Place in tissue classification
Reticular tissue belongs to the group of connective tissues with special properties. In addition to it, this classification group includes three other types of tissue:
- White adipose tissue;
- Brown adipose tissue;
- Mucous tissue.
It is important to note that mucous tissue is characteristic exclusively of the embryonic period of development and is covered in detail in the embryology course. When studying adult histology, the primary focus is on reticular tissue and the two types of adipose tissue.
Characteristics of reticular cells
Reticular cells are large cellular elements that morphologically closely resemble fibroblasts. They are characterized by a round nucleus located strictly in the center of the cell, as well as numerous long processes.
Within the tissue, these cells contact each other precisely via their processes. Furthermore, they maintain a very close physical connection with reticular fibers. By uniting, the cells and fibers form a unified reticular (three-dimensional) structure that serves as the functional framework of the organ.
Terminological warning! Students often make a gross mistake by calling the cells of the reticular stroma reticulocytes. The term "reticulocytes" refers exclusively to erythrocyte precursors (blood cells). Applying this name to connective tissue stromal cells is strictly prohibited.
Properties of reticular fibers
Reticular fibers are also known by the synonym argyrophilic fibers. Chemically, they are a specific variety of collagen fibers, as they are formed by type III collagen. Their fibrils possess characteristic cross-striations. In size, they are significantly thinner than typical collagen fibers.
The key difference of argyrophilic fibers lies in the high sulfur content of their carbohydrate component. The presence of sulfur determines a number of unique physicochemical properties of this structure:
- Argyrophilia — pronounced affinity for silver compounds and the ability to actively bind them.
- Branching — high capacity to form connections (anastomoses) between neighboring fibers.
- Resistance — unlike ordinary collagen, these fibers are completely devoid of the ability to swell.
Localization and microscopic picture
In the human body, reticular tissue forms the stroma of the main organs of hemopoiesis and immune defense: red bone marrow, spleen, and lymph nodes.
Two completely different types of staining are used for histological diagnosis and preparation analysis, each demonstrating specific aspects of the tissue:
- Hematoxylin and eosin staining. This method provides excellent visualization of the reticular cells themselves and their processes connecting the elements to each other. Free blood cells (e.g., lymphocytes) can be easily seen within the meshes of this cellular network.
- Silver nitrate impregnation. This method aims to reveal reticular fibers. Due to their argyrophilia, the fibers stain a deep black color and appear as a dense network. The spatial organization with this staining looks as follows: reticular cells are located in the nodes of the black network (although they are usually indistinguishable with this method), while numerous free blood cells lie within the meshes of the network. The cellular composition within the meshes varies depending on which hemopoietic organ is being examined.
Briefly: answers to topical questions
What is the embryonic origin of reticular tissue?
The embryonic source of reticular tissue development is mesenchyme. This tissue belongs to the stromal component present in both myeloid and lymphoid hemopoietic tissues. The cells of the stromal component, representing a variety of connective tissue, are of mesenchymal origin. Reticular tissue forms the basis of the red bone marrow, lymph nodes, and spleen, acting as a supportive framework and microenvironment for hemopoietic cells, which also develop from mesenchyme.
What functions, besides forming the supportive framework, does reticular tissue perform?
In addition to forming a three-dimensional supportive network for hemopoietic cells, reticular cells participate in creating the microenvironment of hemopoietic tissue. They produce reticular fibers (type III collagen) and amorphous ground substance, forming a reticular structure. Reticular cells also secrete hemopoiesis-regulating factors. Developing blood and immune system cells are located within the meshes of this network, maintaining a close connection with the stroma.
What is the exact cellular composition of the free cells located within the meshes of the reticular tissue of a lymph node?
Sources do not provide an exhaustive precise list of all free cells in the meshes of the reticular tissue of a lymph node. It is confirmed that the stroma of the lymphoid tissue of a lymph node is formed by reticular tissue, with lymphoid cells and macrophages located in its meshes. In the outer cortex, lymphoid nodules are B-dependent zones: primary nodules are compact homogeneous accumulations of small B-lymphocytes, while secondary ones consist of a cap and a germinal center where antigen-dependent proliferation and differentiation of B cells into immature plasma cells and memory B cells occur. Interfollicular accumulations and the paracortical region belong to T-dependent zones; antigen-dependent proliferation and differentiation of T-lymphocytes occur in the paracortical region.
Argyrophilia is easy to remember: Silver reacts with Sulfur (the carbohydrate component of the fibers contains a lot of sulfur, which is why they stain black with silver nitrate).
Class and exam questions
Can stromal cells of hemopoietic organs be called reticulocytes?
No, this is a gross mistake. Reticulocytes are immature forms of erythrocytes. Stromal cells are called exclusively reticular cells.
What is the main chemical difference between reticular fibers and regular collagen fibers?
The key difference lies in the high sulfur content of the carbohydrate component, which imparts argyrophilia and resistance to swelling.
What staining method is used to visualize reticular fibers?
The silver nitrate impregnation method is used to reveal reticular fibers. The fibers acquire an intense black color.
Where are blood cells located relative to reticular tissue?
Blood cells (e.g., lymphocytes) are located in the free spaces — the meshes of the unified three-dimensional network formed by reticular cells and fibers.
What else to study on this topic
- Features of the microscopic structure of white adipose tissue
- Functions and localization of brown adipose tissue in the body
- Cellular composition of reticular tissue meshes in the red bone marrow
- Features of lymphocyte distribution in the reticular stroma of the spleen
- Structure and role of mucous tissue in the embryonic period of development
Master the entire topic in the "Histology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Reticular tissue" and 3,485 more pages of the subject
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- 137 video lessons on the subject
Other topics in the section "Proper connective tissues. Connective tissues with special properties"
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