Histology of Dense irregular connective tissue

Dense connective tissue  is characterized by large, robust collagen fibres with less number of connective tissue cells.

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 Fibres are so numerous that the key identifying trait of this tissue is the absence of open spaces between cells or fibres. Since the protein fibres are the dominant component of these tissues, the types of fibres and their orientation within these tissues is the basis for the naming scheme. Dense CTs contain either collagen or elastic protein fibres; therefore, there are dense collagenous CTs and dense elastic types. The collagenous types are far more abundant and are called fibrous or ‘white’ CT. Elastic fibres, on the other hand, appear yellow in unstained tissues and are commonly referred to as ‘yellow’ CT (e.g. the yellow ligaments of the spine). Fibroblasts are the only cells visible and are arranged in rows between the fibres. Their function is to create the collagen fibres of the tissue.

The main roles of dense CT are to transmit forces over a distance and to connect different organs/muscles. Collagen fibres are disposed along the direction of mechanical loads present in that specific tissue. The capacity of dense CT to resist mechanical stress is directly related to the structural organization of the ECM and above all, the collagen fibres.

The dense CT is subclassified as follows:

•Dense, irregular CT has irregularly arranged collagen fibres and usually comprises the dermis and fasciae. In the last few years, it has been demonstrated that the irregular appearance of deep fasciae may be due to its multilayered structure, but in actuality each layer presents its own regularity (see Chapter 3). Consequently, the deep fasciae could be classified as dense regular CT.

•Dense, regular CT is a white, flexible tissue that contains tightly packed bundles of collagen fibres. All of these fibres run in one direction and are arranged parallel to the direction of forces exerted on the particular body part where the tissue is located. This arrangement is typical of tendons and ligaments, but according to recent studies (Benetazzo et al 2011) the deep fasciae could also be classified in this group. Purslow (2010) demonstrated that the epimysium and perimysium have a very specific organization that also may classify them as dense, regular CT, and Huijing and Baan (2003) demonstrated this tissue’s role in force transmission (see Chapter 3). Finally, a specific discussion of the endomysium is necessary as it is not clear whether this has a structure similar to a microtendon (Purslow 2010) or if it is better classified as loose CT (Testut 1905). In the following chapters, the characteristics and functions of the deep fasciae, epimysium and perimysium will be described in greater detail.

Histology of Dense irregular connective tissue

1. connective tissue cells are less 

2. fibers are more, irregular  and loosely arranged 

Example : submucosa of GIT