Thermoregulation

• Homeostasis


  The maintenance of a constant internal state by an organism
• Thermoregulation


  The body's ability to keep a constant body temperature
• Ectotherms


  • Their body temperature depends a lot on the outside temperature
  • Their body temperature rises and falls along with the temperature of the surrounding environment
  • They cannot increase heat production to maintain a constant internal temperature
• Endotherms


  • They can generate most of the heat they need internally
  • When it is cold, they increase their metabolic rate to produce heat
  • They do not depend on the outside temperature of the environment
  • They are able to keep a constant body temperature, no matter the outside temperature
• Endotherms have considerably higher metabolic rates than ectotherms
• Ectotherms


  They regulate their body temperature mostly through their behaviour
• Behavioural thermoregulation in ectotherms

  • Staying out in the sun when it's cold
  • Finding shade or underground burrows when it's too hot
  • Hunting at night to avoid hot temperatures
  • Changing skin colour to absorb more heat
• Endotherms also use behavioural mechanisms for thermoregulation
• Behavioural thermoregulation in endotherms

  • Elephants spraying themselves with water to cool down
  • Baby penguins huddling together to decrease heat loss
• Skin


  • It is the largest organ in the body
  • It is one of the most important structures used to keep a constant body temperature
  • It has other functions like being waterproof, protecting against microorganisms, feeling stimuli, excreting waste, and producing vitamin D

  
• Layers of the skin

  • Epidermis
  • Dermis
  • Hypodermis

  
• Epidermis


  • The outer layer of the skin, with no blood supply
  • It varies in thickness depending on body location
  • New cells are formed at the bottom layer, pushing older cells towards the surface where they die and form a layer of dead cells
  • Contains melanocytes that produce melanin to protect against UV rays

  
• Dermis


  • The layer beneath the epidermis, made up of living cells with blood capillaries
  • Contains structures involved in thermoregulation like sweat glands, sebaceous glands, sensory nerve cells, and hair follicles with erector muscles

  
• Hypodermis


  • Also known as the subcutaneous layer, made up of fat cells/adipose tissue
  • Well-supplied with blood vessels
  • Acts as an area of fat storage for energy and as an insulator against heat loss

  
• Increasing heat production


  The body increases the rate of body reactions to produce more heat
• Shivering


  Muscles contract and relax quickly, releasing heat from increased respiration
• Raising skin hairs


  Hair erector muscles contract, trapping air near the skin to provide insulation

  
• Reducing sweating


  Losing less heat by sweating less when cold
• Vasoconstriction


  Blood vessels narrow, reducing blood flow near the skin surface to decrease heat loss
• Small animals have a larger surface area to volume ratio, so they lose heat more quickly than larger animals
• Lowering skin hairs


  Hair erector muscles relax, allowing the hair to lie flat and reducing insulation
• Sweating


  Sweat is secreted and evaporates, causing evaporative cooling
• Vasodilation


  Blood vessels widen, increasing blood flow near the skin surface to allow more heat loss
• Adaptations for heat loss in hot desert animals

  • Large hairless ears full of blood vessels
  • Providing a large surface area for heat loss by radiation
• Thermoregulation


  The body's ability to keep a constant body temperature (an example of homeostasis)
• Homeostasis


  The maintenance of a constant internal state by an organism
• Examples of homeostasis


  • Constant level of glucose and oxygen in the blood
  • Constant level of water
  • Constant temperature
• If one of these factors change, the body will work to return the levels back to normal
• Ectotherms


  Cannot generate enough heat internally (ex. Fish, amphibians, reptiles)
• Endotherms


  Can generate heat internally (ex. mammals and birds)
• Endotherms have considerably higher metabolic rates than ectotherms
• Endotherms


  • They can generate most of the heat that they need internally
  • When it is cold, they increase their metabolic rate to produce heat
  • They do not depend on the outside temperature of the environment
• Ectotherms


  • Their body temperature depends a lot on the outside temperature
  • Their body temperature rises and falls along with the temperature of the surrounding environment
  • They cannot increase their heat production to maintain a constant internal temperature
• How ectotherms regulate body temperature

  1. Staying out in the sun when it is cold

  2. Finding places in the shade or digging deep underground burrows when it is too hot

  3. Hunting at night to avoid hot temperatures in the morning

  4. Changing skin colour to absorb more heat from the sun when the weather is cold
• How endotherms regulate body temperature

  1. Increasing heat production

  2. Shivering

  3. Raising skin hairs

  4. Reducing sweating

  5. Vasoconstriction
• How endotherms regulate body temperature when hot

  1. Lowering skin hairs

  2. Sweating

  3. Vasodilation
• Skin


  The largest organ in our body, one of the most important structures used to keep a constant body temperature
• Other functions of the skin

  • It is waterproof and protects the body from dehydration
  • It prevents the entry of harmful microorganisms
  • It protects us against the sun's harmful ultraviolet rays
  • It helps us feel stimuli from the outside (pain, touch, heat, cold)
  • It excretes certain waste products in sweat
  • It produces Vitamin D from the sun's energy
• Epidermis


  • The outer layer, has no blood supply
  • Varies in thickness depending on body part
  • New cells formed at bottom layer push older cells to surface
  • Bottom layer contains melanocytes that produce melanin to protect against UV rays
• Dermis


  • Found beneath epidermis, contains living cells and structures involved in thermoregulation
  • Capillaries supply skin cells and help control body temperature
  • Sweat glands produce sweat for evaporative cooling
  • Sebaceous glands produce sebum to keep skin soft
  • Sensory nerve cells sense external stimuli like temperature
  • Hair follicles produce hair, hair erector muscles contract to raise hairs