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Dense Connective Tissues: Dense Irregular

Dense irregular connective tissue is the primary tissue of your dermis. It acts as the gelatinous body stocking that lies deep to your epidermis (the hard candy shell). Unlike dense regular connective tissue, where the pink-stained collagen fibers are oriented in a parallel fashion. In dense irregular connective tissue, the collagen fibers form a mesh-like network with no consistent pattern.  

A microscopic image shows dense irregular connective tissue. Curvy, pink collagen bundles are interwoven throughout a mostly white background. Darker stained fibroblasts are scattered among the collagen.
Figure 1: Microscopic view of dense irregular connective tissue, stained pink and white.

Cells

Fibroblasts are the predominant cells in dense irregular connective tissue. They are responsible for synthesizing the extracellular matrix components. This includes collagen fibers. They maintain the structural integrity of the tissue.  You can see the purple-stained nucleus of the fibroblasts scattered among the collagen.
Macrophages are immune cells. They are involved in phagocytosis. This is the process of engulfing and digesting cellular debris, pathogens, and other foreign particles. Macrophages play a role in the immune response and tissue repair within dense irregular connective tissue.
Mast cells are immune cells that take residence in tissue and release histamine upon triggering.

Fibers

Collagen fibers are the main structural component of dense irregular connective tissue. These pink-stained fibers are arranged in a random, irregular pattern. This arrangement provides the tissue with strength. It also offers resistance to tension from multiple directions. The collagen fibers are primarily composed of type I collagen, which is known for its tensile strength.  While less abundant than collagen fibers, elastic fibers may also be present in dense irregular connective tissue. These fibers contain elastin protein and contribute to the tissue’s ability to stretch and recoil to some extent.

Matrix

The display of dense irregular CT is affected by the process of making a histological slide.  To make a slide, tissues must be dried, fixed, and stained.  The tissue is essentially dehydrated and the watery matrix is removed.  Dense irregular tissue, much like dry skin, starts to crack and flake, creating those white areas unoccupied by tissue.  

Functions

The dense arrangement of collagen fibers in multiple directions gives the tissue strength. It also provides resistance to mechanical forces from various directions. The random orientation of collagen fibers in dense irregular connective tissue allows it to resist tension. It withstands stress from multiple directions. This is particularly important in areas of the body where forces are applied in different planes. Examples include the dermis of the skin. It also includes the capsules surrounding organs that constantly change shape, like the lungs and the digestive organs.

Dense irregular connective tissue forms protective capsules around organs, such as the kidney, spleen, and lymph nodes. These capsules help to contain and support the organs, preventing displacement or damage from external forces. Dense irregular connective tissue is strong and resistant to tension. Its flexible nature allows for some degree of movement and deformation. This flexibility is essential for accommodating changes in body position, movement, and growth.

Locations

Dense irregular tissue is the main component of your dermis. It resembles a gelatinous body stocking located beneath the hard candy shell of your epidermis.  Dense irregular is also found surrounding organs that undergo significant shape deformation. Examples include your digestive organs.  In the deeper locations of the body, dense irregular appears with areolar connective tissue. These tissues form a spectrum where you can find different proportions of each type. In truth, other than the dermis, there are few places you can find representative pictures of dense irregular tissue. Most examples show some invasion of the characteristics of areolar.

Easily Confused With

Areolar CT

Photomicrograph of dense irregular plantar skin at high magnification. The dominant visual element is dense, eosinophilic (pink) collagen fibers arranged in irregular orientation throughout the field of view. Small areas of lighter staining or white space are interspersed between fiber bundles. A small portion of skin tissue is visible that shows skin cells and vessels. Illustrates histologic features of tissue strength and support.
Figure 2: Plantar skin histology. Dense collagen fibers, irregular tissue structure.
Microscopic image of Elastic Connective Tissue (stained with Verhoeff's). Composition features a dense network of dark purple fibers intermingled with red collagen bundles. The image is evenly lit revealing texture and fiber arrangement. Shows connective tissue components with clear structural details.
Figure 3: Dense Irrregular CT of the Dermis of plantar skin. Elastic connective tissue fibers stained with Verhoeff’s stain.
A microscopic image shows dense irregular connective tissue. Curvy, pink collagen bundles are interwoven throughout a mostly white background. Darker stained fibroblasts are scattered among the collagen.
Figure 4: Dermis of think skin with coiled sweat gland.

Figure 1: Small intestine, H&E, 40X Slide 029-1
Figure 2: Thick skin, sole of foot, H&E, 40X Slide 106
Figure 3: Skin, homo, Verhoeff stain, 20X, Slide 033
Figure 4: Thin skin, H&E, 40X Slide 104-2
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.

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General Information
Adipose CT
Areolar CT
Reticular CT
Dense Regular CT
Dense Irregular CT
Elastic CT
Bone CT
Hyaline Cartilage CT
Elastic Cartilage CT
Fibrocartilage CT

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