Chapter 40 (3)

__ is the process by which animals maintain an internal temp within a tolerable range. __ is critical to survival because most biochemical and physiological processes are very sensitive to changes in body temp. Membranes can also change properties, becoming increasingly fluid or rigid as temps rise or fall, respectively.

Internal metabolism and the external environment provide the sources of heat for __. Birds and mammals are mainly __, meaning that they are warmed mostly by heat generated by metabolism.

A few nonavian reptiles, some fishes, and many insect species are also mainly __. In contrast, amphibians, lizards, snakes, turtles, many fishes and most invertebrates are mainly __, meaning that they gain most of their heat from external sources.

Animals that are mainly __ are known as __; those that are mainly __ are __.

__ animals can maintain stable body temperatures even in teh face of large environmental temperature fluctuations.
e.g. cold winter and these types of animals

In a cold environment, an __ generates enough heat to keep its body substantially warmer than its surroundings. In a hot environment, __ have mechanisms for cooling the body, enabling them to withstand heat loads that are intolerable for most __.

because their heat source is largely enivornmental, __ generally need to comnsume much elss food than __ of equivalent size- an advatage if food is unavailable. __ also usually tolerate larger fluctuations their internal temps. Although __ do not generate enough heat for __, many adjst body temp by behavioral means, like seeking out shade or basking in sun. Overall, __ is an effective and successful strategy in most environments.

Animals can have either a variable or a constant body temperature An animal wose body temp varies with its environment is called a __. In contrast a __ has a relatively constant body temp.

Fromt eh descriptions of __ and __, it might seem that all __ are __ and all __ are __. Actually, there is no fixed relationship between teh source of heat and the stability of body temp.

It is a common misconception that __ are "cold-blooded" and __ are "__". __ don not necessarily have low body temps. In fact, when sitting in the sun, many __ lizards have higher body temps than mammals. Thus the terms __ and__ are misleading.

__ depends on an animal's ability to control the exchange of heat with its environment. ANy organism, like any object, exchanges heat by four physical processes: __, __, __ and __. heat is always trasferreded to an object of __ temp to one of __ temp.

the essence of __ is maintaining rates of heat gain that equal rates of heat loss. Animals do this thorguh mechanisms that either reduce heat exchange overall or taht favor heat exchange in a particular direction.

In mammals, several of tehse mechanisms involve the __, teh outer covering of the body, consisiting of skin, hair and nails. A key organ of this system is the __, which consists of the __, which is the outermost layer of skin and is composed mostly of dead epithelial cells taht continually flake and fall off- and teh __, whcih contains hair follicles, oil and sweat glands, muslces, nerves, and blood vessels. Beneath the skin lies the __, a layer of adipose tissue tha tincludes fat-storing cells as well as blood vessels.

A major thermoregulatory adaptation in mammals and birds is __, which reduces the flow of heat between an animal and its environment. Sources of _- include hair, feathers and layers of fat formed by adipose tissue.

Many animals that rely on __ to reduce voverall heat exchange also adjust their insulating layers to help __.
- lad mammals/ bird: cold- raising fur or feathers
--- this traps a thicker layer of air, thereby increasing the insulating power of the fur or feather layer.
- to repel water that would reduce the insulating capacity of feathers or fur, some animals secrete oily substances, like oils that birds apply to feathers during preening.
- humans rely on fat for insulation. (goosebumps)

__ plays a particularly important role in ___ by marine mammals, like whales and walruses. Just under the skin, marine mammals have a very thick layer of insulating fat called __. This insulation __ provides is so effective that marine mammals maintain body core treps of about 36-38^oC withough requiring much more food energy than land mammals of similar size.

__ provide a major route for heat flow between the interior and exterior of the body. Adaptations tha tregulate the extent of blood flow near the body surface or taht trap heat within the body core play a significant role in __.

In response to changes int eh themperature of their surroundings, many animals alter the amount of blood flowing between their body core and their skin. Nerve signals that relax the muscles of the vessel walls result in __, an increase in teh diameter of superficial blood vessels (those near the body surface). As a consequence of the increase in vessel diameter, blood flow in the skin is elevated. In endotherms, __ usually warms teh skin and incraeses the transfer of body heat to the environment by __, __ and __.

The reverse process, __ reduces blood flow and heat transfer by decreasing hte diameter of superficial vessles.

Like __, some __ control heat exchange by regulating blood flow.

In many birds and mammals, reduction of heat loss relies on __, the flow of adjaent fluids in opposing directions that maximizes transfer rates of heat or solutes. Heat transfer involves an antiparallel arrangement of blood vessels called a __. When tisseus are organized this way, arteries and veins are located adjacent to each other.

As warm blood passes through arteries, it transfers heat to the colder blood returning from the extremities in the veins. Because the arteries and veins have __- blood flowing in opposite directions- heat transfer occurs along the entire length of the exchanger.

In controlling heat gain and loss, some species regulate the extent of blood flow to the __. by allowing blood to pass through the heat exchanger or diverting it to other blood vessels, these animals alter the rate of heat loss as their physiological state or environment changes. In other species, the __ mechanism can be "shut down" allowing muscle-produced heat to be lost from teh thorax to the abdomentand then to the environment

Many mammals and birds live in palces where thermoregulation requires cooling as wella s __. If environmental temp is above body temp, animals gain heat fromt eh environment as well as from metabolism, and __ is teh onyl way to kep body temp from rising rapidly. Terrestrial animals lose water by __ across teh skin and when they breathe. Water absorbs considerable heat when it evaporates; this heat is carried away fromt ehbody surface with the water vapor.

__ in some animals is aided by adaptations that cn greatly augment this cooling effect. __ is important in birds and many mammals. Some birds have a pouch richly supplied with blood vessels int ehfloor of the mouth; fluttering the pouch increases evaporation. Many terrestrial mammals have sweat glands controlled by the nervous system.

Both __ and __ control body temp through behavoiral responses.
many __ maintain a newarly constant body temp through relatively simple behaviors. More extreme behavioral adaptations in some animals include hibernation or migration to a more suitable climate.

All amphibians and most reptiles other than birds are __ and control body temp mainly by __. When exposed to air, most amphibians lose heat rapidly by __ fromt heir moist body surfaes, making it difficult to keep sufficiently warm. However, an amphibian can maintain a satisfactory body temp simply by moving to a location where solar heat is available. When the surroundings are too warm, amphibians seek shady spots or other cooler microenvironments.

Like amphibioans, reptiles other than bireds use __ as their dominant means of __. When cold, they seek warm places, orienting themselves toward heat sources and expading the portion of their body surface exposed to the heat source. When hot, they move to cool areas or turn in another direction. Many reptiles keep their body temps very stable over teh course of a day by shuttlign back and forth between warm and cool spots.

Many terrestrial invertebrates can adjust internal temp by the same behaviroal mechanisms used by vertebrate __.

Honeybees use a __ mechanism that depends on social behavior. In cold: incrase heat by huddling together- retain heat. They maintain ar elatively constant tep by changing how densely they huddle. Individuals move between teh cooler outer edges of the cluster and the warmer center, thus circulating and distributing hte heat. Even when huddling, they must expend considerable energy to keep warm during long periods of cold waer, and this is the main function of storing large quantities of fuel in the hive in teh form of honey.

Honeybees also control the temp of the hive by transporting water to the hive in hot weather and fanning with wings, promoting __ and __. Thus, a colony of hneybees uses many mechanisms of __ seen in other organisms.

Because __ generally maintain body temps considerably higher than that of the environment, they must counteract constant heat loss. __ cna vary heat production to match changig rates of heat loss. Heat production-__- is increased by such muscle activity as moving or shivering. In some mammals, certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP. THis __ takes place throughout the body, but some mammals have a tissue called __ int he neck adn between teh shoulders that is specialized for rapid heat production. Through shivering and nonshivering__, mammals and birds in cold environments can increase their metabolic heat production by as much as five to ten times the levels that occur in warm conditions.

Many species of flying insects are _- the smallest of all endotherms. THe capacity of such __ insects to elevate body temp depends on powerful flight muschles, which generate large amounts of heat when operating. Many __ insects warm up by shivering before taking off. As they contract their flight muscles in __, only slight wing movements occur, but considerable heat is produced. Chem reactins, and hence __, speed up in teh warmed up flight "motors" enabling these insects to fly even on cold days or at night.

__ contributes to thermoregulation across many animal species. In birds and mammals, __ to seasonal temp changes often includes adjusting the amount of insulation- by growing a thicker coat of fur int eh winter and shedding it in the summer, for example. THese changes help endotherms keep a constant body temp throughout the year.

__ in ectotherms often includes adjustments at the cellular level. Cells may produce variatns of enzymes that have the same function but different optimal temps. Also, proportions of saturated and unsaturated lipids in membranes may change; unsaturated= more fluid

Some ectotherms that experience subzero body temps protect themselves by producing "__" compounds that prevent ice formation int eh cells.

The regulation of body temp in humans and other mammals is brought about by a complex system based on __ mechanisms. The sensors for __ are concentrated in a brain region called __

The __ contains a group of nerve cells that functions as a thermostat, responding to body temps outside a normal range by activating mechanisms taht promote heat loss or gain. Warm receptors signal teh __ thermostat when temperatures increase; cold receptors signal when temperatures decrease.

At body temps. below the normal range, the thermostat inhibits heat loss mechanisms and activates heat-saving ones such as the constriction of certain blood vessels and the raising of fur, while stimulating heat-generating mechaninsms (__ and __). Inr esponse to elevated body temp, the thermostat shuts down heat retention mechanisms and promotes body cooling by __,__ or __. Because the same blood vessel supplies the __ and ears, an ear thermometer records the temp detected by the __ thermostat.

In the course of certain bacterial and viral infections, mammals and birds develop fever, an elevated body temp. A variety of experiments have shown that fever reflects an increase in teh __ for the biological thermostat.

Although only endotherms develop __, lizards exhibit a related response. When infected with certain bacteria, the iguana seeks a warmer environment and then maintains a body temp that is elevated by 2-4 degrees C. Similar observations in fishes, amphibians, and even cockroaches indicate broad evolutioanry conservatio of this resposne of certain infectsion.