Concept 29.1 Multicellular Animals Require a Stable Internal Environment

• Multicellular animals provide for the needs of all of their cells by maintaining a stable internal environment, which consists of the extracellular fluid. Review Figure 29.1
   
• Tissues are assemblages of cells. Although there are many cell types, there are only four types of tissues: epithelial, muscle, connective, and nervous. Review WEB ACTIVITY 29.1
   
• Organs are made up of tissues; most organs contain all four tissue types. Organs are grouped into organ systems. Review Figure 29.2
   

Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment

• Physiological systems are regulated primarily through negative feedback, which keeps the system stable by returning it toward a set point.
   
• Positive feedback increases the deviation from a set point. Feedforward information changes a system's set point. Review Figure 29.3
   

Concept 29.3 Living Systems Are Temperature-Sensitive

• Life is sustained within a narrow range of ambient (environmental) temperatures. Q₁₀ is a measure of the sensitivity of a life process to temperature. Review Figure 29.4
   
• An animal's metabolic rate (MR) is a measure of the energy turnover of its cells. The MR is often measured in terms of the rate of O₂ consumption.
   
• The body temperature of an ectotherm depends on heat from the environment.
   
• Endotherms regulate body temperature independent of the environment by metabolically producing heat internally.
   
• The minimal metabolic rate at which an endotherm can maintain homeostasis of its internal environment in a resting state is its basal metabolic rate (BMR). Review Figure 29.5 and WEB ACTIVITY 29.2
   

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss

• A heat budget describes all pathways for heat exchange between an organism and its environment. These avenues of heat exchange are metabolism, radiation, convection, conduction, and evaporation. Review Figure 29.6
   
• The BMRs of endothermic animals are higher than the resting metabolic rates of ectotherms when at the same body temperature.
   
• The basal metabolic rate is a function of body size. Review Figure 29.8
   
• Surface insulation decreases heat loss.
   
• Adaptations such as countercurrent heat exchange can conserve metabolic heat. Review Figure 29.10
   
• Behavioral thermoregulation is the first line of defense against changes in the thermal environment. Review Figure 29.11
   
• Evaporative water loss is an effective but expensive means of heat loss.
   

Concept 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature

• In mammals, the control of thermoregulatory effectors relies on commands from a regulatory center in the hypothalamus of the brain.
   
• The hypothalamus uses its own temperature as a negative feedback signal and external (skin) temperature as a feedforward signal. Review Figure 29.13, WORKING WITH DATA 29.1, and ANIMATED TUTORIAL 29.1
   
• Fever is a regulated increase in body temperature. Hibernation is a regulated decrease. Review Figure 29.14