Transcript What is connective tissue?

Connective Tissue
结 缔 组 织
Department of Histology and Embryology
Medical college in Three Gorges University
• What is connective tissue?
• As the name suggests, it connects the
various tissues of the body and gives them
support.
1) fill the interstices between the specialized
elements
2)hold them together
3)support
Introduction
• General structure and function
Two major constituents
- cell &
- extracellular matrix
• Classification of connective tissue:
Major constituents
cells 细胞
extracellular
Fiber 纤维
matrix
细胞外基质
Ground substance
基质
• Connective tissue proper:
Loose connective tissue
Dense connective tissue
Reticular tissue
Adipose tissue:
Specialized connective tissue
-bone
-cartilage
-blood
• All the cells of connective(supporting)
tissue are derived from mesenchymal
cells. This cell is also named as
undifferentiated mesenchymal cell.
•which are relatively unspecialized and are
capable of differentiation into all the cell types
found in mature supporting tissue.
• Function:
• Connective tissue provides structural
and metabolic support for other tissue
and organs throughout the body.
Loose connective tissue
The cells of supporting /connective tissue
Two categories
fixed cells (intrinsic)
transient cells
Fibroblasts
Fixed cells
Adipose cells
Mast cells
cells
Macrophages
of
Undifferentiated mesenchymal cell
CT
Plasma cell
Transient cells.
Blood cell
Macrophage
Fixed cells are a resident population of
cells that have developed and remain in
place within the connective tissue, where
they perform their functions. The fixed
cells
are
a
stable
population that include:
and
long-lived
Transient cells (free or wandering cells)
originate mainly in the bone marrow and
circulate in the blood stream. Upon
receiving the proper stimulus or signal,
these cells leave the blood stream and
migrate into the connective tissue to
perform their specific function.
1. Fibroblast 成纤维细胞:
•
Fibroblast, which
synthesize
the
extracellular matrix of connective tissue are
derived from undifferentiated mesenchymal
cells.
LM
EM
Function
• Active fibroblast are readily demonstrated
in healing wounds. The nuclei are large and
rounded in shape with prominent nucleoli
(large rounded vesicular nuclei). These are
the cells with multiple processes, and
basophilic cytoplasm.
• In rest phase(inactive ), these are found
along the bundles of collagen fibres and
appear in section as spindle shaped cells
and flattened nucleus with long tapering
ends called fibrocytes (inactive fibroblast).
EM:
RER
Golgi
Function: Fibroblast can synthesize
protein, such as collagen and elastic that
form collagen, reticular and elastic fibers
and ground substances.
• The healing of injury or surgical incisions
depends on the reparative capacity of
connective tissue. The main cell type
involved in repair is fibroblast. (during
wound healing fibrocyte reveres to
fibroblast, myofibroblast )
2.Macrophages: ( histiocytes)巨噬细胞：
They
belong
to
the
mononuclear
phagocytic system analogous to the
monocytes of blood and are distributed
throughout all supporting tissues where
they may show intense phagocytic activity.
• fixed macrophages
• free macrophages
They function in removing cellular
debris and in protecting the body
against foreign invaders.
Secretion: cytokines, growth factor
Antigen presenting cells
• LM: Inactive macrophages are small and
drape themselves it easily confused with
fibroblast goal.
In contrast, actively phagocytic macrophages
are plump.They may be easily recognized by
their large size content of engulfed material.
• EM:
• In quiescent macrophages, lysosomes are
abundant but their number is much reduced
in actively phagocytic cells.
• Function:
1.Actively phagocytic cells are involved
in amoeboid movement and phagocytosis.
2. play an important role in immune
mechanisms: antigen presenting cells.
• In addition to their role as
tissue
scavengers, macrophages play an important
role in immune mechanisms since they are
often the first cells to make contact with
antigens. Lymphocytes are then stimulated
to undergo specific immune responses.
3. Mast cells 肥大细胞:
Mast cells are functionally analogous to
basophils
differences.
but
there
are
structural
• LM: The cells are large round or ovoid in
shape. The nucleus is round and small, relative
to size of the cell, and is often observed by
large number of intensely stained granules in
the cytoplasm.
When stained with certain blue basic dyes
such as toluidine blue the granules bind to
the dye changing its colour to red.
These components of a cell or tissue stain
in a colour different from that of the dye
used, the staining is said to be
metachromatic 异染性.
• Function: Mast cells degranulation
results in the release of histamine and
other vasoactive mediators which
induce the immediate hypersensitivity
response (characteristic of urticaria
（ 荨 麻 疹 ） , allergic rhinitis and
asthma) and anaphylactic shock.
• The granules contain histamine, neutral
proteases heparin and eosinophil cheotactic
factor of anaphylaxis and slow-reacting
substance of anaphylaxis. (SRS-A)
• 4.Plasma cell 浆细胞:
These differentiated cells,which are
derived from B lymphocytes that have
interacted with antigen,produce and
secrete antibodies .
• LM: Plasma cells are large, ovoid cells 20
micronmeter in diameter, with an
eccentrically placed nucleus that have a
relatively short life span of 2 to 3 weeks.
The nucleus is spherical and typically offset
or eccentrically positioned with basophilic
cytoplasm. It is small, not much large than
the nucleus of the lymphocyte.
5. Adipose cells:
• (1)adipocytes, also are derived from
undifferentiated mesenchymal cells.
(2)Adipose cells are fully differentiated and
do not undergo cell division.
• (3)They function in the synthesis and
storage of triglycerides.
• There are two types of fat cells, which
constitute two types of adipose tissue.
• unilocular fat cell: with a single, large
lipid droplet, formed white adipose
tissue, (much more than brown fat)
• multilocular fat cells: with multiple
droplets, form brown adipose tissue.
• In the usual histological preparations , fat
is dissolved during processing of the
tissue and there remains only a thin layer
of cytoplasm slightly thickened in one
area to accommodate the nucleus.The fat
cells can be stained with Sudan and
Scharlach Red which impart these cells
orange and red respectively.
This is a higher
magnification of fat
cell with a large
droplets and
cytoplasm pushed to
the periphery
membrane, nucleus
is flattened against
the membrane also.
• What is about the brown fat cells?
• The nuclei of brown adipocytes are seen to
be eccentrically located within the cell but,
unlike those of white adipocytes, the nuclei
are plump and surrounded by a significant
quantity of strongly eosinophilic cytoplasm
and are not pushed to the periphery.
• 6. Leucocytes in loose supporting tissue:
The appearance of leucocytes within tissue
sections differs greatly from the appearance
seen in blood smears.
Leucocytes:
•
•
•
•
•
lymphocytes
monocytes
Neutrophils
Eosinophils
Basophils
Extracellular matrix
Collagen fiber
fiber
Reticular fiber
extracellular
matrix
Elastic fiber
Ground substance
Ground Substance 基质
•
Ground substance derived its name from being an
amorphous transparent material which has the properties
of a semi-fluid gel. Tissue fluid is loosely associated
with ground substance,thereby forming the medium for
passage of molecules throughout supporting tissues and
for the exchange of metabolites with the circulatory
system.
• Ground substance is basically composed of
glycosaminoglycans (mucopolysaccharide粘多糖) in
the form of hyaluronic acid （透明质酸）and
proteoglycans（蛋白多糖）. These huge molecules
are entangled and electrostatically linked to one
another and water to form a flexible gel through
which metabolites may diffuse.
• It consist of water, carbohydrates and proteins.
Fibers
Collagen fiber 胶原纤维
Collagen is the main fiber type found in
most supporting tissues and is the most
abundant protein in the human body. Its
most notable function is the provision of
tensile strength.
Collagen fibers are seen in bundles.it
is composed of a protein called
Collagen, which is acidophilic due to
its positively charged side groups; thus
in standard H-E preparations.
Collagen is eosinophilic (i.e. pinkstained).
• Reticular fibers 网状纤维:
( 1 )These fibers are finer
( 2 )They are uneven in thickness
( 3)They form a network(or reticulum) by
branching they do not run in bundles
(4)They cannot be stained in H-E but are
able to absorb metallic silver by which they
are stained black.
• Elastic fibers 弹性纤维:
In areola tissue, elastic fibers are much
fewer than those of collagen.they run singly
( not in bundles), branch and anastomose
with other fibers and thinner than those of
collagen (0.1-0.2µm). These are made up of
a protein called elastin. When a fiber is
broken, the ends retract or recoil. Elastic
fibers do not stain with the usual stain for
collagen .
• Physical properties:
• As their name implies elastic fibers can be
stretched (like a rubber band ) and return to
their original length when tension is
released.
The feature of connective tissue proper
• Loose connective tissue 疏松结缔组织:
• It is seen to be made up mainly of bundles of
loosely arranged fibers that appear to
enclose large spaces. Spaces are also called
areolar. Such tissue is referred to as areolar
tissue.
• Loose collagenous tissue supports the
epithelial linings of the gastrointestinal,
respiratory and urinary tracts, form the
deeper layers of the skin and occurs as a
loose interstitial packing in many other
organs.
There are some space in the section, which are also
called areola. Such tissue is referred to as areolar tissue.
• Dense connective tissue:(fibrous tissue)
In many situations the fiber bundles are
much more obvious, and form a dense mass.
This kind of tissue is referred to as dense
connective tissue.
• Dense regular connective tissue 致密结缔组织:
• The bundles of collagen are arranged parallel
to one another in a very orderly manner. This
kind of tissue is called dense regular connective
tissue.
tendon of the muscles
many ligament.
• Dense irregular connective tissue:
• In other situations the collagen bundles do
not show such a regular arrangement, but
interlace in various directions forming
dense irregular tissue.
Dense CT
Dense CT
Capsule invest the
organs
• Reticular tissue 网状组织:
This is made up of reticular fibers. In
many situations (e.g., lymph nodes,
gland )these fibers form supporting
networks for the cells. In some situations
(bone marrow, spleen, lymph nodes) the
reticular network is closely associated
with reticular cells.
• Adipose tissue 脂肪组织
White adipose tissue:白色脂肪组织
It is distributed throughout the body
particularly in the deep layers of the
skin.(it is named as superficial fascia in
anatomy)
• Brown adipose tissue:棕色脂肪组织
• This type of adipose tissue is composed
of multilocular fat cells. This tissue may
appear tan to reddish brown because of
its extensive vascularity and the
cytochromes present in its abundant
mitochondria.