Connective Tissue II

Histology 2016-2017
Department of Anatomy &Histology: Dr.Rajaa Ali
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CONNECTIVE TISSUE II
Fibres
1. Collagen fi bres (Fig. )
_ Are composed of a protein called collagen which constitutes 30% of the dry body weight.
_ Occur singly or in bundles, e.g. tendon, aponeurosis, etc.
_ Collagen fi bres do not branch.
_ Run in a wavy course.
_ Are white in colour when fresh.
_ Each collagen fi bre consists of small parallel fi brils.
_ Under electron microscope (E/M) each fi bril consists of bundles of parallel microfi brils which show cross striations at 64 nm intervals.
_ Each microfi bril is composed of molecules of tropocollagen which are responsible for the striations.
_ Each tropocollagen is about 260 nm long and 1.5 nm thick.
_ Each tropocollagen molecule is made of three polypeptide chains called alpha units. Tropocollagen is synthesised by fi broblasts and released into the extracellular space where they get polymerised to from collagen fi brils.
_ Collagen is not only synthesised by fi broblasts but also by other cells, namely, Chondroblasts – in cartilage
Osteoblasts – in bone
Smooth muscle – in blood vessels, etc.
Odontoblasts – in the tooth
_ Collagen on denaturation (boiling) gives gelatin.
_ Though more than 25 types of collagen have been identifi ed based on their molecular composition, morphological characteristics, distribution and function, the most common types only are mentioned here. These are:
Type I – found in bones, tendons, dermis, etc.
Type II – found in cartilage
Type III – found in reticular fi bres