Positive and Negative Feedback Homeostasis | Biology Dictionary (2024)

Homeostasis refers to the steady state of internal conditions maintained by living organisms. Humans have control centers in the brain and other parts of the body that constantly monitor conditions like temperature, pressure, and blood and tissue chemistry. When any condition gets out of balance, feedback loops return the body to homeostasis. This is a natural response to changes in the optimal conditions for the body to function.

To sense when things are out of balance, bodily functions have set points around which normal values fluctuate within a range. For example, normal human body temperature set point is 98.6°F, and the range varies a few degrees above and below that. There are positive and negative feedback loops in physiological processes that react when conditions venture outside the range.

Feedback loops have three components—the sensors, the control, and the effector. Sensors are also called receptors and they monitor conditions inside and outside the body. Some examples are thermoreceptors and mechanoreceptors. The control center, often in the brain, compares the value the sensor receives to the values in the range. Finally, the effector is what the feedback loop acts on.

Negative Feedback Loops

In the human body, this kind of feedback loop acts to resist or reverse the process when conditions go outside of the range.

Body Temperature

Core body temperature in mammals is regulated by thermoreceptors in the hypothalamus in the brain, spinal cord, large veins, and internal organs. When the core temperature gets too high, the animals first reaction is usually behavioral thermoregulation, also called allostasis. The animal may seek shade to get out of the sun or move into the water to cool its skin. This type of thermoregulation is the primary reaction because the effects will occur faster than the physiological mechanisms. It is important to realize that this feedback mechanism is based on controlling heat loss or heat gain in the body. The body does not “cool itself” in the literal sense, meaning it does not turn on an internal air conditioning system or synthesize chemicals that cool the body.

The major thermoregulatory negative feedback loop for cooling is when thermoreceptors on the skin detect higher than desired temperatures. This stimulates cholinergic sympathetic nerves to activate sweat glands in the skin to secrete sweat which evaporates and cools the skin and the blood in the vessels running through it. In animals like dogs and cats that have no sweat glands, the allostatic response is panting through the mouth to increase heat loss from the lungs. The stimulation of the sympathetic nerves decreases as the core temperature lowers back to the normal range.

If the core temperature becomes too cool, the first response is usually shivering (the allostatic response). Physiologically, the thermoreceptors trigger vasoconstriction in the skin and also reduces the flow of blood to the limbs. This moves more blood to the trunk of the body via the deep veins. In the trunk there is a counter-current exchange system where the veins run alongside the arteries, transferring some heat from the arterial blood to the venous blood.
Other examples of negative feedback loops include the regulation of blood sugar, blood pressure, blood gases, blood pH, fluid balance, and erythropoiesis.

Positive Feedback Loops

Instead of reversing it, positive feedback encourages and intensifies a change in the body’s physiological condition, actually driving it farther out of the normal range. This type of feedback is normal for the body, provided there is a definite endpoint.

Blood Clotting

The process of blood coagulation (hemostasis) is a cascading positive feedback loop. When the body is damaged inside or outside, the damaged tissues release factors that cause platelets to adhere to the tissue (the effector) at the site of the wound. The platelets release granules that activate and attract more platelets and cause them to bind to each other. Fibrinogen is converted to fibrin which creates a meshwork that traps blood cells and platelets, forming a clot and stopping the bleeding. The cascade comes to an end when thrombin binds to the cofactor thrombomodulin, activating protein C which inhibits the coagulation cycle.

Chemically, the activation of the enzyme prothrombin into its active form thrombin is one step in the clotting process. But what makes this a positive feedback loop is that thrombin can also activate the coagulation factors that precede it in the cascade. In other words, an increase in thrombin leads to a greater increase in thrombin. Figure 1 shows how thrombin regulates its own generation by activating clotting factors V, VIII, and XI.

Childbirth

Once labor begins, it is critical the process proceed quickly, or the life of the mother and baby will be at risk. The cascade of muscular events involved in labor and delivery are the result of a positive feedback system which is designed to do this.

The stimulus for the process to begin is the first contraction of labor. As the baby is pushed toward the cervix by the powerful contractions of the uterus, stretch sensors in the uterus monitor how much the cervix stretches. The sensors send messages to the pituitary gland in the brain, causing it to release the hormone oxytocin into the mother’s bloodstream. Oxytocin acts on the smooth muscle cells of the uterus (the effectors) causing stronger contractions, moving the baby farther down the birth canal. This continuous cycle of stretching and releasing of oxytocin stops only when the baby is expelled from the birth canal (the endpoint).

References

  • OpenStax College. (2018). Anatomy & Physiology. Houston, TX. OpenStax CNX. Retrieved from http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.119
  • Homeostasis. (n.d.). In Wikipedia. Retrieved March 30, 2018 from https://en.wikipedia.org/wiki/Homeostasis
Positive and Negative Feedback Homeostasis | Biology Dictionary (2024)

FAQs

Positive and Negative Feedback Homeostasis | Biology Dictionary? ›

Homeostasis typically involves negative feedback loops that counteract changes of various properties from their target values, known as set points. In contrast to negative feedback loops, positive feedback loops amplify their initiating stimuli, in other words, they move the system away from its starting state.

What is positive feedback and what is negative feedback? ›

Positive feedback occurs to increase the change or output: the result of a reaction is amplified to make it occur more quickly. Negative feedback occurs to reduce the change or output: the result of a reaction is reduced to bring the system back to a stable state.

What is an example of positive feedback in the body? ›

The release of oxytocin from the posterior pituitary gland during labor is an example of positive feedback mechanism. Oxytocin stimulates the muscle contractions that push the baby through the birth canal. The release of oxytocin result in stronger or augmented contractions during labor.

What is a simple definition of a negative feedback loop? ›

A negative feedback loop is a normal biological response in which the effects of a reaction slow or stop that reaction. A negative feedback loop helps regulate health by ensuring that a reaction is appropriate and that the systems of the body are in a constant state of equilibrium, also known as homeostasis .

What are examples of negative feedback? ›

18 Negative Feedback Examples: How to give negative feedback
  • Lack of punctuality.
  • Poor quality of work.
  • Poor communication.
  • Lack of collaboration.
  • Lack of initiative.
  • Failure to meet deadlines.
  • Not following processes.
  • Not paying attention to details.
May 7, 2023

What is the difference between positive and negative feedback in homeostasis? ›

Positive feedback systems in living things usually happen in response to a physiological stressor, such as blood clotting or childbirth. Negative feedback systems in living things continuously regulate critical body processes including temperature, pH, and hormone regulation to maintain homeostasis.

What is the difference between negative and positive feedback quizlet? ›

c.In a negative feedback system, the control center signals the effector to go "on and off" to maintain a steady state (or stable equilibrium); in a positive feedback system, the effector keeps increasing its output.

Is sweating positive or negative feedback? ›

If the temperature is high, the body sweats in order to cool down. Since the process of sweating is done to stop the temperature change, this is a negative feedback. Feedback loops come in two flavors: positive and negative. A negative feedback loop reduces the effect of change and helps maintain balance.

Is blood clotting a positive or negative feedback? ›

Blood clotting is another example of positive feedback.

Is shivering a positive or negative feedback? ›

Answer and Explanation: Shivering in response to a cold environment is an example of negative feedback because shivering is an adverse change in response to a cold environment. Shivering brings body temperature to an optimal state by contraction of muscles.

Is childbirth positive or negative feedback? ›

Figure 1.3. 3 – Positive Feedback Loop: Normal childbirth is driven by a positive feedback loop. A positive feedback loop results in a change in the body's status, rather than a return to homeostasis. The first contractions of labor (the stimulus) push the baby toward the cervix (the lowest part of the uterus).

Which best defines negative feedback? ›

Negative feedback can be defined as a system where outputs mute or moderate the initial inputs, with a dampening effect.

What is positive and negative feedback for students? ›

Positive feedback focuses on the strengths of the student and increases student motivation, whereas negative feedback focuses on the student's weaknesses and often decreases motivation.

What is a simple definition of a positive feedback loop? ›

For human-related systems, a positive feedback loop is defined as a system responding so that an idea or action has a positive effect on the original idea or action.

What is a positive feedback example? ›

Positive feedback you can give: "I'm really happy with your determination to finish this project. I know it wasn't easy, but I knew you could do it. Your helpful attitude makes it clear that you can continue to take on new challenges and grow with the company.

What are some examples of positive feedback in homeostasis? ›

What is an example of positive feedback in homeostasis? Let's take a look at some of the examples: clot formation, childbirth, fruit ripening, and menstrual cycle. Each one depicts what a positive feedback mechanism is like: Clotting factors are released to seal a wound.

What is the difference between negative and positive? ›

Positive numbers are those which are greater than zero. Negative numbers are those which are less than zero. Below is a table to help you remember what to do with the sign when using multiplication or division and addition or subtraction. For more information see positive and negative numbers in our Numeracy section.

What is positive vs negative feedback learning? ›

Positive feedback is used to indicate that an expected or desired behavior was demonstrated, or to reinforce successive steps toward a goal. Negative feedback indicates that a behavior or task was not performed correctly, thus indicating that a change of behavior is needed [4].

What is positive and negative feedback of hormones? ›

A feedback mechanism is a loop that a product feeds into in order to manage its own production. Positive and negative feedback mechanisms are two different types of feedback mechanisms. Positive feedback stimulates and increases hormone secretion. Negative feedback stops and inhibits the hormone from being produced.

What is positive and negative constructive feedback? ›

While positive feedback celebrates accomplishments, negative feedback addresses areas for refinement and growth opportunities. Though challenging, constructive negative feedback can potently catalyze personal and professional development.

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