Positive And Negative Feedback Loops - Negative Feedback Loops - Positive Feedback Loops

In this video we discuss homeostatic feedback control loops, including negative and positive control loops, and how they help keep the body in a state of homeostasis.



Positive and negative feedback in control systems - Control of homeostasis


There are many different feedback control loops in the body, and these homeostatic control systems can be based on positive or negative feedback.

Negative feedback control loops are the more common of the two, and they respond to a change by helping the body maintain a stable, homeostatic condition. An example of this is when body temperature starts to change. When it is cold out, and body temperature decreases below the set point range, the negative feedback loop will cause the body to shiver, producing heat, and ultimately body temperature will return to within the set point range.

The negative feedback loop will do the same if body temperature increases, like during exercise. The negative feedback loop will cause the body to sweat, which will reduce body temperature to within the set point range.

Positive feedback control loops do not help the body maintain a stable, homeostatic condition. Positive feedback control loops amplify the change that is happening to the body. So, let’s say that someone has a bacterial infection. The immune system signals the brain to increase the body’s temperature set point, causing the person to have a fever.

This can be a natural normal reaction, however, in some instances, it could create a harmful positive feedback loop, where metabolic rate is elevated and the body is producing heat faster than it can get rid of. So, a person may be shivering and sweating at the same time. And, if body temperature increases above 108 degrees, 42 c, it could be dangerous and even fatal.

In a couple of instances, positive feedback control loops can be beneficial to the body, such as when a blood vessel gets damaged. Lets say someone gets a cut in a blood vessel wall. A positive feedback control loop begins, and platelets, which are floating around in circulating blood, recognize the damaged area and begin to stick together to slow the loss of blood and patch up the tear in the wall.

They also release chemicals that attract more platelets to the area to help stop the blood loss. Eventually a blood clot is formed, the loss of blood is kept to a minimum, and the positive feedback loop ends.

Timestamps
0:00 Overview of feedback control loops
0:15 Negative feedback control loops
0:56 Positive feedback control loops