Lymphatic (Immune) System!

• The immune system is classified into the lymph vessels, which include lymph capillaries, principal lymph vessels, and main lymph vessels such as the ductus thoracicus and ductus lymphaticus dexter.
• The central organs of the immune system are the bone marrow and the thymus.
• Lymph sinuses are present in the lymph node.
• The lymph node is a small, bean-shaped body situated in groups (about 150 groups of regional lymph nodes).
• The secondary lymph follicles have a central, light zone (activated B-lymphocytes, macrophages, follicular dendrite APCs), called reactive centre.
• In the T-region, there is a process of transformation of T-lymphocytes under antigen influences in active cellular subclasses.
• Peripheral organs associated with the mucous membrane lymph tissue (MALT) include lymph nodes, spleen and associated tissues.
• The connective tissue stroma of the organ is made by reticular type of connective tissue (reticular cells, classical macrofages, antigen presenting cells - APCs).
• APCs are dendrite (interdigitating) cells of the paracortical zone of the lymph node.
• Follicular dendrite APCs are in the reactive centre of the lymph follicle.
• Stromal macrophages of the lymph node are immunoreactive for acid phosphatase.
• The lymph node has three parts: cortical part, cortex; peripheral part, under the capsule; and inner part, medulla.
• Afferent lymph vessels enter the lymph node in the parenchyma, forming lymph sinuses.
• Efferent lymph vessels collect together and leave the lymph node through the hilus.
• Lymphocytes enter and leave the lymph node parenchyma through high endothelial venules (HEVs) of the paracortical zone, T-region (lymphocyte homing receptors).
• The cortical part of the lymph node consists of lymph follicles with a reactive centre.
• The lymph follicles in the cortex are spherical bodies, with primary and secondary (activated) follicles.
• The lymph node has a fibrous capsule, with connective tissue slips (trabeculae) extending from the capsule into the organ stroma.
• B-lymphocytes circulate in the lymph node parenchyma.
• The spleen has a bean-shaped structure with two surfaces: upper (facies diaphragmatica) and lower (facies visceralis), two edges (margo superior, serrated, serratus) and two poles (extremitas anterior, extremitas posterior).
• On the visceral surface of the spleen, there is a depression known as the hilum (where blood vessels and nerves enter and leave).
• The spleen has a capsule outside (fibrous capsule) and from the capsule extend loose connective tissue slips (trabeculae, rich of smooth muscle cells).
• The true stroma of the spleen is from reticular type of connective tissue.
• The blood sinuses in the red pulp of the spleen are large in size, have interrupted basal lamina, and do not contain pericytes.
• In the wall of the blood sinuses in the red pulp of the spleen, there are some stromal cells: macrofages, reticular cells and reticular fibers.
• The spleen is situated in the upper left part of the abdomen, known as the region hypohondriaca sinistra.
• The parenchyma of the spleen has two parts: white pulp (pulpa lienis alba) and red pulp (pulpa lienis rubra).
• The spleen is entirely covered by peritoneum, known as the saccus caecus lienis.
• The blood supply of the spleen comes from the aorta (a.lienalis, branch of the truncus coeliacus), aa.trabeculares, aa.pulpares, a.centralis, vv.trabeculares, v.lienalis, v.portae.
• The white pulp of the spleen consists of bodies of Malpighii, each body of Malpighii consists of lymph follicle and central arteriole (a centralis, branch of a lienalis).
• The spleen has impressions on the visceral surface from the neighbor organs: left kidney and adrenal gland, stomach, pancreas and flexura coli sinistra.
• The functions of the spleen include defense and blood reservoir.
• Bone marrow consists of elements such as reticular fibers, reticular cells, tissue macrophages, secretory macrophages (cytokines and growth factors like IL-1, GM-CSF, GCSF), and extracellular matrix rich in GAGs.
• The red pulp of the spleen consists of blood sinuses and B-ly organized in irregular clusters.
• The spleen is a peripheral immune organ and the biggest immune organ.
• The thymus (adult) has a different microscopic structure from the child thymus.
• The stroma of bone marrow is without a capsule and is from reticulat type of connective tissue.
• Bone marrow takes about 4,5% of the body mass by the adult.
• The thymus has elements of the defense barrier: endothelial cells of the blood capillary, basal lamina of the blood capillary, basal lamina of the epithelial like cells of the stroma, epithelial like cells of the stroma.
• Gut associated lymphoid tissue (GALT) is very well developed in the digestive system.