Steady State and Homeostasis
- Using your own words, compare and contrast the terms homeostasis and steady state. Provide an example for each as part of your discussion.
- Using your own words, compare and contrast the terms negative feedback and positive feedback in the context of control systems. Provide an example of each.
300 words in length and includes at least 1 scholarly reference. Students are evaluated on the ability to validate, support, and provide evidence for their responses. Each student must also submit at least two classmate and the professor postings which are at least 150 words in length. The goal of classmate postings is to provide a professional, scholarly, and honest evaluation of your classmate’s content. Students are encouraged to engage in dialogue by asking pertinent questions and stating why or why not they agree with their classmates post.
Student post 1:
Homeostasis describes a sustained, relatively balanced equilibrium internally while the steady state is defined as an unaffected physiological variable. At first read, homeostasis and steady state can seem like the same thing, but they are different. Since homeostasis is a maintained level, it is generally describing a “resting” situation, or what the levels are the majority of the time. There are all different control systems and organs working in our body to help regulate and maintain our internal levels. On the other hand, steady-state does not necessarily need to be a “resting” situation, but the physiological variable stays the same. An example of this is body temperature, which regardless of what the external factors are, stays basically the same, 98.6 degrees Fahrenheit.
In our body, we have control systems that are tasked with controlling physiological variables to a constant value. Most of the time, the body control systems are described as negative feedback systems. Negative feedback means that the body wants to bring values back to homeostasis, or the body does something because something else was done to it first. An example of this is when we need more air in our lungs during exercise, the body tells us to breath faster to bring in more air. I like to think of negative feedback as reactive while positive feedback is proactive. Positive feedback increases the original stimuli to make the action occur more. A common example of positive feedback is contractions during birth. Labor contractions are a biological oscillation and a positive feedback system is used to produce regular oscillation (Maeda, 2013). This positive feedback helps the body sense how the delivery is progressing and stimulate the contractions to increase regularly until the baby is born. Negative feedback is much more common in the body than positive feedback, but they both serve their purpose in helping the body perform under stressors.
Maeda, K. (2013). Uterine contractions in normal labor developed by a positive feedback and oscillation. Health and Medical Informatics, 4(3), 4–6.
Student Post 2:
Homeostasis describes how our bodies use organs, cells, or functions to maintain a balance. We are all like gymnasts on a balance beam, making little adjustments so we don’t fall off. For example, our body wants to maintain a relatively constant amount of water to maintain hydration for functioning cells. We excrete excess water through urine, sweat, and vapor. We feel thirst when water content needs to rise. I am sure we have all experienced those hot days where we go hours without urinating because the water leaving the body is not being replaced by liquid intake quickly enough. In the winter, people may feel much less thirsty because they are not losing water at as high of a rate. Steady-state describes something within us that remains constant as much as possible. The lesson this week notes cellular activities as examples, which also makes me think about our blood volumes as sitting at a steady state. The volume remains constant regardless of activity or if the body is at rest.
Negative and positive feedback can both be used to adjust to any deviations in the desired balance. Negative feedback is used to stop whatever is causing the departure from the homeostatic state. Blood glucose control is an example of this because when sugar (glucose) levels rise, the pancreas responds with insulin in order to stop that rise (stimulus). Insulin stops secreting once the blood glucose levels have returned to the desired homeostasis. Positive feedback aims at continuing whatever the event is causing the instability. An example is blood clotting because, when we have a bleeding wound, mechanisms are activated so that platelets are sent continuously (Shibeko ,Lobanova, Panteleev & Ataullakhanov, 2010) to the site until a clot is formed. The feedback aims to continue the bleeding (stimulus) until the problem is addressed. While both types of feedback can help keep us functioning, it makes sense that negative feedback is more common because normally we have to be able to stop something adverse happening internally.
Shibeko, A. M., Lobanova, E. S., Panteleev, M. A., & Ataullakhanov, F. I. (2010). Blood Flow Controls Coagulation Onset via the Positive Feedback of Factor VII Activation by Factor Xa. BMC Systems Biology, 4(1), 5.
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