central and peripheral organ of Hematopoiesis – Structure & function

The central organs of hematopoiesis and immune defense in humans include the red bone marrow and thymus. In the red bone marrow, erythrocytes, platelets, granulocytes, and lymphocyte precursors are formed. The thymus is the central organ of lymphopoiesis.


Central organs of hematopoiesis –

A – red bone marrow (1 – frosty hemocapillary; 2 – reticular tissue; 3 – hematopoietic islets);

B – thymus – thymus gland (1 – capsule; 2 – lobules; 3 – layered epithelial bodies in the medulla).


Red Bone Marrow – (organ of Hematopoiesis)


a) The cells of each direction of myelopoiesis are located in the red bone marrow by islets.
b) The islets are dominated by cells of the V class of hematopoiesis.


1. Erythropoietic islet

a)        a) class IV cells – erythroblasts,

b)        cells of class V –

i.          proerythro -blasts

1.         the largest in size among the cells of the islet,

2.        have a basophilic nucleus

ii.        basophilic erythroblasts

1.        slightly smaller in size;

2.        both the nucleus and the cytoplasm is basophilic

iii.      Polychromatorsphilous erythroblasts

1.        grayish cytoplasm

iv.       oxyphilic erythroblasts 

1.        oxyphilic cytoplasm,

2.        the cell size is smaller, the nucleus is still contained

c)        Class VI cells – reticulocytes and erythrocytes

2. Granulocytopoietic islets.

a)        These islands can be of 3 types:

i.          neutrophilic 

ii.        Eosinophilic

iii.      Basophilic

b)        They contain

i.          class IV cells – myeloblasts (usually not identified),

ii.        cells of class V –

1.        promyelocytes (have primary granularity),

2.        myelocytes (secondary specific granularity; round nucleus);

3.        metamyelocytes, or young granulocytes (the nucleus is bean-shaped),

4.        stab granulocytes

iii.      class VI cells – segmented granulocytes

3. Cells of the platelet series

a)        This includes

i.          megakaryoblasts,

ii.        Promegakaryocytes

iii.      megakaryocytes.

b)        Usually these cells are associated with blood capillaries.

c)        Near one of the capillaries megakaryocyte are present – a large multinucleated cell.

d)        Its cytoplasm, in some part of it usually penetrates into the lumen of the capillary

4. Cells that look like small lymphocytes 

a)        Some of these cells are –  poorly differentiated cells of classes I-III.

b)        Usually, they are located between the islets

c)        According to the above (clause, in those cells that are the precursors of lymphocytes, a unique process of the formation of new genes – immunoglobulin genes – takes place.

d)        Other cells similar in morphology – more mature cells of the monocytic and B-lymphocytic series.


Parenchyma presented hotbeds myeloid hematopoiesis, which located at weaves reticular tissue in the form of three structural cooperations.



Thymus – (organ of Hematopoiesis)

Thymus is the central organ of lymph and immunopoiesis. Anatomically represented by two lobes, located in the anterior mediastinum.

Basic functions of the thymus: –

  • In embryogenesis determines the formation of the immune systems.
  • The postembryonic and postnatal period is the center of antigen-independent and antigen – dependent T-lymphopoiesis, as well as a regulator of B-lymphopoiesis in peripheral lymphoid organs.
  • Endocrine function – secretion of local and distant hormones that regulate lymphopoiesis, as well as body growth and sexual maturation


The structure of the thymus –

Parenchyma represented segments, separated from each other thin layers of connective tissue with blood vessels and nerve fibers (Fig. 1) Structural basis lobules are epithelio reticulocytes – process cells, which connect with each other form a multidimensional network( syncytium ). In this network, cells are located and develop lymphoid series, which are often called thymocytes.

Each lobule on its periphery has a dark cortical


substance and in the center – light medulla. They are functionally independent of each other:

• have different pathways of intra-organ blood supply;

• perform differently functions in the T-lymphoimmunopoiesis system.



Peripheral lymphoid organs – (organ of Hematopoiesis)

They have antigen-dependent proliferation and differentiation of T and B cells of lymphocytic rows hematogenous diferon, which came with blood flow from the medulla of the thymus, or from tissues of other organs. It committed lymphocytes, i.e. they had their first meeting with the antigen.


– The parenchyma of these organs is represented by lymphoid tissue (blood cells of the lymphocytic series in the reticular tissue), which is assembled in the form of structural complexes:

• lymphoid nodules (follicles) – typical for all peripheral lymphoid organs


diffuse distribution of lymphoid cells – characteristic for all peripheral lymphoid organs;

  • lymphoid cords – characteristic of lymph nodes
  • periarterial lymphoid sheaths (cases) – characteristic of the spleen;


These complexes are divided into zones:

    a. Thymus dependent (controlled by thymosin);

    b . Thymus-independent




onal parenchymal organ. From the outside, it is covered with a connective tissue capsule, which adjoins the mesothelium. The capsule contains smooth myocytes. Depart from the capsule of the trabeculae RVNST. In the trabeculae also found bundles of smooth muscle cells. Capsule and trabeculae form a support-contractile apparatus spleen is 7% of its volume. All the space between the capsule and trabeculae filled the reticular tissue. Reticular tissue, trabeculae, and capsule form the stroma of the spleen. The collection of lymphoid cells is its parenchyma.


The white pulp – a collection of lymphoid follicles (nodules) that lie around the central arteries. The white pulp is one-fifth of the spleen. Lymphoid nodules of the spleen differ in structure from the lymph node follicles as contain both T-and B-band (recall that in the lymph node follicles are a B-band). Each follicle has four zones:

  1. Jet Center (Center of reproduction).
  2. Mantle zone – a crown of small B-lymphocytes memory.
  3. Marginal zone.
  4. Periarterial zone or periarterial lymphoid coupling (PALM) – a zone around the central arteries.



The ratio of white and red pulp may be different. In connection with this release is two types of spleens.

a) The type of immunity is characterized by a pronounced development of the white pulp;
b) the metabolic type, which is much dominated by red pulp.


Functions: –

  1. Hemopoietic
  2. Barrier – protective – phagocytosis
  3. Deposition
  4. The exchange function
  5. Hemolytic function
  6. Endocrine function


Lymph nodes

In peripheral organs immunogenesis there is a meeting of immune cells with antigens. After that include immune responses, which are based on the differentiation of antigen lymphocytes. The result is the effector cells that inactivate the antigens. If the destruction of the antigen is in the reactions of cellular immunity, the effector cells are cytotoxic T-killer cells. In the humoral immune response effector, cells are plasma cells (plasma cells), forming antibodies.

Lymph nodes (glands) are located along the limfososudov and retain antigens trapped in the lymph, purifying it.


Function: –

  1. Hemopoietic
  2. Barrier – protective – phagocytosis
  3. Drainage Function
  4. The exchange function
  5. Function Deposit
  6. Endocrine function


The structure of the lymph nodes –

  • number of lymph nodes of approximately 1,000, 1% of body mass
  • Dimensions are on average 0.5-1 cm
  • round kidney-shaped
  • regionally in relation to the bodies in groups
  • On the convex the surface of the lymph nod


Lymph nodes are the zonal parenchymal organs. They are the following structural and functional components.

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