Short notes on Metanephridia, Temperature regulation in fishes and Temperature regulation in Amphibians and Reptiles
Metanephridia:
Reptiles have dry skin which reduces the heat loss through evaporative cooling of the skin. They also have an expandable rib cage which allows for more powerful and efficient ventilation. Reptiles are endothermic. They have low metabolic rate and warm themselves by behavioural adaptations. Diving reptiles (sea turtles, sea snakes) conserve body heat by routing blood through circulatory shunts into the centre of the body.
It is advanced
than protonephridia (meta = beyond). Both open to the outside but metanephridia
also open internally to the body fluids and are multicellular and both are
structurally different.
Most annelids
and many invertebrates have metanephridial excretory system. In earthworm each
segment has a pair of metanephridia. It begins with a ciliated funnel, the
nephrostone that opens from the body cavity of a segment into a coiled tubule.
As beating cilia move the fluid through the tubule, a network of capillaries
surrounding the tubule reabsorbs and carries away ions. Each tubule leads to an
enlarged bladder that empties to the outside through neprhidiopore. The
excretory system of molluscs includes protonephridia is larval stage and meta
nephridia in adults.
Temperature regulation in fishes:
Temperature of
surrounding water determines the body temperature of most fishes. Fishes that
live in cold water have anti-freeze material in their blood. Poly alcohols
(e.g. sorbital, glycerol) or water soluble peptides and glycopeptides lower the
freezing point of blood plasma and other body fluids.
These fishes
also have proteins or proteins sugar compounds that stunt the growth of ice
crystals that begin to form. These fishes stay flexible and swim freely in a
super cooled. Some active fishes maintain a core temperature significantly
above the temperature of the water.
Temperature regulation in Amphibians and
Reptiles:
Amphibians and
Reptiles have air as surrounding medium and face daily and seasonal temperature
changes. Mostly they are ectotherms. Most amphibians produce little heat
metabolically and rapidly lose it. Behavioural adaptations keep their body
temperature within homeostatic range most of the time. Their moist skin can act
as a natural evaporative cooling system i.e. heat loss. It limits the habitats
and activities of amphibians to warm, moist areas. Some amphibians as bull
frogs can vary the amount of mucus they secrete from their body surface to
regulate evaporative cooling.
Reptiles have dry skin which reduces the heat loss through evaporative cooling of the skin. They also have an expandable rib cage which allows for more powerful and efficient ventilation. Reptiles are endothermic. They have low metabolic rate and warm themselves by behavioural adaptations. Diving reptiles (sea turtles, sea snakes) conserve body heat by routing blood through circulatory shunts into the centre of the body.
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