Connective tissue

What is connective tissue? As the name suggests, it connects the vari

ous tissues of the body and gives them support.

1.       General features:

1)   small number of cells and large amount of extracellular ground substance

2)  extracellular is composed of fibers and amorphous ground substance-matrix

3)   all of them originate from mesenchyme-embryonal CT

4) have functions of connection, supporting, protecting, nutrition, defence and repairing

mesenchyme---mesenchymal cell: /structure: stellate/star in shaped with

processes a large nucleus,with clear n

ucleoles slight basophilic cytoplasm /function: a.    undifferentiated cell b. multiple developmental pot

ential→CT cell, SM and endothelial cell

---matrix

2.       Classification ---CT in narrow sense means connetive prop

er which include loose CT, dense CT, adipose T and reticular tissue

---CT in wide sense includes cartilage, bone and blood

3.  Loose connective tissue(areolar tissue)

features: have more types of cells and less fibers

functions: connection, supporting, defence and repairing

consists of cells, fiber and ground substance

cells

extracellular

matrix

Major con

stituen

ts

Fiber

Ground substance

1) cells: seven types of cells are present in LCT

cells

of

CT

Fixed cells

Transient cells

Fibroblasts

Adipose cells

Mast cells Macrophage

s

Undifferentiated mesenchymal cell

Plasma cell

Blood cell

Macrophage

① fibroblast

---structure: LM: large,flattened cell with processes- stellate in sha

ped Large ovoid pale nucleus-contain more fine chro

matin, with clear one-two nucleoli Weakly basophilic cytoplasm-homogeneous

EM: rich in RER, Golgi appatatus and free riboso

me---function: synthesize fibers and ground substa

nce

Synthesis of collagenous fiber

Three steps: a.synthesis of procol

lagen(RER) → process(Golgi) → out of cell

b.procollagen→ tropocollagen → fibril

c.fibril → collagenous fiber

*fibrocyte: still state or inactive fibroblast---structure: spindle-shaped, small N:small,dark stained Acidophilic cytoplasma EM: less organelles

---function: become into fibroblast for repairing

EM:

RER

Golgi

②macrophage---structure:

LM: round or ovoid-irregular in shape when it

have short blunt processes_pseudopodium Small and dark nucleus Acidophilic cytoplasm

EM: rich in a.  lysosome b. Phagosome← phagocytosis and pinosome ←pinocytosis c.  Remnant d.  Microfilament and microtubule

---function: a.    Chemotaxis: chemotactic factor(TNFα 、 I

FN (interferon) or interleukin) b. phagocytosis: Special phagocytosis: recognize Bacterium, vi

rus and foreign cell non special: carbon particles, dust and dead c

ells *Phagosome(pinosome) + primary lysosome

→secondary lysosome →remnants

c.  secretion: lysozyme, complement and interleukin-I (IL-1)and interferon(INF)

b.  antigen presenting function:

*capture antigen→processes→+ MHC II molecule (major histocompatibility complex molecules) →antigen-MHC II complexes→ TLC/BLC

③plasma cell---structure:

LM: round or ovoid Round eccentrically-located nucleus with

more spot-liked heterochromatin Basophilic cytoplasm

EM: rich in parallelly arranged RER, free ribosome and Golgi complex

---function: synthesize and secrete immunoglobulin, Ig-antibody

④mast cell

---structure:

LM: round and large cell Small dark-stained nucleus Basophilic secreting granules

Basophilic secreting granules: heparin:an anticoagulant Histamine: cause cap. permeability↑, cap.

leakage to form oedema and contraction of SM

Eosinophil chemotactic factor

Cytoplasm contain: leukotriene- slow reaction substance

Function: Mast cells degranulation r

esults in the release of histamine a

nd other vasoactive mediators whic

h induce the immediate hypersensit

ivity response (characteristic of urti

caria （ wheal-itch ） , allergic rhinit

is (sneeze) and asthma (cough)) an

d anaphylactic shock.

⑤adipose cell(fat cell)

---structure: large, round or polygonal flattened ovoid nucleus located on one side of cell thin layer of cytoplasm a large lipid droplet

---function: synthesize and store fat

This is a higher

magnification of fat

cell with a large

lipid droplets and

cytoplasm pushed to

the periphery

membrane, nucleus

is flattened against

the membrane also.

⑥undifferentiated mesenchymal cell

---structure:similar to fibrocyto

---function:multidifferentiating potential

⑦leukocytes: neutrophil,acidophil and lymphocyte

2) fibers

①collagenous fiber(white fiber)

LM: Main fiber 1-20 um in diameter Belt-liked wave and branch to form a network Eosinophilic

EM: parallel-arranged fibrilsFibril: 20-200nm in diameter Have periodic cross striation at 64nm interval*formation: Extracellular polymerize

collagen(type I and III) →collagenous fibril → collagenous fiber

② elastic fiber (yellow fiber) LM: thinner and less, 0.2-1.0 um Slight red(HE), purple(aldehyde fuchsin) or brow

n(orcein) Branch and form a network EM: core: elastin-low electron density Peripheral: microfibril 10-12 nm, electron dense ↑ fibrillin

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.

③reticular fiberLM: thin and less,0.2-1.0 um in diameter Branch to form network Argyrophilic fiber(silver impregnation method)EM: type III collagen 64nm cross striation---distribution: reticular tissue connecting portion, e.g.reticular lamina

3) ground substance

---amorphous colloidal substance

---consists of proteoglycan, glycoprotein and tissue fluid

①proteoglycan Large molecular complex (polysac

charide)

---glycosaminoglycans: chondroitin sulfate keratin sulfate dermatan sulfate heparin sulfate hyaluronic acid: 2.5um long

--protein

*molecular sieve

② glycoprotein: proteins---fibronectin cells←fibronectin→collagen

↓ proteoglycan---laminin---chondronectin---function: Connection affect the differentiation and movement of cells

③ tissue fluid

tissue

artery → Tissue fluid → vein →blood steam

cells dehydration edema

4.    Dense connective tissue

---more fiber

---connection and supporting

1) regular DCT: parallelly-arranged collagenous fibers tendon cells: /special fibroblast

/wing-liked processes

---distribution: tendons, ligament and cornea

2) irregular DCT: Fiber arranged in bundles,runing in different d

irection Fibroblast less ground substance---distribution: dermis, sclera and capsule of so

me organs

3) elastic T: elastic fiber in bundles or in membrane ligament and large artery

5.       adipose tissue---LCT+fat cells---white fat T: single fat cell distribution in subcutaneous tissue, mesenteriu

m---brown fat T: fat cell contain many small lipid droplets, rich in large mitochondria centrally-located nucleus rich in cap. distribution: neonate

6.    reticular tissue---reticular cells: stellate with processes-form network round, ovoid and pale nucleus with 1-2 nucle

oli EM: rich in RER---reticular fiber: connect to form network---distribution: hemopoietic tissue and lymphatic

tissue