Histology SSN
October 7, 2003
Sarah Little (sjl2017)
Grace Liu (gcl2008)
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
thin fibrils
hyaline & elastic cartilage
resists pressure
Type III
fibrils do not
bundle; mesh
does not
form fibrils
reticular fibers
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
- don’t see w/Orecin b/c brown
proteoglycans camouflage fibers
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. proteoglycans
- composed of a protein core covalently bound to glycosaminoglycans (GAG)
- negatively-charged GAGs attract cations, which then draws in water (hydrating the ground substance)
Histology SSN
October 7, 2003
2. hyaluronic acid, a GAG, attaches to the core via linker proteins
3. glycoproteins
- includes fibronectin & laminin
III. TYPES OF CONNECTIVE TISSUE PROPER
A. loose (areolar) connective tissue
1. characteristics:
- many cells per unit volume
- mostly fibroblasts
- includes many macrophages, lymphocytes, mast cells etc.
- 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
- contains reticular fibers (type III collagen), glycoproteins & proteoglycans
- provides structural support to stroma of lymph nodes, spleen, liver, bone marrow
B. dense connective tissue
1. dense irregularly arranged connective tissue (DIACT)
- fibrous tissue with fewer cells (cells are mostly fibroblasts)
- 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
- 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
C. embryonic connective tissue (mesenchyme)
- characterized by many cells and few fibers
- found around developing notochord
- can differentiate into all kinds of connective tissue
Histology SSN
October 7, 2003
CONNECTIVE TISSUE
1. This tissue contains:
a) few fibroblasts
b) macrophages, which are PAS+ because of the presence of heparin
c) macrophages, which are PAS+ because of lysosomal carbohydrates
d) a and b
e) a and c
2. This tissue contains:
I. type I collagen
II. type II collagen
III. type III collagen
IV. type IV collagen
a. III only
b. II only
c. I & III
d. I, III,& IV
3. The tissue shown is ____________ connective tissue and the extracellular matrix is secreted by _____________.
a) reticular, fibroblasts
b) reticular, smooth muscle
c) elastic, fibroblasts
d) elastic, smooth muscle
4. The tissue type shown here is specialized primarily for withstanding:
a) tearing/shear forces
b) compressive forces
c) acid secretions
d) a and b
e) none of the above
Histology SSN
October 7, 2003
ANSWERS:
1. (loose connective tissue, demonstrating macrophages – PAS stain) – C.
Loose connective tissue has many cells, which are mostly fibroblasts, and relatively little fibrous
protein. The immune cells found in LCT include macrophages, which stain positively with PAS due
to the oxidation of carbohydrates in lysosomal enzymes by periodic acid.
2. (pointer on lymph node - silver stain) – D.
Type I in the capsule, type III in reticular tissue, and type IV in basement membrane of the cells.
3. (Slide of aorta showing elastic tissue) – D.
The wall of the aorta is an example of elastic connective tissue. The elastic tissue in arteries is
secreted by smooth muscle cells, NOT fibroblasts (which secretes elastic tissue elsewhere)
4. (Slide of dense, irregular CT in dermis) - A.
Dense irregular CT is specialized for resisting tearing and shearing forces, such as those experienced by the skin on a
daily basis. Its fibers are arranged in many different directions and planes to withstand the stress from many directions.
It does not resist compression in the same way that cartilage does (type II collagen v. the type I of dense CT); however,
it is strong and can withstand a limited amount of forces and pressure.
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