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Main page | Structure | Departments | Department of Histology and Embryology | Materials for students | Modul 2 | THYMUS. RED BONE MARROW.

THYMUS. RED BONE MARROW.
 
THYMUS.
  1. Thymus is CENTRAL hemopoietic (lymphoid) organ, because it fulfils function of antigen-INDEPENDENT proliferation and differentiation of T-lymphocytes (shortly- function is T-lymphocytopoiesis).
  2. Structure on the cross section:
Connective tissue capsule, connective tissue septa extend from capsule and divide organ on incomplete lobules. Each lobule contains stroma and parenchyma. Stroma is epithelium. One cell of stroma is epithelial reticular cell (ERC). ERC has cytoplasmic processes (star-shaped). ERCs, anastomosins with each other, form 3D-mashwork. Inside loops of this mashwork numerous T-lymphocytes locate.
All developing lymphocytes is lymphoid tissue.
  1. Lymphoid tissue is parenchyma of  thymus. T-lymphocytes form cortex and medulla in the lobule. Central part of medulla contains concentrically arranged ERCs, forming thymic corpuscles (Hassal´s corpuscles).
                    Antigen-INDEPENDENT proliferation and differentiation of T-lymphocytes happens in lobule cortex.
  1. Thymus undergoes involution (atrophy). If involution happens slowly, during years after puberty, it is age involution. If involution happens abnormally ratidly, during days, it is accidental involution. Essence of both is replacement of lymphoid tissue parenchime by adipose tissue (T-cells irreversible die by apoptosis). Glucocorticoid hormones and chronic stress cause accidental involution.
  2. ERCs arise from endoderm of 3rd-4th pharyngeal pouches. T-lymphocytes arise from mesenchyme.
 
RED BONE MARROW (RBM).
RBM is CENTRAL hemopoietic (lymphoid) organ, because it fulfils function of antigen-INDEPENDENT proliferation and differentiation of B- lymphocytes
1.RBM is composed of 3 compartments:
             A) stromal compartment. It is reticular tissue. Tthis tissue forms 3D-mashwork. Inside loops of this mashwork another 2 compartments locate.
Reticular cells of stroma secrete factors, stimulating hemopoiesis. It are: interleukins (ILs) and colony stimulating factors (CSFs).
             B) hemopoietic (parenchymal) compartment. It is myeloid tissue. Myeloid tissue is composed of 5 types developing hemopoietic cells :erythrocytes, monocytes, platelets, granulocytes, B- lymphocytes. Hemopoietic cells form associations- hemopoietic islets. Macrophage of RBM (nurse cell) has elongated processes. Erythroblasts attached to it. This is erythroblastic islet.
             C) vascular compartment. It presented by sinusoidal capillaries. Megakaryocytes protrude cytoplasmic processes into capillary lumen through clefts in endothelium. It is islet of thrombocytopoiesis.
 
Red bone marrow fulfils 2 main functions:
  1. It is UNIVERSAL hemopoietic organ, because releases into peripheral blood 4 types mature blood cells: erythrocytes, monocytes, platelets, granulocytes, and naïve B- lymphocytes.
  2. It is CENTRAL lymphoid organ, because it fulfils function of antigen- INDEPENDENT proliferation and differentiation of B-lymphocytes.
Куратор темы – доцент В.В. Бондаренко.
 
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