Physiology, Homeostasis, and Temperature Regulation 29 Physiology, Homeostasis, and Temperature Regulation

Chapter 29 Physiology, Homeostasis, and Temperature Regulation Key Concepts 29.1 Multicellular Animals Require a Stable Internal Environment 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment 29.3 Living Systems Are Temperature- Sensitive

Chapter 29 Physiology, Homeostasis, and Temperature Regulation 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature

Chapter 29 Opening Question What can ground squirrels do to lower the metabolic demands of surviving through the winter?

Concept 29.1 Multicellular Animals Require a Stable Internal Environment A stable fluid environment makes complex multicellular animals possible. Most water in an animal’s body is intracellular fluid, within the cells. The rest is the extracellular fluid, which includes blood plasma and interstitial fluid that bathes each cell. APPLY THE CONCEPT Multicellular animals have an internal environment of extracellular fluid

Figure 29.1 The Internal Environment

Organs are made up of tissues, which are then made up of cells. Concept 29.1 Multicellular Animals Require a Stable Internal Environment Homeostasis is the maintenance of stable conditions in an internal environment. Cells became specialized for maintaining the internal environment, such as temperature, pH, and ion concentration. Specialized cells evolved into tissues, organs, and physiological systems that serve specific functions. Organs are made up of tissues, which are then made up of cells.

Four types of tissue: Epithelial Connective Nervous Muscle Concept 29.1 Multicellular Animals Require a Stable Internal Environment Four types of tissue: Epithelial Connective Nervous Muscle

Some line blood vessels and hollow organs. Concept 29.1 Multicellular Animals Require a Stable Internal Environment Epithelial tissues are sheets of tightly connected epithelial cells that cover inner and outer body surfaces. Some line blood vessels and hollow organs. Some secrete substances such as hormones or sweat, or serve transport functions for nutrients. Others serve sensory functions of smell, taste, and touch.

Collagen and elastin provide strength and elasticity to cartilage. Concept 29.1 Multicellular Animals Require a Stable Internal Environment Connective tissues are dispersed cells in a secreted extracellular matrix. The composition of the matrix differentiates the types of connective tissues. Collagen and elastin provide strength and elasticity to cartilage. Bone matrix is mineralized for strength while the matrix of blood cells—plasma—is liquid. Adipose tissue, made of fat cells, has little matrix.

Nervous tissues contain two basic cell types—neurons and glial cells. Concept 29.1 Multicellular Animals Require a Stable Internal Environment Nervous tissues contain two basic cell types—neurons and glial cells. Neurons generate and conduct electrical signals, or nerve impulses, throughout the body. They are units of the central and peripheral nervous systems and communicate via chemicals, neurotransmitters. Glial cells provide support for neuronal function.

Three types of muscle tissues: Concept 29.1 Multicellular Animals Require a Stable Internal Environment Muscle tissues consist of elongated cells that generate force and cause movement. Three types of muscle tissues: Skeletal—responsible for locomotion and movement Cardiac—makes up the heart and generates heartbeat and blood flow Smooth—involved in movement and generation of forces in internal organs

Figure 29.2 Tissues Form Organs

Organs consist of multiple tissues, and most have all four types. Concept 29.1 Multicellular Animals Require a Stable Internal Environment Organs consist of multiple tissues, and most have all four types. An organ system is a group of organs that function together. To maintain homeostasis, each organ and organ system must respond to the demands of the body’s cells.

Types of information necessary for physiological systems: Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment Types of information necessary for physiological systems: Set point—a reference point Feedback information—what is happening in the system Error signal—any difference between the set point and feedback information

Figure 29.3 Control, Regulation, and Feedback

Obtain, integrate, and process information Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment Regulatory systems: Obtain, integrate, and process information Issue commands to controlled systems Contain sensors to provide feedback information that is compared to the set point

Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment Regulatory systems then issue commands to effectors that effect changes in the internal environment. Effectors are controlled systems because they are controlled by regulatory systems.

Sensory information in regulatory systems includes: Negative feedback Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment Sensory information in regulatory systems includes: Negative feedback Positive feedback Feedforward information

Increases deviation from a set point Feedforward information: Concept 29.2 Physiological Regulation Achieves Homeostasis of the Internal Environment Negative feedback: Causes effectors to counteract the influence that creates an error signal Positive feedback: Amplifies a response Increases deviation from a set point Feedforward information: Anticipates internal changes and changes the set point.

Concept 29.3 Living Systems Are Temperature-Sensitive Physiological processes are temperature- sensitive and increase their rate at higher temperatures. Q10 describes temperature-sensitivity as the quotient of the rate of a reaction at one temperature divided by the rate of the same reaction at a lower temperature. Q10 = RT/RT–10

Figure 29.4 Q10 and Reaction Rate

Concept 29.3 Living Systems Are Temperature-Sensitive Body temperature of some animals is coupled to environmental temperature. In winter, the body temperature of a fish will acclimatize to colder water. It may express more or fewer enzymes with different temperature optima.

Concept 29.3 Living Systems Are Temperature-Sensitive Thermal classification of animals can be based on source of heat. Ectotherms such as fish, amphibians, and reptiles get “heat from the outside.” Endotherms, such as birds and mammals, get “heat from the inside,” producing heat metabolically or by actively losing heat.

Figure 29.5 Ectotherms and Endotherms React Differently to Environmental Temperatures (Part 1)

Figure 29.5 Ectotherms and Endotherms React Differently to Environmental Temperatures (Part 2)

Concept 29.3 Living Systems Are Temperature-Sensitive In the thermoneutral zone the metabolic rate is low and independent of temperature. The basal metabolic rate (BMR) is the metabolic rate of a resting animal at a temperature within the thermoneutral zone. APPLY THE CONCEPT Living systems are temperature-sensitive

The heat budget equation: Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss The heat budget equation: Body temperature is the result of thermal energy flowing in from the environment and from metabolism (heatin), and thermal energy leaving the animal (heatout). If heatin does not equal heatout, body temperature will change.

Gains and losses of thermal energy occur by these mechanisms: Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Gains and losses of thermal energy occur by these mechanisms: Metabolism—conversion of ATP to do work produces heat Radiation—via infrared radiation Convection—through a surrounding medium Conduction—by direct contact Evaporation—through evaporation of water from a surface

Of central importance to the heat budget equation: Surface temperature Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Of central importance to the heat budget equation: Surface temperature Surface area These are key factors in heat loss through radiation, conduction, and convection.

Figure 29.6 Animals Exchange Heat with the Environment

Endotherms expend most of their energy pumping ions across membranes. Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Endotherms expend most of their energy pumping ions across membranes. Cells are “leakier” to ions than cells of ectotherms. Endotherms spend more energy and release more heat to maintain ion concentration gradients. LINK Review the mechanisms of ion transport described in Concepts 5.2 and 5.3

Mammals produce heat in two ways: Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss If environmental temperature (Ta) falls below an endotherm’s lower critical temperature, animal must produce heat or body temperature (Tb) will fall. Mammals produce heat in two ways: Shivering thermogenesis—skeletal muscles contract and release energy from ATP as heat. Nonshivering heat production—in adipose tissue called brown fat. See Chapter 6, p. 104

Figure 29.7 Brown Fat

The BMR per gram of tissue increases as animals get smaller. Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss The basal metabolic rate (BMR) is correlated with body size and environmental temperature. The BMR per gram of tissue increases as animals get smaller. Example: A gram of mouse tissue uses energy at a rate 20 times greater than a gram of elephant tissue.

Figure 29.8 The Mouse-to-Elephant Curve

Reducing heat loss is important in cold climates. Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Reducing heat loss is important in cold climates. Some cold-climate species have a smaller surface area than warm-climate relatives. Rounder body shapes and shorter appendages reduce surface area-to- volume ratios.

Figure 29.9 Anatomical Adaptations to Climate (Part 1)

Figure 29.9 Anatomical Adaptations to Climate (Part 2)

Other adaptations to reducing heat loss include: Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Other adaptations to reducing heat loss include: Increased thermal insulation with fur, feathers, or fat Ability to decrease blood flow to the skin by constricting blood vessels Use of countercurrent heat exchange in blood flow to appendages

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Fish produce heat metabolically in their muscles, but most heat is lost as the blood travels over the gills. In “cold” fish, cold, oxygenated blood travels from the gills to the aorta and is distributed to organs and muscles.

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss “Hot” fish have a smaller aorta and cold oxygenated blood flows instead in vessels under the skin. These vessels are close to blood vessels returning warm blood to the gills, and heat flows into the colder blood. This countercurrent heat exchanger describes the heat exchange between blood vessels carrying blood in opposite directions. LINK The principle of countercurrent exchange is seen in other physiological systems, including oxygen transport (see Concept 37.2) and the ability of the kidney to concentrate urine (see Concept 40.4)

Figure 29.10 “Cold” and “Hot” Fish (Part 1)

Figure 29.10 “Cold” and “Hot” Fish (Part 2)

Figure 29.10 “Cold” and “Hot” Fish (Part 3)

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss A rise in environmental temperature results in increased blood flow to the skin to dissipate heat. If temperature exceeds the upper critical temperature, overheating is possible. Evaporation of water through sweating or panting increases heat loss, but is an active process that also generates some heat. VIDEO 29.1 Thermographic image showing human heat radiation at rest VIDEO 29.2 Human skin flush and blood vessel dilation in response to heat VIDEO 29.3 Thermographic image showing human heat loss via sweating

Insects contract their flight muscles Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Some ectotherms are able to raise their body temperature by producing heat: Insects contract their flight muscles Honeybees regulate temperature as a group, adjusting individual heat and position in the cluster so that larvae are kept warm

Figure 29.11 Bees Keep Warm in Winter

Concept 29.4 Animals Control Body Temperature by Altering Rates of Heat Gain and Loss Both endotherms and ectotherms may use behavioral regulation to maintain body temperature. Examples: Lizard moving into sun or shade, or elephant spraying itself with water or dust

Figure 29.12 Ectotherms Can Use Behavior to Regulate Body Temperature (Part 1)

Figure 29.12 Ectotherms Can Use Behavior to Regulate Body Temperature (Part 2)

Concept 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature Hormonal and neural mechanisms control thermoregulatory adaptations, such as changes in blood vessels or shivering. The temperature regulatory system depends on feedback and acts as a thermostat. In vertebrate brains, the hypothalamus is the major center of the thermostat. The temperature of the hypothalamus can be the main feedback to the thermostat. See Figure 30.7 A

Cooling the hypothalamus can cause body temperature to rise by: Concept 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature Cooling the hypothalamus can cause body temperature to rise by: Constricting blood vessels to the skin Increasing metabolic rate Warming the hypothalamus can lower body temperature by: Dilating blood vessels to the skin Sweating or panting See Figure 30.7 A

Figure 29.13 The Hypothalmus Regulates Body Temperature (Part 1)

Other factors can change hypothalamic set points: Concept 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature The temperature of the hypothalamus is a negative feedback signal—variability from its set point can trigger thermoregulatory responses. Other factors can change hypothalamic set points: Change in skin temperature Wakefulness or sleep Circadian rhythm—a daily internal cycle ANIMATED TUTORIAL 29.1 The Hypothalamus

Fever is a an adaptive response to help fight pathogens. Concept 29.5 A Thermostat in the Brain Regulates Mammalian Body Temperature Fever is a an adaptive response to help fight pathogens. The rise in body temperature is caused by a rise in the set point for metabolic heat production. Some animals lower their temperature during inactive periods to conserve energy—daily torpor. Long-lasting regulated hypothermia— hibernation

Answer to Opening Question Ground squirrels are able to lower their metabolic demands in winter by periodically lowering body temperature. The squirrel enters its burrow when snow falls and begins a bout of hibernation for about a week. It then returns to a normal temperature for a day before entering the next bout of hibernation.

Figure 29.14 Hibernation Patterns in a Ground Squirrel