INTRODUCTION
Connective tissue consists of
cells and extracellular fibers (protein
polymers) embedded in a matrix
consisting of ground substance and
fluid. Connective tissue can be divided
into three major types: embryonal,
proper, and special connective tissues.
Mesenchyme and mucous connective tissue are classified as embryonal connective
tissue. Mesenchymal connective tissue is a transitory tissue that disappears as the embryo
develops and differentiation occurs. The primary constituents are the mesenchymal cells which
are stellate or fusiform in shape with many cytoplasmic procecesses.
ACTIVITY
Examine a section of a pig or chick embryo. Identify and draw the mesenchymal
connective tissue situated between the neural tube and superficial ectoderm.
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REVIEW QUESTION
1. What is/are the function/s of this connective tissue type?
INTRODUCTION
Mucous connective tissue is a
characteristic of the umbilical cord
surrounding the umbilical vessels. It is also
found in the subepidermal regions of a
developing embryo and wattles and combs
of gallinaceous birds.
ACTIVITY
Examine under HPO any of the abovementioned tissues. In the space below, draw and
label the collagenous fibers, fibroblasts and matrix (Wharton’s jelly).
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REVIEW QUESTION
1. What is the Wharton’s jelly?
INTRODUCTION
Connective tissue proper (also known as proper connective tissue) includes the general
types of connective tissue: loose and dense; regular and irregular; and reticular, elastic, and
adipose.
The loose or ordinary connective tissue contains aggregates of loosely arranged fibers
and a relatively large number of cells. All three types of fibers (collagenous, elastic, and reticular
fibers) are present in this type.
The majority of cells are
fibroblasts, although macrophages
(also known as histiocytes or tissue
monocytes, which are white blood
cells that have moved out of the
bloodstream and into tissue),
plasma cells (a type of tissue
lymphocyte), and mast cells (cells
that develop in the bone marrow in
separate cell lines from white blood
cells) can also be found. Other
white blood cells, which include
tissue eosinophils, neutrophils,
basophils, and lymphocytes, can
occasionally be seen, but they are in
an unchanged state from what can
be observed in blood.
Loose connective tissue is found under the mucosal epithelium in most places of the
body, forms the lamina propria and is the connective tissue that attaches the epithelial cells of
the serosa to organs.
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ACTIVITY
Examine the colon and note that one surface is indented by pits that are lined by
columnar epithelial cells. Immediately beneath these cells is the loose connective tissue called
lamina propria.
In the space below, draw and label the cells, fibers, and tissue parts.
REVIEW QUESTION
1. What is/are the function/s of this connective tissue type?
INTRODUCTION
Reticular connective tissue is composed of
a fibrous network of reticular fibers. These fibers
(consisting mainly of type III collagen) are too thin
to stain in ordinary histological preparations. They
become visible only when the tissue or organ is
stained with silver stain.
Fibroblasts are the predominant cell types.
Reticular connective tissues comprise the stroma
of all lymphatic organs (spleen, lymph nodes,
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hemal nodes and tonsils), diffuse and solitary lymphatic nodules and bone marrow.
ACTIVITY
Examine a prepared section of reticular connective tissue under HPO. In the space below,
draw and label the cells, fibers, and tissue parts.
REVIEW QUESTION
1. What is/are the function/s of this connective tissue type?
INTRODUCTION
Adipose tissue or fat is a
specialized type of connective tissue
composed of a homogenous cell
population of adipocytes or fat cells.
There are two types of adipose
tissue, white (or unilocular) and
brown (or multilocular).
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ACTIVITY
Examine a prepared tissue section under LPO and HPO.
Individual adipose cells appear as empty cells because alcohol dissolves fats in routine
histologic preparation of the tissue. The thin peripheral ring of cytoplasm and the flattened
peripheral nucleus, coupled with the large central vacuole accounts the "signet ring" appearance
of fat cells.
In the space below, draw and label the cells and tissue parts.
REVIEW QUESTIONS
1. What is/are the function/s of this connective tissue type?
2. Where can you find brown or multilocular adipose tissue?
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INTRODUCTION
Dense connective tissue
contains thicker and more
densely packed collagen fibers,
with fewer cell types and less
ground substance. The collagen
fibers
in
dense
irregular
connective tissue exhibit a
random
and
irregular
orientation. This tissue makes up
the dermis of the skin, the
submucosa of the digestive tract,
the capsule of organs and joints,
the
perichondrium
around
cartilage, and the periosteum.
In contrast, dense regular connective tissue contains densely packed collagen fibers that
exhibit a regular and parallel arrangement. This type of tissue is found in the ligaments, tendons,
and aponeuroses.
In both connective tissue types, fibroblasts are the most abundant cells, which are
located between the dense collagen bundles.
ACTIVITY
Examine the dermis of the skin specifically in the reticular zone for the dense irregular
connective tissue. Note that the term reticular refers to the reticular network arrangement of
the collagenous fibers in various directions) and not the reticular fibers. Note the pattern of
abundant bands of thick collagen fibers. Also look for spindle-shaped fibroblasts.
For the dense regular connective tissue, examine a prepared section of a tendon,
ligament or aponeuroses. Note the layer of parallel collagen fibers, w hichstain intensely pink.
The wave-like appearance is an artifact from processing; under natural conditions, this tissue
would be very linear in appearance.
In the space below, draw and label the cells, fibers, and tissue parts.
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REVIEW QUESTIONS
1. What is/are the function/s of dense irregular connective tissue?
2. What is/are the function/s of dense regular connective tissue?
INTRODUCTION
Elastic connective tissue is characterized by
numerous regularly and irregularly arranged elastic fibers.
When stretched, elastic fibers return to their original size
(recoil) without deformation. The major cell type is the
fibroblast.
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This tissue is found in the ligamentum nuchae, in the vocal ligaments and in the walls of
arteries and veins.
ACTIVITY
Examine a prepared section of elastic connective tissue or ligamentum nuchae under LPO
and HPO. Note the bright pink-staining elastic fibers which branch and anastomose with each
other. In cross section, the elastic fibers are larger than collagenous fibers.
In the space below, draw and label the cells, fibers, and tissue parts.
REVIEW QUESTIONS
1. What is/are the function/s of this connective tissue type?
2. Cite the difference/s between this connective tissue type and DWFCT.
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