Biology Today - February 2018

Excretion Exchange of gases Sensation Conduction of fluids

Functions of Epithelial Tissues

Protection Formation of exoskeleton Secretion and absorption

CONNECTIVE TISSUE

It is formed from mesoderm of the embryo and is the most abundant and widely distributed tissue of the body.

This tissue provides the structural framework and support to different tissues and helps in body defence, repair, fat storage, etc.

Components of Connective Tissues

There are three components present in the connective tissue, namely, matrix (ground substance), cells (fixed and wandering) and fibres.

Fibres

• Reticular fibres are delicate, branched
  and inelastic, made up of reticulin
  protein. They always form a network. Most
  abundant in lymph nodes, bone marrow
  and spleen.
  
  
  • Collagen fibres are thick, unbranched,
    long, wavy and often form bundles. They are
    very tough and inelastic, resist stretching
    and are made up of collagen protein. Most
    abundant in tendons.
    
    
    • Elastic fibres are slender, branched and
      straight. They recoil to their original length
      after stretching or distortion. They are formed
      of elastin protein and are most abundant in
      ligaments.
    
    
    
    
  
  
  
  

Red blood cell in vessel

• Matrix fills the spaces between cells and
  surrounds connective tissue fibres. It is clear,
  colourless and viscous. It is mainly a mixture
  of carbohydrates and proteins.

Fixed cells

• Chromatophore-Pigment
  cell in the dermis of skin which
  imparts colour.


• A fixed macrophage is a
  phagocytic cell that engulfs
  cell debris and pathogens.


• Mast cell stimulates local
  inflammation by producing
  histamine, heparin and
  serotonin.


• Fibroblast produces fibres
  and matrix.


• Adipocyte (fat cell) stores
  fat.

Wandering cells

• A plasma cell is an active, mobile
  immune cell that produces antibodies.


• Free macrophage is wandering,
  phagocytic cell that patrols the tissue,
  engulfing debris and pathogens.


• Mesenchymal cell gives rise to different
  types of connective tissue cells.


• Neutrophil is small, mobile, phagocytic
  blood cell that enters tissues during
  infection or injury.


• Lymphocyte ingests cell debris,
  bacteria and foreign particles.

Fig.: Connective tissue components

Types of Connective Tissue
Connective tissue can be classified into three types as shown in the flow chart given below:

Connective Tissue

Loose connective tissue Dense connective tissue Specialised connective tissue

Areolar tissue Adipose tissue Dense regular

connective tissue

Dense irregular

connective tissue

Reticular tissue

Compact

Hyaline cartilage Fibrous cartilage Calcified cartilage

Spongy

White fibrocartilage Yellow elastic fibrocartilage

Yellow elastic connective tissue

Sheet Sheet

White fibrous connective tissue

Cord (Tendon) Cord (Ligament)

Cartilage Bone Blood