connective tissue 结 缔 组 织 department of histology and embryology medical college in three...

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:

cells 细胞

extracellular

matrix

细胞外基质

Major con

stituen

ts

Fiber 纤维

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

Two categories

fixed cells (intrinsic)

transient cells

The cells of supporting /connective tissue

cells

of

CT

Fixed cells

Transient cells.

Fibroblasts

Adipose cells

Mast cells

Macrophages

Undifferentiated mesenchymal cell

Plasma cell

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 and long-lived

population that include:

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 but there are structural

differences.

• 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

extracellular

matrix

fiber

Ground substance

Elastic fiber

Reticular fiber

Collagen fiber

• 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 基质

• 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.

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.

Fibers

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. pink-

stained).

• 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.

• 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.

The feature of connective tissue proper

• 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.