Where to find reticular connective tissue

Reticular connective tissue 40X. Reticular connective tissue is named for the reticular fibers which are the main structural part of the tissue. The cells that make the reticular fibers are fibroblasts called reticular cells. Reticular connective tissue forms a scaffolding for other cells in several organs, such as lymph nodes and bone marrow. Instead, elastin remains unfolded as a "random coil". Elastin molecules are cross-linked to each other by desmosin and isodesmosin links, which are only found between elastin molecules.

Tensile forces straighten the cross-linked mesh of elastin coils. Ground substance is found in all cavities and clefts between the fibres and cells of connective tissues. Water, salts and other low molecular substances are contained within the ground substance, but its main structural constituent are proteoglycans.

Ground substance is soluble in most of the solvents used to prepare histological sections and therefore not visible in ordinary sections. Proteoglycans are responsible for the highly viscous character of the ground substance. The polysaccharide chains belong to one of the five types of glycosaminoglycans , which form the bulk of the polysaccharides in the ground substance.

Hyaluronan or hyaluronic acid is the dominant glycosaminoglycan in connective tissues. With a length of about 2. Hyaluronan serves as a "backbone" for the assembly of other glycosaminoglycans in connective and skeletal tissue, which results in even larger molecule complexes MW 30,, - ,, Hyaluronan is a major component of the synovial fluid and the vitreous body of the eye.

The remaining four major glycosaminoglycans are chondroitin sulfate, dermatan sulfate, keratan sulfate and heparan sulfate.

These glycosaminoglycans attach via core- and link-proteins to a backbone formed by the hyaluronic acid. This space is called a domain. Neighbouring domains overlap and form a more or less continuous three-dimensional molecular sieve in the interstitial spaces of the connective tissues. The large polyanionic carbohydrates of the glycosaminoglycans bind large amounts of water and cations.

The bound water in the domains forms a medium for the diffusion of substances of low molecular weight such as gases, ions and small molecules, which can take the shortest route, for example, from capillaries to connective tissue cells. Large molecules are excluded from the domains and have to find their way through the spaces between domains.

The restricted motility of larger molecules in the extracellular space inhibits the spread of microorganisms through the extracellular space. A typical bacterium 0. The pathogenicity of a bacterium is indeed to some extent determined by its ability to find its way through the mesh, and some of the more invasive types produce the enzyme hyaluronidase , which depolymerises hyaluronic acid.

Components of the ground substance, collagen and reticular fibres are synthesised by cells of the connective tissues, the fibrocytes. Elastic fibres are synthesised by both fibrocytes and smooth muscle cells. Connective tissue cells are usually divided into two groups based on their ability to move within the connective tissue. Fibrocytes or fibroblasts and fat cells are fixed cells. Macrophages, monocytes, lymphocytes, plasma cells, eosinophils and mast cells are wandering cells.

Fibrocytes are the most common cell type in connective tissues. They are the "true" connective tissue cells. Usually only their oval, sometimes flattened nuclei are visible in LM sections. The cytoplasm of a resting i. This situation changes if the fibrocytes are stimulated, for example, by damage to the surrounding tissue.

In this case the fibrocyte is transformed into a fibroblast, which contains large amounts of the organelles which are necessary for the synthesis and excretion of proteins needed to repair the tissue damage Which ones? Fibrocytes do not usually leave the connective tissue. They are, however, able to perform amoeboid movement.

The terms fibrocyte and fibroblast refer here to the inactive and active cells respectively - at times you will see the two terms used as synonyms without regard for the state of activity of the cell. Reticular cells are usually larger than an average fibrocyte. They are the "fibrocytes" of reticular connective tissue and form a network of reticular fibres, for example, in the lymphoid organs. Fat cells or adipocytes are fixed cells in loose connective tissue.

Their main function is what surprise! If "well fed" the cytoplasm only forms a very narrow rim around a large central lipid droplet. A "starving" adipocyte may contain multiple small lipid droplets and gradually comes to resemble a fibrocyte.

Adipocytes are very long-lived cells. Their number is determined by the number of preadipocytes or lipoblast generated during foetal and early postnatal development. Macrophages arise from precursor cells called monocytes. Monocytes originate in the bone marrow from where they are released into the blood stream.

They are actively mobile and leave the blood stream to enter connective tissues, where they differentiate into macrophages. Macrophages change their appearance depending on the demand for phagocytotic activity.

Resting macrophages may be as numerous as fibrocytes. Liver, rabbit - carbon injected, trichrome Macrophages are usually difficult to distinguish from other cell types in connective tissues.

One way to visualize them is to inject an experimental animal with very fine carbon particles. Macrophages which come into contact with the circulating particles will phagocytose some of them. In sections the particles will be visible as dark, black-brown accumulations in the cytoplasm of the macrophages.

Draw a few macrophages in situ. Macrophages found in the liver are also called Kupffer cells. See also:. Neurons generate electric signals that they pass along to the other neurons or target tissues. In this tutorial, you will find the basic structure of a neuron, the different classes of neurons, and membrane potentials.

It also includes the structure of the nervous system Read More. Reticular fibers contain a high amount of carbohydrates, that is why they can be stained with argentic impregnation and PAS staining. Reticular cells, which are fibroblasts, together with reticular and other collagen fibers, are the mechanical support for lymphoid cells. R eticular connective tissue forms the stroma of bone marrow, spleen, lymphatic ganglia and timus. It is also present in tonsils or amygdala, in the Peyer patches of the ileum, and it is less abundant in other parts of the body.