1. EXOSKELETON
By
Darbaz Ahmad
Shakar Ahmad

2. Insect Integument (Exoskeleton)
Outer epicuticle
Epicuticle
Inner epicuticle
Exocuticle
Procuticle
Endocuticle
Schmidt’s layer
Epidermis
Basement membrane
Pore canals

3. Insect Integument (Exoskeleton)
Outer epicuticle
Epicuticle
Inner epicuticle
cement
wax
oriented wax
cuticulin
Inner epicuticle
Exocuticle (procuticle)
pore canal

4. cement
Insect Integument (Exoskeleton)
wax
oriented wax
Wax Layers - Control of Water Movement
WATER
WATER
WATER IS RETAINED

5. Insect Integument (Exoskeleton)
N - acetylglucosamine polymer
O = C - CH2
H
NH
CH2OH
O
OH
H
H
H
O
H
O
H
OH
H
H
NH
O
CH2OH
O = C - CH2
n

6. Insect Integument (Exoskeleton)
O = C - CH2
NH
H
CH2OH
O
H
OH
H
H
H
O
OH
H
H
H
NH
O
CH2OH
O = C - CH2
CO
NH
NH
CO
CO
NH
CO
NH
NH
NH
CO
CO
NH
CO
CO
NH
NH
NH
CO
hydrogen bonds
CO
NH
CO
NH
CO

7. Insect Integument (Exoskeleton)
microfibril
N - acetylglucosamine polymer
sheets of microfibrils
orientation of microfibrils changes

8. Insect Integument (Exoskeleton)
Protein Matrix

9. Insect Integument (Exoskeleton)
Cross linking of protein matrix

10. Insect Integument (Exoskeleton)
Cross linking of protein matrix
OH
OH
CH2
O
OH
O
OH
Protein
CH2
N-acetyl dopamine
C
CH2
Protein
OH
CH2
CH2
OH
Protein
Protein
CH2
CH2
N-acetyl dopamine quinone

11. Insect Integument (Exoskeleton)
100000
kg/mm2
10000
1000
100
10
1
Carbon
nanotubes
Graphite fibres
Kevlar
Steel
Chitin
Tensile strength of sclerotized chitin (sclerotin)
Bone

12. Molting

13. Molting
• Arthropods periodically shed exoskeleton to
allow for growth and/or metamorphosis
• 7 steps during each molt cycle

14. 1. Apolysis
• Retraction of epidermal
cells from endocuticle
• Formation of subcuticular
space
• Molting gel secreted
• New cuticle laid down

15. 2. Epicuticle formation
• Epicuticle laid down
• It is extensively
wrinkled

16. 3. Procuticle deposition
• Formation of chitin
microfibrils
• Endocuticular layers
of old cuticle digested
• Enzymes in molting
gel initially inactive

17. 4. Ecdysis
•
Old cuticle splits along
middorsal suture
•
Cast skin = epicuticle and
exocuticle
•
Endocuticle recovered and
recycled into new procuticle

18. 5. Expansion
• Insect swallows air
• Insect swells, removes
wrinkles in epicuticle

19. 6. Hardening and darkening
• New procuticle
stabilized
• Exocuticle formed

20. 7. Endocuticle deposition
• Depositing chitin and
protein takes time
• Some insects deposit one
lamina of endocuticle
every 24 hours
Note: Ecdysis under
hormonal control