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
