Chap 40

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Large, powerful swimmers such as bluefin tuna and great white shark possess countercurrent heat exchange systems to maintain a high body core temperatures. Endothermy enables the vigorous, sustained activity that is characteristic of these animals.

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Internal temperature in the winter moth.

This infrared map shows the moth's heat distribution immediately after a flight.

Red in the thorax region indicates the highest temperature.

A countercurrent heat exchanger helps maintain a high temperature in the thorax, where the flight muscles are located, allowing the endothermic insect to fly in winter.

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Countercurrent heat exchangers. Arterial blood emerging from the body core is in close contact to the returning venous blood, and can transfer heat back to the body, thus reducing heat loss from the extremities. Countercurrent exchange allows some fish and insects to be endothermic.

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Due to the high specific heat of water, evaporation through bathing, sweating, or panting carries away body heat.

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Evolutionary convergence in fast swimmers.

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A nonliving example of negative feedback: control of room temperature.

Regulating room temperature depends on a control center that detects temperature change and activates mechanisms that reverse that change.

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Preflight warmup in the hawkmoth. The hawkmoth (Manduca sexta) uses shivering mechanism for preflight warmup of thoracic flight muscles. Once airborne, flight muscle activity maintains a high thoracic temperature.

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Radiation is the emission of electromagnetic waves and does not require direct contact to transfer heat, as when a lizard absorbs heat radiating from the sun.

Evaporation removes heat from a surface when some liquid turns to gas. Evaporation of water from a lizard’s moist surfaces has a strong cooling effect.

Convection transfers heat by the movement of fluid past a surface, as when a breeze blows across a lizard’s dry skin, or blood moves heat from the body core to the extremities.

Conduction is the direct transfer of heat by direct contact, as when a lizard sits on a hot rock.

hibernation.html: 40_22BeldingSquirrel.jpg
Body temperature and metabolism during hibernation in Belding's ground squirrels.

hypothalamus.html: 40_21HypothalamThermostat.jpg
The thermostat function of the hypothalamus in human thermoregulation.

  1. When body temperature increases, the thermostat promotes body cooling by vasodilation, sweating, or panting.
  2. When body temperature decreases, the thermostat activates warming mechanisms such as vasoconstriction, erection of fur, and shivering.

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Mammalian integumentary system. The skin and its derivatives, such as feathers, fur, or blubber, serve important functions in thermoregulation.

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Internal exchange surfaces of complex animals. The digestive , respiratory , and excretory systems all have finely branched or folded surfaces specialized for exchange.

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Cardiac (heart) muscles have striated, branched fibers. The intercalated disks contain gap junctions and provide direct electrical coupling between cells to coordinate contraction of the heart.

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Skeletal muscle are attached to bones, have striated, unbranched fibers, and are involved in voluntary movement of the body.

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Smooth muscle are located in the digestive tract, arteries, and bladder, have unstriated, spindle-shaped cells, and are involved in contraction of internal organs other than the heart.

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A neuron consists of a cell body and two or more processes called dendrites and axons. Dendrites transmit nerve impulses from their tips to the cell body. Axons transmit nerve impulses to another neuron or and effector such as muscle or gland.

sphinx_moth.html: 40_01SphinxMoth_Orchid.jpg
A sphinx moth feeding on orchid nectar.

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Contact with the environment.

  1. In a unicellular protist, such as this amoeba, the entire surface area contacts the environment.
  2. A hydra's body consists of two layers of cells. Because the aqueous environment can circulate in and out of the hydra's mouth, virtually every one of its cells directly contacts the environment and exchanges materials with it.

thermo-dragonfly.html: 40_19DragonflyThermoreg_UP.jpg
Thermoregulatory behavior in a dragonfly.

This dragonfly's “obelisk” posture is an adaptation that minimizes the amount of body surface exposed to the sun.

This posture helps reduce heat gain by radiation.

thermoregulation.html: 40_12EndoEctoThermoreg_L.jpg
The river otter is an endotherm and uses its high metabolic rate to generate heat and maintain a stable body temperature.

The largemouth bass is an ectotherm and generates little metabolic heat; its body temperature fluctuates with the water temperature.

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Tissue layers of the stomach, a digestive organ.

The wall of the stomach and other tubular organs of the digestive system has four main tissue layers.