Understanding Negative and Positive Feedback in Homeostasis Made Easy

Understanding Negative and Positive Feedback in Homeostasis
This Bodytomy article explains the biological phenomenon of homeostasis with examples of positive and negative feedback mechanisms. Here's how the failure of the system that helps maintain an internal equilibrium can lead to diseases and health issues.
Did You Know?
Biological homeostasis involves continuous checking, correcting, and maintaining the stability of systems within the body. The same principle is applicable to various processes from various fields. The law of supply and demand illustrates how homeostasis is applicable even to social sciences. According to this law, continuous interaction between supply and demand helps keep market prices fairly stable.
Homeostasis is a fundamental property of all living organisms, including plants and microorganisms. It helps them to survive in an ever-changing environment. This property enables the system to regulate certain variables like temperature, blood pressure, pH level, blood sugar, mineral levels, etc., so that body functions remain relatively stable despite ceaseless threats.

A simple example of a thermostat will help you understand this mechanism. The thermostat in an air conditioner senses the rise in temperature (a change in the given ideal value), and triggers the machine to switch on. Once the house is cooled, and the ideal value that is fed to the thermostat is achieved, the machine shuts down or switches off.
Important Components in Homeostatic Control Mechanisms
◆ Receptor
It monitors the environment and senses a stimulus (detects the change in the ideal value). It sends information to the next component involved―the control center.
◆ Control Center
It plays an important role in determining the ideal range for the value of the variable. According to the set value, this center takes appropriate decisions and sends commands (signals) to the third component called effector.
◆ Effector
In the human body, muscles, organs, glands, etc., act as effectors. After receiving a signal from the control center, the effectors try to bring back the value of the variable to the normal level, usually through negative feedback.
Negative Feedback
Usually, homeostasis, (in simple words, metabolic equilibrium) is maintained with the help of a number of chemical reactions. After sensing a change in a certain variable, the mechanism is usually activated to reduce or negate the value, and hence, it is called negative feedback.
Examples of Negative Feedback
✦ Temperature Control
Sweating man
As you know, 36.5 degrees Celsius is considered as normal body temperature. Hypothalamus, an important part of the brain, monitors body temperature. It is capable of detecting minute changes in the body. If the temperature drops, various muscles start shivering as they receive signals from the hypothalamus. Blood vessels under the skin constrict and try to hold warm blood. This helps increase the temperature. In case, the temperature rises, dilation of blood vessels under the skin helps direct more blood towards the surface of the skin. This eventually helps get rid of excess heat. Moreover, glands located under the skin are stimulated to produce more sweat. Excessive sweating helps reduce the heat. Thus the actions negate the effect of changed temperature.
✦ Blood Pressure Regulation
When blood pressure increases, blood vessels feel (as a receptor) the resistance of blood flow against their walls. So, they send signals to the brain. The brain in turn sends signals to the heart and blood vessels (both are effectors). As a result, blood vessels dilate (the process is called vasodilation). So, the heart rate decreases and blood pressure drops to its normal range. Thus, activation of corrective negative feedback loops plays an important role in bringing back the blood pressure to normal.
✦ Rate of Metabolism
When you deprive your body of food, the rate of metabolism slows down. To survive with reduced energy supply, cells function at a slower rate. Exercise helps speed-up the rate of metabolism.
✦ Blood Sugar Concentration
When you eat, blood sugar level rises. Pancreas (control center) releases the hormone insulin. It stimulates the cells to use up this excess glucose. If blood sugar level falls below the normal level, pancreas releases the hormone glucagon, which stimulates the liver to release stored glucose (glycogen) into the bloodstream.
✦ Some Other Simple Examples
Woman drinking water
A change in the internal environment causes a dry mouth, makes you feel thirsty, and indicates that you should drink water. A low concentration of oxygen leaves you breathless. Other examples include regulation of blood calcium levels, which involves release of parathyroid hormone from parathyroid glands, maintaining the pH within the range of 7.35 to 7.45, maintaining water balance, oxygen content of cells, etc. There exist innumerable examples.
Positive Feedback
While negative feedback tries to counterbalance the change in the value of a variable by negating the effect of the stimulus, positive feedback increases the original stimulus and intensifies its effect. As mentioned above, homeostasis involves the processes that help maintain optimum conditions for cells, in spite of the constantly changing environment (both internal and external). Since positive feedback increases the variable in the same direction, it does not help stabilize the system. Thus, it does not bring about homeostasis.
Examples of Positive Feedback
✦ Childbirth
Newborn baby with mother
Release of the hormone oxytocin induces labor. As the number and intensity of contractions increases, more and more oxytocin is released. This phenomenon ends when the child is born.
✦ Blood Clotting
Knee wound
If a blood vessel is ruptured, platelets gather at the injury site. They release certain enzymes which ensure that more and more thrombin is produced. Platelets accumulate at the site and as they cling together, a clot is formed. The process continues until bleeding stops completely. This promotes fast recovery of the wound and less loss of blood.
✦ Lactation
Mother breastfeeding
A crying or suckling baby initiates a nerve response that accelerates the production of prolactin by the pituitary gland. This helps produce more milk.
✦ Other examples include a sharp rise in estrogen during the follicular phase of the menstrual cycle resulting in ovulation, the act of producing nerve signals which involves a little leakage of sodium ions through sodium channels in the initial stage and an explosion of sodium leakage at the end.
Compare and Contrast
Negative Feedback Positive Feedback
The final effects are negative (opposite) to the stimulus. The original stimulus is encouraged rather than negated.
Finally, it ensures stability of the system. It is often a reason for speedy loss of internal stability.
This type of feedback is used frequently. It is used less frequently in our body.
It involves continuous modification. It does not require continuous adjustment.
It is usually directed to maintain hormone levels within normal range. It reduces the change (increase or decrease) in the normal value. Instead of inhibiting the original stimulus, it usually increases the deviation from the normal value and promotes abnormal levels.
It usually helps maintain homeostatic functions. It is rarely used to maintain homeostatic functions.
When the negative feedback loop that helps stabilize blood glucose levels fails, the person is said to have a disease called diabetes. Many diseases, like heart diseases, involve life-threatening positive feedback loops. For example, when a small part of the heart tissue dies, inadequate amount of blood is pumped by the heart. Heart itself becomes a victim of poor blood supply, which results in the death of some more part of its tissue. This eventually results in a heart attack and the death of the person. With aging, the efficiency of control systems reduces and risk for diseases increases, as the stability of the internal environment is slowly lost.
The nervous system and various hormones produced by the endocrine glands play an important role in regulating the negative and positive feedback loops. Healthy diet, regular exercise, and stress-free lifestyle help maintain hormonal balance.