Physiology, Homeostasis, and Temperature Regulation

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Physiology, Homeostasis, and Temperature
Regulation
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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

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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

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Chapter 29 Opening Question

• What can ground squirrels do to lower the
  metabolic demands of surviving through the winter?

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Concept 29.1 Multicellular Animals Require a
Stable Internal Environment

• A stable fluid environment makes complex
  multicellular animals possible.
• Most water in an animals body is intracellular
  fluid, within the cells.
• The rest is the extracellular fluid, which
  includes blood plasma and interstitial fluid that
  bathes each cell.

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Figure 29.1 The Internal Environment
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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.

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Concept 29.1 Multicellular Animals Require a
Stable Internal Environment

• Four types of tissue
• Epithelial
• Connective
• Nervous
• Muscle

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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.

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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 cellsplasmais liquid.
• Adipose tissue, made of fat cells, has little
  matrix.

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Concept 29.1 Multicellular Animals Require a
Stable Internal Environment

• Nervous tissues contain two basic cell
  typesneurons 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.

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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
• Skeletalresponsible for locomotion and movement
• Cardiacmakes up the heart and generates
  heartbeat and blood flow
• Smoothinvolved in movement and generation of
  forces in internal organs

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Figure 29.2 Tissues Form Organs
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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 bodys
  cells.

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Concept 29.2 Physiological Regulation Achieves
Homeostasis of the Internal Environment

• Types of information necessary for physiological
  systems
• Set pointa reference point
• Feedback informationwhat is happening in the
  system
• Error signalany difference between the set point
  and feedback information

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Figure 29.3 Control, Regulation, and Feedback
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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

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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.

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Concept 29.2 Physiological Regulation Achieves
Homeostasis of the Internal Environment

• Sensory information in regulatory systems
  includes
• Negative feedback
• Positive feedback
• Feedforward information

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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.

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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/RT10

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Figure 29.4 Q10 and Reaction Rate
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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.

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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.

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Figure 29.5 Ectotherms and Endotherms React
Differently to Environmental Temperatures (Part 1)
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Figure 29.5 Ectotherms and Endotherms React
Differently to Environmental Temperatures (Part 2)
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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.

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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.

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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
• Metabolismconversion of ATP to do work produces
  heat
• Radiationvia infrared radiation
• Convectionthrough a surrounding medium
• Conductionby direct contact
• Evaporationthrough evaporation of water from a
  surface

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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.

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Figure 29.6 Animals Exchange Heat with the
Environment
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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.

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

• If environmental temperature (Ta) falls below an
  endotherms lower critical temperature, animal
  must produce heat or body temperature (Tb) will
  fall.
• Mammals produce heat in two ways
• Shivering thermogenesisskeletal muscles contract
  and release energy from ATP as heat.
• Nonshivering heat productionin adipose tissue
  called brown fat.

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Figure 29.7 Brown Fat
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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.

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Figure 29.8 The Mouse-to-Elephant Curve
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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.

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Figure 29.9 Anatomical Adaptations to Climate
(Part 1)
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Figure 29.9 Anatomical Adaptations to Climate
(Part 2)
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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

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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.

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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.

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Figure 29.10 Cold and Hot Fish (Part 1)
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Figure 29.10 Cold and Hot Fish (Part 2)
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Figure 29.10 Cold and Hot Fish (Part 3)
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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.

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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

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Figure 29.11 Bees Keep Warm in Winter
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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

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Figure 29.12 Ectotherms Can Use Behavior to
Regulate Body Temperature (Part 1)
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Figure 29.12 Ectotherms Can Use Behavior to
Regulate Body Temperature (Part 2)
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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.

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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

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Figure 29.13 The Hypothalmus Regulates Body
Temperature (Part 1)
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Concept 29.5 A Thermostat in the Brain Regulates
Mammalian Body Temperature

• The temperature of the hypothalamus is a negative
  feedback signalvariability from its set point
  can trigger thermoregulatory responses.
• Other factors can change hypothalamic set points
• Change in skin temperature
• Wakefulness or sleep
• Circadian rhythma daily internal cycle

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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 energydaily torpor.
• Long-lasting regulated hypothermia hibernation

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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.

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Figure 29.14 Hibernation Patterns in a Ground
Squirrel