Homeothermy and temperature regulation

Why is body temperature (T) important? Relationship between metabolic enzymes and temperature

  1. Definitions

    1. Ectothermy: Internal heat sources are small; body T largely dependent on external sources of heat
    2. Endothermy: Internal heat sources are a significant determinant of body T
    3. Homeothermy: The ability to maintain a steady body T that is independent of environmental (ambient) T
      Endothermy and homeothermy are distinct concepts (see Fig. 1), but they are tightly linked in mammals. Homeothermic endotherms defend a temperature "set point" (metabolic thermoregulation).

  1. Costs and benefits of homeothermy

    1. Benefits

      1. Faster diffusion (greater biochemical efficiency)
      2. More rapid cellular resposes (e.g., neurons)
      3. More rapid and stronger muscle contractions
      4. Ability to be active in otherwise inhospitable environments (e.g., polar regions)
      5. Freedom from dependence on sunlight to regulate body T
      6. Allow for coordination of biochemical processes, since they're all optimized to operate in the same range of temperatures. This in turn enables a more complex physiology.
      7. Increased ability to sustain a high level of activity

    1. Costs

      1. Increased energy requirements (roughly an order of magnitude higher at room temperature)
        • Greater risk of starvation
        • Fewer resources to devote to growth and reproduction
      2. Increased evaporative water loss because of higher respiratory rate
      3. Increased susceptibility to thermal stress - because enzymes have evolved to operate within a narrow range of temperatures

  1. How is body T maintained ( thermoregulation )?
    1. Behavioral thermoregulation
    2. Metabolic thermoregulation

    1. Environmental heat loss/gain

Tactics used to retain heat
  1. Hair
  2. Blubber
  3. Shivering
  4. Blood vessel specializations ( regional heterothermy)

    1. counter-current heat exchange
    2. vasoconstriction
    3. Heat map showing regional heterothermy associated with vasoconstriction
    4. Dolphin appendages showing a combination of vasoconstriction and counter-current heat exchange to thermoregulate

  5. Big body size
  6. Huddling (if with others) or curling up (if alone)
  7. Nest building
Tactics used to dissipate heat or minimize heat gain
  1. Evaporation
    1. Sweating
    2. Panting (respiratory vapor)
  1. vasodilation of peripheral blood vessels in combination with large ears
  1. Behavioral thermoregulationEmbed from Getty Images
  2. Hair

  1. Characteristics of endothermy (suggested reading)

    1. Thermoneutral zone (TNZ): The range of temperatures at which no extra energy is required to maintain homeothermy.

    1. Lower critical temperature (LCT): The lower temperature threshhold at which the animal has to increase its metabolism to maintain body temperature.

    1. Upper critical temperature (UCT) The upper temperature threshhold at which the animal has to increase its metabolism to cool the body.

    Homeothermy worksheet #1

  1. Special temperature regulation strategies:

    1. Hypothermia

      1. Benefits
      2. Can be daily, seasonal
      3. Examples: hedgehogs, some bats, some primates, carnivores, rodents
      4. Characteristics of the hypothermic state

        1. Shivering is suppressed
        2. Body T falls to within a few degrees of ambient T (unless ambient T falls below freezing)
        3. Metabolic rate decreases, leading to
          • Reduced respiration rate
          • Reduced heart rate

      1. Warming back up

        1. Metabolism of brown fat
        2. Shivering

      2. Hypothermia occurs in bouts (see Fig. 1), with interspersed warming periods

    Why might they periodically warm up during hibernation?

    1. Heat loading

Basic skeletal anatomy

Skeletal structure

  1. Basic parts
    1. Skull=cranium + mandible
    2. Postcranial skeleton=axial skeleton + appendicular skeleton

  2. Skull
    1. Landmarks
      1. Foramen magnum
      2. Rostrum
      3. Turbinal bones (AKA turbinates)
      4. External auditory meatus
      5. Auditory bullae
      6. Maxilla
      7. Mandible
      8. Zygomatic arch
      9. Sagittal crest


  3. Axial skeleton (shown in pink)
    1. Vertebrae
    2. Ribs

  4. Appendicular skeleton
    1. Pectoral girdle + forelimbs + manus + pollex + phalanges
    2. Pelvic girdle + hindlimbs + pes + hallux + phalanges

Structures associated with homeothermy (*diagnostic)

  1. Skeletal features
    1. Single bone in mandible*
    2. Squamosal-dentary articulation*
    3. Heterodont, diphyodont dentition

  2. Soft tissues
    1. Hair*
      1. Anatomy (See also Fig 6.2)
      2. Functions (insulation, protection, communication)
      3. Types (based on function and how they grow: definitive vs. angora)
      4. Color patterns
      5. Pigments
      6. Moulting and hair replacement

    2. Glands associated with hair
      1. Sebaceous glands*
      2. Sweat glands* (not all mammals)

    3. Muscular diaphragm*

      • Associated with the loss of lumbar ribs
      • Allows abdominal organs to be displaced outwards as thoracic cavity expands

    4. Four-chambered heart with left aortic arch*

    5. Enucleate erythrocytes*
      colored scanning electron micrograph

Homeothermy worksheet #2

Dentition and feeding

I. Teeth

  1. Heterodont dentition
    1. Incisors: cutting, gathering food
    2. Canines: capturing food, communication displays
    3. Premolars: grinding or slicing
    4. Molars: grinding or slicing
    5. Premolars + molars often hard to differentiate, so referred to as "cheek teeth"
  1. Tooth structure
    1. crown
    2. root
    3. enamel
    4. dentine
    5. pulp cavity
    6. cementum

  2. Tooth growth
    1. closed-rooted
    2. open-rooted (ever-growing)

  3. Tooth replacement
    1. Deciduous (milk) teeth
    2. Horizontal vs. vertical replacement

  4. Occlusal surfaces
  5. Variations on the basic pattern
    1. Homodont dentition
    2. Edentate
    3. Tusks
    4. Diastema

  6. Dental formulae (e.g., 3/3, 1/1, 4/3, 1/1)

II. Foods and Feeding

  1. Anatomy of the digestive system
  2. Modes of foraging
    1. Insectivory
      1. aerial
      2. terrestrial
      3. myrmecophagy (ant-eating; see first minute or so of video)

    2. Carnivory
      1. terrestrial
      2. aquatic
      3. sanguinivory (blood feeding; see video starting at about 1:00)

    3. Herbivory
      1. ruminants
      2. hind gut fermenters
      3. granivory (chipmunk stuffing cheek pouches with seeds; start at 1:05)
      4. folivory
      5. frugivory
      6. nectivory
      7. gummivory

    4. Filter feeding
    5. Omnivory

  3. Anatomical specializations associated with different modes of foraging
    Mode of foraging Teeth Tongue Stomach Intestines Cecum
    Insectivory numerous, spiky, incisors procumbent
    Example: mole
    Example: shrew
    -- simple short mostly lacking
    Myrmecophagy absent or reduced in numbers, peg-like
    Example: tamandua anteater
    extremely long simple, often roughened short small or lacking
    Terrestrial carnivory sharp incisors; long, conical canines; often carnassial cheek teeth; may have crushing molars
    Example: dog
    -- simple short small
    Aquatic carnivory homodont, spiky, numerous
    Example: common dolphin
    -- simple or multichambered (cetaceans only) variable small or absent
    Sanguinivory very sharp upper incisors; reduced cheek teeth
    Example: vampire bat
    grooved tubular, highly extensible long small or lacking
    Herbivory (except nectivores) incisors robust or absent; canines reduced or absent; diastema; cheek teeth enlarged with complex occlusal surfaces
    Example: beaver
    -- simple (hindgut fermenters) or multichambered (ruminants) long large
    Filter feeding none (baleen)
    Example: grey whale
    -- multichambered -- present (for digesting chitin)
    Omnivory sharp incisors and canines; flat cheek teeth with rounded cusps
    Example: bear
    -- simple long small