Hematopoietic Tissue: Characteristics, Histology, Functions

The hematopoietic tissue is a tissue where the formation of blood cells takes place. Considered part of the vascular or connective tissue of different groups of animals, it has cells with short- or long-term regenerative capacities and committed multipotent, oligopotent and unipotent progenitor cells.

With the advancement of the microscope in the 19th century, it was possible to observe the different blood cells, their proliferation and differentiation. From then on it was known that the site of blood formation was the bone marrow.

Hematopoietic tissue. Taken from http://emecolombia.foroactivo.com/t2347-tejido-hematopoyetico-y-sangre-luisa-maria-contreras-sarmiento-grupo-b

Many hypotheses were put forward to explain the formation of blood cells, but it was the German pathologist Franz Ernst Christian Neumann (1834-1918) who proposed the pioneering theory of the stem cell. 
This theory suggests that one cell could be at the origin of all blood cell lineages.

Another prominent scientist in the area was the Russian-American Alexander A. Maximow (1874-1928). Maximow proposed the theory of a common cell for the complete hematic system or hematopoiesis. The modern concept of origin and differentiation of blood cells is based on this Maximow theory.

Article index

  • one

    Hematopoiesis

    • 1.1

      In general

    • 1.2

      In humans

  • two

    Histology

  • 3

    Types of hematopoietic tissues

    • 3.1

      Myeloid tissue

    • 3.2

      Lymphoid tissue

  • 4

    Features

    • 4.1

      Myeloid tissue

    • 4.2

      Lymphoid tissue

  • 5

    Processes

    • 5.1

      Myelopoiesis

    • 5.2

      Lymphopoiesis

  • 6

    References

Hematopoiesis

In general

It is known as the process by which all mature blood cells are produced. These cells have a limited life span, from a few hours in the case of white blood cells to 4 months in the case of red blood cells, which means that they must be constantly replaced.

The hematopoietic process is responsible for balancing the body’s daily needs for blood cell production. 
In vertebrate organisms, most of this process occurs in the bone marrow.

It derives from a limited number of hematopoietic stem cells that can generate cells of the same layer or of embryonic origin. They can also come from blood stem cells that can differentiate into multiple blood cell types (multipotent cells) and are capable of extensive self-renewal.

In humans

In humans, the places where hematopoiesis occurs change during development. In embryos it is carried out mainly in the yolk sac. During the fetal stage the process moves to the liver, spleen, lymphatic tissue and later to the red bone marrow.

Later, after birth, the production of blood cells is transferred to the bone marrow of the trabecular bone and the medullary cavity of the long bones.

Finally, in adults, it occurs in the bones of the skull, pelvis, vertebrae, sternum, and the areas near the epiphysis of the femur and humerus. Hematopoiesis in adults can restart in the liver and spleen under certain circumstances.

Structure of a long bone. Taken and edited from
http://inworldztech.com/anatom%EDa-%F3sea-femoral

Characteristics of hematopoietic tissue

Hematopoietic tissue comes from the mesoderm, constitutes 4 to 6% of body weight and is a soft, densely cellular tissue. It is made up of the precursors of blood cells, macrophages, fat cells, reticular cells, and reticular fibers.

The cells that make it up are responsible for the proper functioning of the body through oxygenation, elimination of biological waste, transport of cells and components of the immune system.

Histology

The connective or connective tissue is made up of cells and extracellular matrix, which comprises the fundamental substance and the fibers immersed in it. This tissue is known to have its origin in the mesoderm, from which the mesenchyme is formed.

On the other hand, in adult organisms the connective tissue is classified into two varieties: the connective tissue itself and the specialized connective tissue that corresponds to adipose, cartilage, bone, lymphoid tissues and blood (to which hematopoietic tissue belongs).

Types of hematopoietic tissues

Hematopoietic tissue is divided into 2 types of tissues:

Myeloid tissue

It is a type of hematopoietic tissue related to the production of erythrocytes (erythropoiesis), granulated leukocytes and megakaryocytes. Fragments of megakaryocytes form platelets (thrombocytes).

The myeloid tissue is located at the level of the medullary canal and the trabecular bone spaces of the long bones in young animals. In adult animals it is limited only to the level of the epiphyses of the long bones.

During the embryonic stage this tissue is found in the liver and spleen, and can persist even during the first weeks of life. In humans, myeloid tissue is usually limited to the bone marrow of the ribs, sternum, vertebrae, and epiphyses of long bones in the body.

Lymphoid tissue

Lymphoid tissue is also a hematopoietic tissue. This tissue exists in well-defined organs that are covered with connective tissue. It is called encapsulated lymphatic tissue and the organs that present it are the lymph nodes, spleen and thymus.

There is also a non-encapsulated lymphatic tissue and it is forming a defense barrier in the body; in organs exposed to environmental contamination such as the submucosa of the intestine, respiratory tract, urinary tract and genitalia.

Features

Myeloid tissue

Myeloid tissue is responsible for making red blood cells (blood cells that contain hemoglobin and carry oxygen in the body), platelets or thrombocytes, and white blood cells called neutrophils, eosinophils, and basophils (granulocytes).

Lymphoid tissue

The functions of this fabric depend on whether it is non-encapsulated or encapsulated fabric. The first fulfills the function of forming defense barriers against possible pollutants in the environment (see types of tissue, lymphoid tissue).

However, encapsulated lymphoid tissue is responsible for producing lymphocytes, monocytes, and plasma cells, from organs such as the spleen, thymus, and lymph nodes.

Processes

Myelopoiesis

It is known as the process of formation of leukocytes, including eosinophilic granulocytes, basophilic granulocytes, neutrophilic granulocytes, and monocytes. This process is carried out entirely in the bone marrow in the normal adult.

Each type of myeloid or blood cell (eosinophils, basophils, neutrophils and monocytes among others) has a different generative process:

  • Erythropoiesis: formation of erythrocytes.
  • Thrombopoiesis: formation of platelets in the blood.
  • Granulopoiesis: formation of polymorphonuclear granulocytes of the blood: neutrophils, basophils and eosinophils.
  • Monopoiesis: formation of monocytes.

Lymphopoiesis

It is the process in which lymphocytes and Natural Killer cells (NK cells) are formed from a hematopoietic stem cell.

References

  1. AA Maximow (1909). Untersuchungen uber blut und bindegewebe 1. Die fruhesten entwicklungsstadien der blut- und binde- gewebszellan bein saugetierembryo, bis zum anfang der blutbilding unden leber. Archiv Mikroskopische Anatomie und Entwicklungsmechanik. 
  2. C. Ward, DM Loeb, AA Soede-Bobok, IP Touw, AD Friedman (2000). Regulation of granulopoiesis by transcription factors and cytokine signals. Leukemia.
  3. Atlas of plant and animal histology. Recovered from mmegias.webs.uvigo.es
  4. M. Tamez Cantu (1999). Histology manual. Didactic strategy in teaching for the higher level. Didactic proposal to obtain a master’s degree in science teaching with a specialty in biology. University of Nuevo León, Mexico, 135 pp.
  5. Glossary of Medicine. Hematopoiesis. Recovered from glossaries.servidor-alicante.com
  6. Schulman, M. Pierce, A. Lukens, Z. Currimbhoy (1960). Studies on thrombopoiesis. I. A factor in normal human plasma required for platelet production; chronic thrombocytopenia due to its deficiency. Blood Journal.
  7. Palis, GB Segel (1998). Developmental biology of erythropoiesis. Blood Reviews. 
  8. P. Mazzarello (1999). A unifying concept: the history of cell theory. Nature Cell Biology.
  9. S. Welner, PW Kincade, R. Pelayo (2007). Early lymphopoiesis in adult bone marrow. Immunology.
  10. I. Fortoul van der Goes (2017) Histology and Cell Biology, 3e. Mcgraw-HILL Interamericana Editores, SA De CV

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