Ecotherms derive most of their derive most of their body heat from the environment rather than from their own metabolism. They have low rates of metabolism and are poorly insulated. In general, reptiles, amphibians, fishes and invertebrates are ectotherms, although few reptiles, insects and fishes can raise their internal temperature. Eclotherms tend to move about the environment and find places that minimize heat or cold stress to their bodies. Birds and Mammals are endotherms because they obtain their body heat from cellular processes. A constant source of internal heat allows them to maintain constant core temperature, despite the fluctuating environmental temperature.
Most endotherms have bodies insulated by fur or feathers or hair and relatively large amount of fat.
Homeotherms and heterotherms:
Most endotherms are homeotherms (maintain constant body temperature) and most ectoderms are heterotherms (have variable body temperature). Some endotherms vary their body temperatures seasonally (e.g. hibernation), others vary it on daily basis.
Some humming birds and mammals (e.g. shrews) can only maintain high body temperature for a body mass so small that they cannot generate enough heat to compensate for the heat lost across their large surface area. Humming birds must devote much of the day to locating and sipping nector (a very high calorie food source) as a constant energy source for metabolism. When not feeding, humming birds rapidly run out of energy unless their metabolic rates decrease considerably. At night humming birds enter a sleep like state called daily torpor and their body temperature approaches that of cooler surroundings, some bats also undergo daily torpor to conserve energy.
Osmoregulation, osmoconformer and osmoregulatory:
Excretion of nitrogenous is usually associated with the regulation of water and solute (ionic) balance by physiological process called osmoregulation. It is necessary for animals in all habitats. If the osmotic concentration of the body fluids of an animal equals that of the medium (animal’s environment) animal is an osmoregulator. When the osmotic concentration of environment changes, so does that of animals’ body fluids. This type of osmoregulation is not efficient and has limited the distribution of those animals using it. In contrast an animal that maintains its body fluids at different osmotic concentration from that of its surrounding environment is an osmoregulatory.
(45) Protonephridia:
Earliest type of nephridium to appear in the evolution of animals was protonephridium. Among the simplest of protonephridia are flame cell systems e.g. in rotifers, some annelids, larval molluscs and some flatworms. Protonephridial excretory system is composed of network of excretory canals that open to the outside of the body through excretory pores. Bulb like flame cells are located along the excretory canals. Fluid filters into flame cells from surrounding interstitial fluid and beating cilia propel the fluid through the excretory canals and out of the body through the excretory pores. Flame cell systems function primarily in eliminating excess water.
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