Do you ever wonder why you sweat on a warm day, but shiver on a cold one? Do you find it interesting that you feel thirsty after going a while without water? To most people, it is intuitive that you sweat when you are trying to cool off, and you experience the sensation of thirst when you are dehydrated, but why? What processes are happening so that you experience these sensations? Your body works hard to ensure that its internal environment is perfect for all your organs to work efficiently, and this steady state is maintained by a culmination of response mechanisms broadly referred to as homeostasis.
Definition
Homeostasis is defined by the processes that allow for an organism to maintain optimal steady state conditions. In simpler terms, it allows for the perfect balance of water, nutrients, electrolytes, and acids and bases to be maintained even when external conditions change, or nutrients and water are exhausted. This phenomenon is not exclusively present in humans! All living organisms require some level of homeostasis to be able to respond to an ever-changing environment.
Homeostasis in Plant Life
Though there are many complex ways that plants maintain a balanced internal environment as their habitat changes, one of the cooler representations of plant homeostasis can be seen in response to changing light sources. If you place your favorite house plant in a place where sunlight is on the left, homeostasis signals to the plant to grow towards the light, resulting in a left leaning plant! Due to photosynthesis (the process of turning carbon dioxide into sugar using light energy) sunlight is essential to maintaining perfect internal conditions for plant growth. Therefore, the change in shape and position of the plant, called phototropism, occurs so that the organism can absorb more sunlight. This is one very effective way that the organism to responds to its environment and maintains balance.
Homeostasis in the Human Body
Earlier in the article we mentioned shivering and sweating, both ways that the body maintains an internal temperature of approximately 98 degrees Fahrenheit. We also mentioned thirst, the way that the body makes sure that we are properly hydrated, and if not, feel the need to seek out water. These mechanisms require closely regulated pathways involving your nervous system, but in principle are quite simple. There are receptors located throughout the body that sense changes in temperature and cause the sweat or shiver response (amongst others), to bring your body temperature back to an optimal temperature around 98 degrees. In specific cases, such as a cold, your body needs to be a little warmer to help your immune system fight infection. This is causes you to shiver, which are tiny rhythmic muscle contractions that help produce heat, causing your body temperature to increase, and causes feeling of “chills” when you are sick.
Your body regulates water levels largely through changes in blood pressure, as your blood contains a significant portion of the water in the body, and slight changes in blood pressure can indicate systemic changes in hydration. Your kidneys are the main site of water homeostasis (you can think of this as water balance) and respond by increasing or decreasing urine output due to increased or decreased blood pressure respectively. The kidneys also respond to increased solute in the blood through receptors that are present in the brain. Like decreased blood pressure, too much salt, protein and/or sugar concentration in the blood will stimulate a decrease in urine output and increase the feeling of thirst. This is why a salty meal can make you feel as though you need to drink more water, even when you are drinking plenty!
See this earlier post on osmosis and diffusion for a more thorough explanation of solutes, concentrations, and the movement of water in the body.
What happens when homeostasis does not work? What can we do to help?
Temperature, acid/base balance, water, and sugar are some of the main conditions that need to remain in a specific range to support life. Both in plants as well as mammals, if any of these components fall out of balance, there can be severe consequences. A common condition where the body can no longer maintain proper balance is diabetes. In both type I and type II diabetes, the body is unable to maintain sugar homeostasis, causing sharp increases and decreases in blood sugar. This can cause a variety of symptom, so individuals with this condition are given insulin to help restore proper sugar balance. Interventions and treatments such as these are life changing, and it is important to continue studying how the body achieves homeostasis to improve the health and wellbeing of all!
Author: Sydni Britton