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Connective tissue Body contouring


Connective tissue Body contouring

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									Chapter 5. Connective tissue
      Connective tissues form the            allow for a tight coiling of the molecule.
structural and architectural framework of    Collagen molecules have a high
the body. In a connective tissue the cells   concentration of hydroxylated proline
are widely scattered and separated by        and lysine, which is unique to collagen.
an extracellular matrix. Connective          Individual collagen molecules join
tissues are composed of three major          together to form collagen fibrils, which
components: cells, fibers, and ground        has an increase in strength similar to a
substance. Specific connective tissues       braided rope. Multiple fibrils will
will be classified based on the types and    sometimes aggregate in thicker bundles
concentrations of these basic                to form collagen fibers . The high
components. The extracellular matrix is      concentration of proteins in collagen
composed of ground substance and             fibers stain pink in H&E stained
fibers. The ground substance includes        sections. Collagen fibers of the papillary
proteoglycans and glycosaminoglycans         layer of the dermis are thin and
dissolved in tissue fluid. These hydrated    organized in a loose manner. Collagen
molecules help to give the matrix a gel-     fibers of the reticular layer of the dermis
like consistency. The matrix viscosity       are thicker and have a denser, more
and rigidity is determined by the amount     irregular appearance. When using a
and type of glycosaminoglycans.              trichrome stain, collagen fibers will
Glycosaminoglycans associate with core       appear bluish-green.
proteins to make proteoglycans.

Figure 5-1. Ground substance.

Fibers:                                      Figure 5-2. Collagen
      Collagen fibers have great tensile
strength and are highly resistant to
stretching, weight for weight stronger
than steel. Collagen is the most
abundant protein in the body. Collagen
fibers are formed by the interaction of
individual collagen molecules (3
polypeptide chains wrapped in a triple-
helix) in a staggered manner to form a
structure similar to a braided rope.
Collagen is composed of a high-
concentration of amino acid glycine to
TABLE 5.1:        Types of Collagen
Type I           most abundant and widespread       large fibers and fiber bundles
Type II          thin fibrils                       cartilage matrix
Type III         like I, but more glycosylated      thin fibrils surround and support soft tissues.
Type IV          doesn't form fibers or fibrils.    in basal lamina
Type V           placental basement membranes       blood vessels.

       Elastic fibers are very flexible and        In H&E preparations, elastic fibers
stretchable, able to stretch to 150% of            cannot be distinguished. In aldehyde-
their length and return without breaking.          fuchsin stained tissues, elastic fibers will
Elastic fibers are found in connective             appear purple.
tissues where these properties are
required to allow organs to expand and
return to their normal shape. Elastic
fibers are convey the ability of a
connective tissue such as a mesentery to
stretch in many directions. This is
illustrated by some fibers being stretched
(appearing straight) will fibers in a
different orientation are relaxed
(appearing almost coiled).

                                                   Figure 5-4. Appearance of reticular fibers.

                                                         Reticular fibers are similar to
                                                   collagen fibers but thinner and more
                                                   glycosylated (mainly type III collagen
                                                   and glycoproteins). Reticular fibers form
                                                   a fine network to support tissues of soft
                                                   organs, such as lymphoid organs,
                                                   hematopoeitic organs, and the liver. To
                                                   visualize reticular fibers it is necessary
Figure 5-3. Elastic fibers in a loose connective   to stain with silver salts so that the
tissue.                                            reticular fibers appear black. Reticular
                                                   fibers form a delicate scaffold which
      Elastic fibers may also be found in          often allows motile cells to move about
sheets in regions of the body that need to         the tissue, such as within lymph nodes.
stretch extensively such as in the walls
of muscular and elastic arteries. Further          Fixed cells:
examples of connective tissues with                         Fibroblasts are the major class
elastic fibers include interalveolar septa,        of fixed or resident connective tissue
bronchi and bronchioles of the lungs,              cells. Fibroblasts remain in the
and vocal ligaments. Elastic fibers are            connective tissue where they synthesize,
much thinner than collagen fibers.                 secrete, and maintain the connective
Elastic fibers will appear a blue-black or         tissue. These cells have elongated nuclei
reddish-purple with an elastic fiber stain.        and their cytoplasm often cannot be
observed because the cell is normally       identify a macrophage, it is often
pressed against the collagen and are the    necessary to see some phagocytosed
same color as the collagen fibers.          material within the cell.

                                                      Lymphocytes are circulating
                                            white blood cells found throughout
                                            many connective tissues, especially in
                                            regions likely to see foreign antigens
Figure 5-5. Fibroblast.                     such as the connective tissue (lamina
                                            propria) of the small intestine.
Wandering cells:                            Lymphocytes are cells with small dark
         Wandering or immigrant cells are   (very heterochromatic) nuclei with very
cells which come form the blood system.     little cytoplasm. A region of lymphocyte
Some cells, such as lymphocytes, move       infiltration will appear very dense and
through the connective tissue and return    basophilic.
to the circulatory system. other cells,
such as macrophages, differentiate and
take up permanent residence in the
connective tissue.

Figure 5-6. Macrophage.

        Macrophages are a phagocytic
connective tissue cell. These cells are     Figure 5-7. Lymphocytes.
derived from monocytes, which leave
the blood stream and differentiate into
                                            Some lymphocytes (B lymphocytes) will
macrophages within the connective
                                            differentiate into plasma cells, which are
tissue. They are lighter staining cells
                                            actively synthesizing and secreting
with an irregular shaped or bumpy           antibodies in response to a foreign
euchromatic nucleus, and abundant
                                            antigen. Plasma cells are more numerous
lysosomes. Macrophages are long-
                                            during immune responses. These cells
lived (weeks to years) and are actively
                                            have an eccentric nucleus (pushed over
involved in the phagocytosis of bacteria,
                                            to one side). The nucleus has a clumped
tumor cells, foreign antigens, and the      heterochromatin pattern called either
remodeling of tissues. To conclusively
                                            cartwheel or clock-face. The cytoplasm
is normally slightly basophilic with a      Neutrophils in the connective tissue are
clear zone of Golgi complex near the        the bodies first line of defense against
nucleus.                                    bacteria.

         Mast cells regulate the
permeability of capillaries. These round
or oval cells have an oval nucleus,
considerable cytoplasm packed with
numerous basophilic granules, and are
often observed near capillaries. ,These
cells release heparin and histamine from
the basophilic granules in response to an
allergen or antigen binding to specific     Figure 5-9. Neutrophil.
IgE antibodies along the surface of the
mast cell.                                  Types of connective tissues:
                                            Connective tissue proper
                                                     A loose or areolar connective
                                            tissue , such as a mesentery, is composed
                                            of relatively few collagen and elastic
                                            fibers, abundant ground substance and a
                                            limited number of cells. The cells are
                                            mainly fibroblasts.

                                                     A loose cellular connective
Figure 5-8. Mast cell.                      tissue has the same basic pattern of
                                            collagen fibers, elastic fibers, and
         Eosinophils, basophils, and        fibroblasts; but also has a greater
neutrophils are circulating granulocytes    population of migrating cells such as
(a class of white blood cells), which are   lymphocytes which give the connective
found in the connective tissue as well as   tissue a more cellular appearance. A
within the circulatory system.              loose cellular connective tissue is
                                            normally found as the lamina propria
         Eosinophils have a bi-lobed        under the epithelial lining of the
nucleus and many eosinophilic               digestive tract.
cytoplasmic granules. The increased
presence of eosinophils usually indicates            In a dense irregular connective
an allergic reaction in response to         tissue , the fiber components are much
parasitic infections.                       larger but appear in a somewhat random
                                            or woven manner. There is little ground
        Basophils also have a lobed         substance and few cells. A good
nucleus, but are filled with basophilic     example of a dense irregular connective
cytoplasmic granules. Basophils are         tissue is the reticular layer of the dermis.
most commonly found at sites of             The irregular pattern formed by the thick
inflammation.                               collagen bundles allow for strength in
                                            many directions. Therefore a dense
       Neutrophils normally have a          irregular connective tissue is also found
lobed nucleus and cytoplasmic granules.
lining the capsules of many organs such
as the kidney, spleen, and liver.

         In a dense regular connective
tissue , the fibers are packed together and
oriented in one direction. The fibers do
not have to be perfectly straight and
parallel to one another. In a relaxed
tendon, the dense regular connective
tissue may have a slightly wavy
appearance, with all the collagen fibers
running in the same general direction. A
dense regular connective tissue will be       Figure 5-10. White Adipocytes.
found in tendons, ligaments, and the
cornea.                                                Brown adipose tissue (brown
                                              fat) is a multilocular fat, having
        A reticular connective tissue is      multiple smaller lipid droplets in the cell
composed of primarily reticular fibers,       rather than a single lipid droplet as in
which form a supportive network for soft      white fat and a spherical nucleus. Brown
organs. A reticular connective tissue has     adipocytes have many mitochondria, and
an anastomosing appearance with more          it is the mitochondrial cytochromes
open spaces than other types of               which give the cells a reddish-brown
connective tissues. A reticular               color. Regions of brown adipocytes
connective tissue is found in                 often have a glandular appearance.
hematopoeitic organs, lymphoid organs,        Brown fat is involved in heat production
and the liver.                                and is important in thermoregulation in
Adipose tissue:
         White adipose tissue (white fat)
is a specialized connective tissue for the
storage of lipids. White adipose tissue
appears as a vacuolated, pale region
resembling chicken wire. Individual fat
cells (adipocytes) have a non-staining
central region as the single large lipid
droplet has been removed in tissue
processing. The nucleus is pushed to the
edge of the cell and a pale ring of
cytoplasm surround the site of the lipid
droplet giving the cell a signet ring
appearance. White fat is important for
energy storage, shock absorption,
thermal insulation, and body contouring.      Figure 5-11. Brown Adipocytes.
It is located in the hypodermis and
throughout other loose supportive

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