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Fibrous connective tissue
Last reviewed: 04.07.2025
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Fibrous connective tissues include loose and dense fibrous connective tissues. Dense fibrous connective tissue, in turn, has two varieties - unformed and formed dense connective tissue.
Loose fibrous connective tissue is located mainly along the blood and lymphatic vessels, nerves, forms the stroma of many internal organs, as well as the proper plate of the mucous membrane, submucosa and subserosa, adventitia. It contains numerous cells: fibroblasts, fibrocytes, macrophages, mast cells (tissue basophils), adipocytes, pigment cells, lymphocytes, plasma cells, leukocytes. In the intercellular substance of loose fibrous connective tissue, amorphous matter predominates, and the fibers are usually thin. There are few fibers, they are located in different directions, so such tissue is called loose.
Dense fibrous connective tissue, thanks to its well-developed fibrous structures, performs mainly supporting and protective functions. The intercellular substance is dominated by fibers, there is little amorphous substance, and the number of cells is less significant. Connective tissue fibers are either intertwined in different directions (unformed dense fibrous tissue) or are located parallel to each other (formed dense fibrous tissue).
Unformed dense fibrous connective tissue forms sheaths for muscles, nerves, organ capsules and trabeculae extending from them into the organs. This tissue forms the sclera of the eye, the periosteum and perichondrium, the fibrous layer of joint capsules, the reticular layer of the dermis, the heart valves, the pericardium, and the dura mater.
Formed dense fibrous connective tissue forms tendons, ligaments, fascia, interosseous membranes. Parallel collagen fibers are thin bundles of the 1st order. Between them are the so-called tendon cells with characteristic dark nuclei of an oblong shape. Bundles of collagen fibers of the 1st order are combined into thicker bundles of the 2nd order, which are separated by layers of fibrous connective tissue. These bundles are formed by collagen fibers tightly packed into layers, which in adjacent layers cross almost at a right angle. Between the layers lie flattened multi-branched fibrocytes.
Elastic connective tissue forms the elastic cone of the larynx and its vocal cords, yellow ligaments, and participates in the formation of the walls of elastic arteries (aorta, pulmonary trunk). The main elements of this tissue are elastic fibers closely adjacent to each other, between which lie a small number of fibrocytes. A fine-fibrillar network formed by collagen and reticular microfibrils envelops the elastic fibers.
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