Short notes on Integumentary system of Protozoa, Cuticle and tegument in invertebrates and Amphibian skin
Integumentary system of Protozoa:
Some protozoa
have only a plasma membrane for external covering. This membrane is
structurally and chemically identical to the plasma membrane of multicellular
organisms. In protozoa plasma membrane has large surface area relative to body
volume so that gas exchange and removal of soluble wastes occur by diffusion.
This large surface area also facilitates the uptake of dissolved nutrients from
surrounding fluids. Paramecium has thick protein coat called pellicle outside
the plasma membrane. This pellicle is protective and is a semi rigid structure
that transmits force of cilia or flagella to entire body of Protozoa as it
moves.
Cuticle and tegument in invertebrates:
Some
invertebrates like rotifers have cuticles that are thin and elastic. In
crustaceans, archanids, insects, cuticles are thick and rigid and support the
body. Such cuticles consist of chitin and proteins in rigid plates that a
flexible membrane links together. Cuticles retard growth. Thus some of
invertebrates like arthropods periodically undergo molting or ecdysis. In
Cnidarians like Hydra the epidermis is only few cell layers thick. Other
cnidarians (e.g. corals) have mucous glands that secrete calcium carbonate
(CaCO3) shell. Outer covering of parasitic flukes and tapeworms in a
complex syncytuim called tegument (i.e. to cover) host enzymes cannot digest
it.
Amphibian skin:
The skin of
Amphibians consists of stratified epidermis and dermis containing mucous
glands, serous glands and pigmentation cells. Considering them physiologically
they are transitional between aquatic and terrestrial vertebrates. The earliest
amphibians were covered with dermal bone scales like their fish ancestor. The
problems faced by amphibian due to the terrestrial environments are (i)
desiccation (ii) the damage caused by ultra violet rays (iii) physical
abrasion. Evolution resulted in increased amount of Keratin production in the
inner layers of skin which napped to protect the cells from UV rays. Mucus
produced by mucus glands performs three functions (i) prevents desiccation (ii)
facilitates gas exchange and (iii) makes the body slimy. Some poison glands are
found in the dermis which produce unpleasant tasting or toxic fluid which acts
as a predator deterent. Sensory nerves penetrate the epidermis as free nerve
endings.
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