Thermoregulation in Animals

Thermoregulation in Animals

• Animals maintain body temperature for optimal physiological performance.

• Organismal performance depends on the rate and efficiency of biochemical, physiological, and whole-body processes.

• Ectotherms obtain heat from the external environment (most fish, amphibians, and reptiles).

• Endotherms generate heat internally (birds and mammals).

Thermoregulation

• Thermoregulation in Ectotherms

  • Thermal Acclimatization: Structural or metabolic changes to adjust to varying temperatures (warm/cool seasons). This helps animals perform well in different temperatures
  • Allows animals to perform well in winter and summer
  • May involve enzyme changes or phospholipid/cholesterol level adjustments

• Thermoregulation in Endotherms

  • Maintaining a narrow body temperature range.
  • Balancing internal heat production and heat loss through the body surface

Negative Feedback: Endocrine System

• Hypothalamus: acts as a body's thermostat controlling homeostatic functions.

  • Thyroid regulates a wide variety of functions in the body.
  • Thyroid Releasing Hormone (TRH)
  • Thyroid Stimulating Hormone (TSH)
  • Triiodothyronine (T3)
  • Thyroxine (T4)
  • Iodine is crucial for thyroid hormone production.

• Low iodine intake leads to hypothyroidism

  • Thyroid cannot make T3 and T4
  • Low T3 and T4 levels despite TSH stimulation.
  • The thyroid enlarges as a response, causing goiter.

• Calcium regulation, Sodium regulation

• Negative feedback control systems.

• Examples are blood calcium level and sodium levels.

The Skin and Endothermy

• Skin is a vital organ of heat transfer.
• Blood vessels regulate heat loss by constricting or dilating (vasoconstriction/vasodilation).
• Impermeable to water, reducing heat loss from evaporation of body fluids.

Keeping Warm

• When core temperature falls below set point, hypothalamus triggers responses through the autonomic nervous system
• Immediate responses: vasoconstriction (constriction of arterioles in the skin) to reduce blood flow to the skin's capillary networks.

Examples of Keeping Warm

• Many mammals: uneven distribution of fur.
• Birds and mammals: veins and arteries positioned in legs.
• Whales and seals: adjustments in blood flow for warmth.

Keeping Cool

• When core temperature rises above set point, hypothalamus signals the autonomic system to lower body temperature
• Immediate response: vasodilation (relaxation of arterioles in skin) increases blood flow and heat loss from the body's surface.

Examples of Keeping Cool

• Birds: fly with extended legs.
• Penguins: expose featherless patches of skin.
• Elephants: dissipate heat from large ears

Structural and Behavioral Adaptations

• Adaptations for keeping warm and/or cool.
• Examples include animals shown in images.

Temperature Variations

• Temperature set point varies daily and seasonally in many birds and mammals.
• Torpor occurs during cooler conditions (lowered set point)
• Daily torpor, Seasonal torpor, Hibernation

What Happens if Core Temperature Gets Too High?

• Temporary increase in body temperature (fever), usually due to infection.
• Foreign bodies increase hypothalamus internal temperature set point
• Immune system is activated.
• Mild fever is manageable but high fever can be critical.