The Sensory System

Estimated Reading Time: 3 Minutes

The sensory system is a network of organs that help maintain and regulate balance in an animal’s body, whether it be temperature, gases, water, nutrition, etc. This balance is called homeostasis, where an animal is at a steady-state of internal balance. It is dynamic and constantly changing depending on external and internal factors in an animal and its environment.

One process key to homeostasis is thermoregulation, the maintenance of internal temperature in the range of tolerance for that animal depending on their environmental conditions. Most chemical, biological, and physiological processes are affected by temperature. For example, enzymes would denature if the internal temperature is at homeostasis and then proteins and other reactions could not occur, metabolic pathways could shut down.

There are two characterizations for thermoregulation in animals: ectotherms and endotherms. Ectotherms gain heat from the environment and they have a very low metabolic rate, making it need heat to speed up processes. Endotherms use metabolic heat to maintain its internal temperature. This allows these animals to be able to retain heat in colder temperatures. Both these types of exchange heat from these four processes:

  • Radiation – emission of electromagnetic waves, absorbing heat from the sun
  • Evaporation – water is emitted from the skin
  • Conduction – heat is absorbed from direct contact
  • Convection – transfer of heat by air or liquid movement on the surface

Mammals contain an integumentary system, consisting of the Epidermis, dermis, and hypodermis, which house many tissues for thermoregulation.

  • Sweat cools the body and allows heat to escape
  • Apidose tissue is used for insulation

Animals can control the flow of blood and the amount of blood in the flow. Increased blood flow in the skin is caused by vasodilation where vessels increase in diameter. Vasoconstriction reduces blood flow and therefore reduces heat transfer as vessels decrease in diameter. A countercurrent heat exchange reduces heat loss in endotherms as well as birds. Some mammals cool as well to lower body heat. Animals lose water by skin sweat, breathing, and evaporation. The water has a high specific heat, meaning it carries a lot of heat and therefore once it evaporates as water vapor, heat is also lost. This is why we sweat to cool ourselves when exercising.

Feedback mechanisms consist of a complex system. Nerve cells responsible for thermoregulation are grouped in the hypothalamus section of the brain. These nerve cells work as a thermostat and respond to temperature changes above or below the set point of homeostasis. Nerves that sense the temperature are in the skin and other body parts. Warm receptors signal the hypothalamus of heat increase and cold receptors signal decrease. When heat is below the set point in the hypothalamus inhibits loss by activating mechanisms such as vasoconstriction or hair erection, and stimulates heat-producing mechanisms like shivering. When heat is high it turns off heat-producing processes and activates cooling systems like sweating, vasodilation, and panting.

-Neil Damle

Editor at StemTalksNC


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