October 12th, 2004
Histology SSN
Irene Lo (ijl2101)
Missy Walker (maw2106)
CONNECTIVE TISSUE
I.
INTRODUCTION
- derived from mesenchyme (mostly mesoderm)
- divided into: connective tissue proper, bone, cartilage, lymph
II. COMPONENTS OF CONNECTIVE TISSUE PROPER
Connective tissue is composed of cells and their secreted ECM (fibrous proteins, ground substance, and fluid). The
combination and ratio of each determines the function & role of various connective tissues.
A. Cells
Fibroblasts
Macrophages
Structure
elongated cells with ovoid
(cigar-shaped) nuclei and
thin cytoplasm
large nucleus (often
eccentric); many surface
folds on EM
Mast cells
Function
secrete collagen, ground
substance carbohydrates,
elastin fibers
derived from monocytes;
phagocytose bacteria/cell
debris and digest them in
lysosomes
release granules in immune
response
Stain
usually only the nucleus is visible
cytoplasm stains positive w/PAS
due carbohydrate-rich enzymes in
lysosomes
large, spherical nucleus
cytoplasm stains positive w/PAS
and numerous large
due to granules of heparin and
granules
histamine
Adipocytes
small condensed nucleus
stores fat
lipid droplets lost during staining
on the side, very thin rim
of cytoplasm
* Other cells found in CT include immune cells (lymphocytes, neutrophils, eosinophils & basophils) that migrate
out from the blood.
B. Fibers (long, slender protein polymers)
Collagen
Type I
Structure
thick fibrils
bundled into
fibers
Found in
- bone, ligament, skin, tendon
- fibrocartilage, LCT, DCT
Function
resists tension
Type II
Type III
thin fibrils
fibrils do not
bundle; mesh
does not
form fibrils
hyaline & elastic cartilage
reticular fibers
resists pressure
organ framework
basement membrane
support;
filtration barrier
elastin and
fibrillin
vertebral ligaments, larynx,
elastic arteries (aorta), often
interwoven w/collagen
resists shear and
tearing
Type IV
Elastic
fibers
Stain
- pink w/H&E b/c of positively
charged amino acids
- red-brown w/silver
- yellow w/Orcein
- blue w/Mallory Azan
brown-black w/silver b/c of
glycoproteins
- pink w/H&E (so hard to
distinguish)
- black w/Orecin
C. Ground substance (gel-like substance)
1. Glycosaminoglycan (GAG)
long, unbranched polysaccharides composed of repeating disaccharide units
generally linked to a core protein
may be classified into different groups based on their chemical structure:
Histology SSN
October 12th, 2004
A. hyaluronic acid
* very large, nonsulfated molecule
* not attached directly to a core protein
* attached to the core proteins via linker proteins
B. chondroitin sulfate
* attached directly to the core protein
C. keratan sulfate
* attached directly to the core protein
2. Proteoglycans
- composed of a protein core covalently bound to many glycosaminoglycans (GAG)
A. large molecules shaped like a bottle brush
- proteoglycans may attach to hyaluronic acid, via their core proteins, to form large, complex
aggregates
- negatively-charged GAGs attract cations, which then draws in water (hydrating the ground substance)
3. Glycoproteins
- includes fibronectin & laminin
A. fibronectin – multifunctional molecule
* mediates cell adhesion to the ECM by binding to fibronectin receptors on the cells surface
* has domains for binding collagen, heparin, various cell-surface receptors, and celladhesion molecules
B. laminin – mediates interactions between epithelial cells and ECM by anchoring cell surface to
the basal lamina
HYALURONATE PROTEOGLYCAN AGGREGATE
III. TYPES OF CONNECTIVE TISSUE PROPER
A. Classification:
1. based on the proportion of cells to fibers as well as on the arrangement and type of fibers
- need to think about the following:
 cells
 fibers
 ground substance
B. loose (areolar) connective tissue
1. characteristics:
- many cells per unit volume (highly cellular)
- mostly fibroblasts
- includes many macrophages, lymphocytes, mast cells etc.
- abundant ground substance
- sparse collagen fibers (elastic, reticular)
- well vascularized (by both blood & lymph)
2. location: found beneath many epithelia (e.g. the lamina propria of GI tract)
3. specialized types:
a. adipose tissue
i. white adipose tissue – unilocular adipocytes
ii. brown adipose tissue – mutlilocular adipocytes & many mitochondria (help in heat production)
b. reticular tissue
- distinctive black appearance when stained w/silver salts
October 12th, 2004
Histology SSN
-
contains reticular fibers (type III collagen), glycoproteins & proteoglycans
provides structural support to stroma of lymph nodes, spleen, liver, bone marrow
C. dense connective tissue
1. dense irregularly arranged connective tissue (DIACT)
- fibrous tissue with fewer cells (cells are mostly fibroblasts)
- little ground substance
- collagen fibers are bundles, without definite orientation
- found in dermis, prostate, mammary glands, outer capsule of many organs
2. dense regularly arranged connective tissue (DRACT)
- made of many fibers that run in the same direction & offer resistance to stress
- little ground substance
- forms collagenous tissue & elastic tissue
a. collagenous tissue: found in tendons;
- to distinguish between CT and muscle note that CT (fibroblast) nuclei are FLATTER and
BETWEEN fibers (rather than within fibers), CT can look wavy due to the fixation process,
muscles have striated banding patterns and stain more deeply
b. elastic tissue: found in elastic ligaments of vertebral column, true vocal cords & large arteries
D. embryonic connective tissue (mesenchyme)
- characterized by many cells and few fibers
- found around developing notochord
- can differentiate into all kinds of connective tissue