Internal Regulation

• Walter Cannon


  Coined the term Homeostasis in 1932
• Homeostasis


  refers to an organism’s ability to adjust its physiological processes to maintain a steady internal balance or equilibrium.
• To achieve homeostasis, regulatory systems actively defend certain values, or set points, a value that is defended by regulatory systems, such as core temperature or a particular body weight.
• The process of motivation both activates and directs behavior. When homeostasis has been compromised, the nervous system first activates behavior by generating tension and discomfort in the form of drive states such as thirst or hunger.
• ALLOSTASIS


  from the Greek roots meaning “variable” and “standing”
• ALLOSTASIS


  The adaptive way in which the body anticipates needs depending on the situation, avoiding errors rather than just correcting them
• If temperatures are too low, ice crystals form within cells and damage the cell membrane.
• In high temperatures, the proteins necessary for carrying out cell functions become unstable.
• No matter where they live, animals must maintain an internal temperature that is ideal for the normal activity of their bodies’ cells
• Extreme temperatures limit life through their impact on the chemical properties of living cells.
• Mammals and birds are referred to as endotherms due to their ability to maintain body temperature through internal metabolic activity
• endotherms


  “endon” is the Greek word for “within”
• Amphibians, reptiles, and fish are referred to as ectotherms because they rely on external factors, such as basking in the sunlight or retreating to the shade below a rock, to maintain ideal body temperature.
• ectotherms


  "ektos" is the Greek word for “outside”
• The maintenance of body temperature is influenced by an animal’s surface-to-volume ratio.
• The larger the overall volume of the body, the more heat is produced by metabolic activity.
• Within a species, populations of animals evolve features that fit a particular environmental niche.
• In cold climates, surface area and heat loss are reduced in animals that have compact, stocky bodies and short legs, tails, and ears. To promote heat loss in warm climates, animals have greater surface area in the form of slim bodies and long appendages.
• Ectotherms


  • More dependent on behavioral devices to regulate body temperature
  • Do not share endotherms' ability to use internal mechanisms for temperature regulation
• Behavioral strategies for regulating temperature

  1. Move to the right type of environment

  2. Adjust body position in response to changes in temperature

  3. Change the weight, color, and composition of fur in response to seasonal changes in temperature
• Moving to regulate temperature

  • Snakes and people stretch out in the sun when they seek additional warmth
  • Move to the shade when they need to cool off
• Adjusting body position

  • Stretch out bodies to increase surface area and lose more heat when very warm
  • Curl up to reduce exposed surface area when very cold
• Changing fur in response to temperature

  • Animals can change the weight, color, and composition of their fur
• Clothing


  • Dark, heavy clothing to absorb and maintain heat
  • Lighter clothing to reflect and dissipate heat
• Further protection from temperature changes


  Dens, burrows, nests, and other shelters
• Endothermic responses


  Responses to heat and cold
• Temperature set point


  98.6°F (37°C)
• Response to internal temperature dropping below set point

  1. Shivering

  2. Muscle twitches

  3. Teeth chattering

  4. Heat production

  5. Blood vessel constriction
• Shivering


  Muscle activity that produces heat, but at the cost of high energy expenditure
• Response to very warm temperatures

  1. Perspiration

  2. Evaporation cooling skin

  3. Panting

  4. Licking fur
• Humans have around 2.5 million sweat glands and lose an average of a liter (0.22 gallon) of sweat each day under average conditions
• Animals that do not perspire much, pant or lick their fur to produce cooling by evaporation
• Humans defend a temperature set point of 98.6°F (37°C).
• When internal temperature drops below this set point, we shiver. Shivering results from muscle twitches, which can be so intense that teeth chatter together.
• Very warm temperatures produce their own set of responses. Perspiration cools the skin through evaporation.
• Human beings have around 2.5 million sweat glands and lose an average of a liter (0.22 gallon) of sweat each day under average conditions
• Disturbances in the body’s ability to maintain the normal core temperature set point can result in the hot flashes experienced by nearly 80% of women in the months or years surrounding menopause.
• Hot flashes last seconds to minutes and are characterized by sweating, flushing, heart palpitations, and a subjective feeling of being very warm.
• very high fevers (in excess of 41°C /105.8°F) can cause brain damage
• Fevers due to illness result when chemical byproducts of bacteria or viruses, known as pyrogen, enter the brain, causing the brain to increase the core temperature set point.