Biology Today - February 2018

(Michael S) #1
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
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