accessory Organs of Lymphatic System:

1. Thymus gland:

The thymus is a lymphoid organ that rises upward from the upper section of the mediastinum of the thorax, behind the sternum. It has two pyramid-shaped lobes, weighs 10-15 gram at birth, increases in size until puberty, and reaches its maximum weight of 30–40 gram at that time. It starts to contract around puberty, and by adulthood, it is quite little. As a result, it progressively gets back to where it was at birth.

Trabeculae extend into the substance of the thymus from its fibrous capsule, dividing each lobe into two lobes. Each lobule has a medulla and cortex that are home to lymphocytes. The thymus is an endocrine and lymphatic organ. It secrets hormones, thymopoietin and thymosin, which stimulate the development and activity of T-lymphocytes and make them capable of fighting pathogens.

After then, T cells depart from the thymus and enter the circulation. While others circulate in the bloodstream, some move into lymphoid tissues. Although it is greatest in childhood, the generation of T lymphocytes likely continues throughout life as a resident population of thymic stem cells.

Thymosin promotes the development of lymphoid tissue, including the thymus. Adolescence is when the gland first starts to shrink, and as people age, their ability to respond to antigens with T lymphocytes becomes less efficient.

Organs Associated with the Thymus:

• Anteriorly: Sternum and upper four costal cartilages.
• Posteriorly: Aortic arch and its branches, brachiocephalic veins, trachea.
• Laterally: Lungs.
• Superiorly: Structures in the root of the neck.
• Inferiorly: Heart.

Structure of the Thymus gland:

• The two lobes of the thymus are connected by areolar tissue. The lobes are encased in a fibrous capsule that extends into their substance and divides them into lobules, each of which is made up of an irregularly branched framework of lymphocytes and epithelial cells.

Functions of the Thymus gland:

• T-lymphocyte development is promoted by the thymus.
• T cells are activated by the thymus and are used to discriminate between self and foreign tissue.
• Additionally, it enables each T-lymphocyte to respond only to one particular antigen out of the millions it will come into contact with.

2. Spleen:

The largest lymphatic organ is the spleen. It is located in the left hypochondriac region of the abdomen, slightly below the diaphragm and above the stomach, and is dark purple in color. It is 2.5 cm thick and 12 cm wide. It is about 200 grams in weight.

Organs Associated with the Spleen:

• Superiorly and posteriorly: Diaphragm.
• Interiorly: Fundus of stomach.
• Inferiorly: Left colic flexure of the large infesting.
• Medially: Pancreases and left kidney.
• Laterally: Separated from the 9th, 10th, 11th ribs and the intercostals muscles by the diaphgram.

The spleen has a somewhat oval shape with a medial hilum through which the spleenic artery and vein enter and exit. There are two different types of tissue that make up the spleen's parenchyma.

• White Pulp:
  • The white pulp of a lymphatic tissue is primarily made up of lymphocytes and macrophages clustered around splenic artery branches.
• Red Pulp:
  • Blood sinuses that are loaded with RBCs and lymphocytes make up the red pulp. The interior structure of the spleen resembles that of the lymph nodes.

Functions of the Spleen

The spleen has multiple functions:

• Haemopoiesis:
  • The spleen is a crucial organ in hemopoiesis. It produces neutrophils, RBC, and platelets. In red pulp, platelets are created. Blood cells are produced both during pregnancy and as an adult.
• Storage of blood:
  • Adult spleens also serve as blood reservoirs for storing blood. Because of its highly permeable capillaries, RBC can concentrate in the sinuses of the red pulp and exit the blood stream in the event of a significant hemorrhage.
• Erythrocyte destruction:
  • The adult spleen also serves as a "erythrocyte graveyard." Old, frail, and aberrant erythrocytes are primarily destroyed in the spleen, and the breakdown byproducts, such as bilirubin and iron, are then delivered into the liver via the splenic and portal vein. Other cellular material eg. leukocytes, platelets and bacteria are phagocytized in the spleen.
• Immune response:
  • The spleen removes lymph nodes from the circulation. White pulp lymphocytes and macrophages serve to generate protective immune responses by identifying foreign antigens in the blood and lymph.
  • The blood platelets are stored in the spleen.

The function of the spleen is covered by other organs, hence it is not regarded as a crucial organ. Old and dysfunctional red blood cells (RBCs) and platelets are removed from circulation by the liver and red bone marrow. Like the liver, many lymph nodes and nodules will phagocytize infections and create antibodies by activating lymphocytes and plasma cells.

3. Tonsils:

At the pharynx's opening are patches of lymphatic tissue called tonsils. Three sets of tonsils are present.

• Two lingual tonsils are located at the tongue's base.
• Two palatine tonsils are located near the back of the mouth cavity.
• A single medial pharyngeal tonsil on the pharynx's posterior wall, known as the adenoid tonsil.

The epithelium that covers each tonsil creates lymphatic nodules and deep pits known as tonsil crypts. Pathogens that are consumed or breathed are captured and eliminated by lymphocytes. The largest and most frequently infected tonsils are the palatine ones. Adenoids are pharyngeal tonsils that have hypertrophied.

Functions of the Tonsils:

• The tonsils phagocytize foreign material from the lymph much like any other lymph node would.
• They gather and eliminate germs that are consumed or inhaled and enter the throat.