Page 43 - Headlines Histology2024_Neat

5) Other connective tissue cells

• They include lymphocytes, monocytes and granulocytes (especially
eosinophils and neutrophils).

II. CONNECTIVE TISSUE FIBERS
White collagenous fibers

• They are called white because they have a white color when fresh, called
collagenous because on boiling they become hydrated and yield gelatin
(glue). (Kolla=glue).

• They are destroyed with weak acids and alkalis, and digested by pepsin
and collagenase (which is an enzyme produced by the testis and some
pathogenic bacteria).

• With LM, they are arranged into wavy bundles. The bundles may
branch, but the individual fibers do not. They are acidophilic; they stain
pink with H&E; red with Van Gieson’s; green with Masson’s trichrome
stain and blue with Mallory stain.

• With EM, they are formed of bundles of microfibrils know as collagen
fibrils. The fibrils are formed of tropocollagen molecules, and they have
a characteristic periodicity repeated at 64 nm intervals.

• This periodicity is due to the unique arrangement of tropocollagen
molecules where they are arranged in end-to-end manner with each
molecule overlapping the adjacent one by one quarter of its length.

• Collagen is secreted into the intercellular matrix as tropocollagen
molecules that polymerize to form collagen of 5 different types:

Collagen type I

• It constitutes about 90% of total collagen in the body.
• It is found in fibrous connective tissue, skin tendon, ligaments and bone.
• The tropocollagen molecules are arranged to form fibers.

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