温血动物的进化

描述

一个恒温动物有机体新陈代谢,保持身体在一个良好的温度,主要由温暖出院的利用其内部身体机能而不是几乎完全依赖热。这样的内部产生的热量主要是动物的日常代谢的附带产品;然而条件下过度寒冷或低活动一个电热可以申请特殊的专门针对热产生的机制。无关的例子体现特殊函数肌肉劳动像发抖,aerophilous新陈代谢喜欢棕色的动物组织内。只鸟类和哺乳动物广场测量动物幸存的普遍吸热的团队。绑定lamnid鲨鱼,金枪鱼和旗鱼是吸热的。成语一样,电热广场测量描述为“温血动物”。温血动物的选择是冷血动物,虽然一般来说,没有绝对的或清晰的分离恒温动物的特性和变温动物。许多恒温动物更大数量的每个细胞线粒体不是冷血动物。这允许他们想出热量通过增加代谢脂肪和糖的速度。 Consequently, to sustain their higher metabolism, endothermic animals usually need many times the maximum amount food as poikilothermic animals do, and frequently need an additional sustained provide of metabolic fuel. In several endothermic animals, a controlled state of physiological condition conserves energy by allowing the temperature to drop nearly to close levels. Such states could also be transient, regular unit of time cycles known as torpor, or they may occur in for much longer, even seasonal, cycles known as hibernation. The body temperatures of the many little birds (e.g. Hummingbirds) and tiny mammals (e.g. Tenrecs) fall dramatically throughout daily inactivity, like nightly in diurnal animals or throughout the day in nocturnal animals, therefore reducing the energy value of maintaining temperature. Less forceful intermittent reduction in temperature additionally happens in alternative, larger endotherms; as an example human metabolism additionally slows down throughout sleep, inflicting a call core temperature, normally of the order of one degree Centigrade. There could also be alternative variations in temperature, typically smaller, either endogenous or in response to external circumstances or vigorous labor, and either a rise or a drop. The resting organic structure generates concerning simple fraction of its heat through metabolism in internal organs within the thorax and abdomen, similarly as within the brain. The brain generates concerning 16 PF of the entire heat made by the body. Heat loss could be a major threat to smaller creatures, as they need a bigger quantitative relation of expanse to volume.Little homothermic animals has insulation within the type of fur or feathers. Aquatic homothermic animals, like seals, usually have deep layers of blubber below the skin and any coat that they may have; each contribute to their insulation. Penguins have each feathers and blubber. Sphenisciform seabird’s feathers square measure scale-like and serve each for insulation and for streamlining. Endotherms that sleep in terribly cold circumstances or conditions predisposing to heat loss, like polar waters, tend to own specialized structures of blood vessels in their extremities that act as heat exchangers. The veins square measure adjacent to the arteries jam-packed with heat blood. A number of the blood vessel heat is conducted to the cold blood and recycled into the trunk. Birds, particularly waders, usually have terribly well-developed heat exchange mechanisms within their legs—those in the legs of emperor penguins square measure a part of the diversifications that alter them to pay months on Antarctic winter ice. In response to cold several homothermic animals additionally scale back blood flow to the skin by constriction to cut back heat loss.