Healthcare and Medicine Reference
In-Depth Information
A
Fig. 1.7 The fascial matrix of the lower leg (of a rat), showing the
histological continuity among synergistic and even antagonistic
muscles. This 3-D reconstruction, using three frozen sections of
the anterior and lateral crural compartments, enhances the
connective tissue structures within each section. The smallest
divisions are the endomysial fibers which surround each muscle
fiber. The 'divisions' between these muscles - so sharp in our
anatomy texts - are only barely discernable. (Used with kind
permission from Prof. Peter Huijing, Ph.D., Faculteit
Bewegingswetenschappen, Vrije Universiteit Amsterdam.)
cells, fat cells, and osteocytes among others - it is the
fibroblasts and their close relatives that produce most of
the fibrous and interfibrillar elements of such startling
and utilitarian variety. It is to the nature of these intercel-
lular elements that we now turn our attention.
The dramatis personae of the connective tissue ele-
ments is a short list, given that we are not going to
explore the chemistry of its many minor variations.
There are three basic types of fibers: collagen, elastin,
and reticulin (Fig. 1.8). Reticulin is a very fine fiber, a
kind of immature collagen that predominates in the
embryo but is largely replaced by collagen in the adult.
Elastin, as its name implies, is employed in areas such
as the ear, skin, or particular ligaments where elasticity
is required. Collagen, by far the most common protein
in the body, predominates in the fascial net, and is
readily seen - indeed, unavoidable - in any dissection
or even any cut of meat. There are around 20 types of
collagen fiber, but the distinctions need not concern us
here, and Type 1 is by far the most ubiquitous in the
structures under discussion. These fibers are composed
of amino acids that are assembled like Lego® in the
endoplasmic reticulum and Golgi complex of the fibro-
blast and then extruded into the intercellular space,
where they form spontaneously (under conditions
described below) into a variety of arrays. That the trans-
parent cornea of the eye, the strong tendons of the foot,
the spongy tissue of the lung, and the delicate mem-
branes surrounding the brain are all made out of colla-
gen tells us something about its utilitarian variety.
B
Fig. 1.6 A section of the thigh, derived from the National Library
of Medicine's Visible Human Project by Jeffrey Linn. The more
familiar view in (A) includes muscle and epimysial fascia (but not
the fat and areolar layers shown in Fig. 1.24). The view in (B)
gives us the first glimpse into what the fascial system would look
like if that system alone were abstracted from the body as a
whole. (Reproduced from US National Library of Medicine's Visible
Human Data® Project, with kind permission.)
separating ones. It binds every cell in the body to its
neighbors and even connects, as we shall see, the inner
network of each cell to the mechanical state of the entire
body. Physiologically, according to Snyder, 1 3 it also 'con-
nects the numerous branches of medicine'.
Part of its connecting nature may lie in its ability to
store and communicate information across the entire
body. Each change in pressure (and accompanying
tension) on the ECM causes the liquid crystal semicon-
ducting lattice of the wet collagen and other proteins to
generate bioelectric signals that precisely mirror the
original mechanical information. 1 4 The perineural
system, according to Becker, is an ancient and important
parallel to the more modern conduction along nerve
membranes. 1 5
Although there are a number of different cells within
the connective tissue system - red blood cells, white
blood cells, fibroblasts, mast cells, glial cells, pigment
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