Animal Form and Function Lecture 3

The Role of Regulation and Feedback  To achieve homeostasis, most animals have regulatory systems that constantly monitor internal conditions such as temperature, blood pressure, blood pH, and blood glucose  Each variable has a set point―a normal or target value  A homeostatic system is based on three general components: 1. A sensor 2. An integrator 3. An effector The Role of Regulation and Feedback  A sensor is a structure that senses some aspect of the external or internal environment  An integrator is a component of the nervous system that evaluates the incoming sensory information and “decides” if a response is necessary to achieve homeostasis  An effector is any structure that helps restore the desired internal condition Negative Feedback  Homeostatic systems are based on negative feedback, in which effectors reduce or oppose the change in internal conditions  Examples of negative feedback – Changes in blood pH – Blood pressure – Body temperature Mechanisms of Heat Exchange All animals exchange heat with their environment in four ways: 1. Conduction 2. Convection 3. Radiation 4. Evaporation Figure 42.14 Sun RADIATION EVAPORATION Wind RADIATION CONVECTION CONDUCTION Mechanisms of Heat Exchange  Conduction is the direct transfer of heat between two physical bodies that are in contact with each other  Convection is a special case of conduction in which heat is exchanged between a solid and a liquid or gas rather than between two solids  Radiation is the transfer of heat between two bodies that are not in direct physical contact  Evaporation is the phase exchange that occurs when liquid water becomes a gas Variation in Thermoregulation  There is also a continuum regarding whether animals hold their body temperature constant  Homeotherms keep their body temperature constant  Heterotherms can tolerate changes in body temperature  Many animals lie somewhere between these extremes Variation in Thermoregulation  Many animals can control their body temperature through the process of thermoregulation, which includes – Obtaining heat – Holding the body temperature constant  An endotherm produces adequate heat to warm its own tissue  An ectotherm relies on heat gained from the environment  Humans are endothermic homeotherms Torpor vs Hibernation  Small mammals that inhabit cold climates lose heat rapidly because their surface area is large relative to their volume  To survive when temperatures are cold, species such as ground squirrels reduce their metabolic rate and allow their body temperature to drop  This response results in two possible outcomes: – Torpor—a temporary drop in body temperature – Hibernation—a longer drop in body temperature Endothermy and Ectothermy  Endotherms can warm themselves because their basal metabolic rates are extremely high – Heat given off is enough to warm the body – Mammals and birds retain this heat because they have elaborate insulating structures such as feathers or fur  Ectotherms gain heat directly from the environment and generate some heat as a by-product of metabolism – They generate a small amount of heat due to a low metabolic rate Countercurrent Heat Exchangers  Some animal structures, such as the tongue of the gray whale, conserve heat with countercurrent heat exchangers, in which arteries and veins lie beside each other – Heat flows freely from warm arteries to cool veins, allowing heat that would otherwise be lost to the surroundings to be returned to the body  Countercurrent exchangers are efficient because they maintain a gradient between the two fluids along their entire length Figure 42.17 Cross section of blood vessels of tongue (a) Tongue of gray whale Arteries are surrounded by veins in each bundle 2 mm Cold tongue Vein Artery Longitudinal section of blood vessels in tongue Artery transports blood to tongue warm cool Vein returns blood to body warm cool (b) Contrasting countercurrent with “concurrent” heat exchange Countercurrent flow: small gradients are maintained 33 32 31 30 29 28 “Concurrent” flow: large gradients disappear quickly 33 31 30 30 30 30 heat 32 31 30 29 28 27 27 29 30 30 30 30