Introduction, Definitions, Homeostasis, Components and Types of Feedback systems

Introduction and definition

By maintaining constant internal conditions, living organisms maintain internal chemical, physical, and biological homeostasis. Homeostasis refers to the inside of the body being constant. The condition of dynamic equilibrium is when many variables, such as body temperature and balance of fluids are kept within an adequately defined range (homeostatic range), in order for the organism to function at its best. Besides pH, salt, potassium, calcium and sodium ions concentrations, blood sugar levels are other variables that need to be regulated regardless of environmental changes, diet, or physical activity levels.

A homeostatic mechanism, which maintains balance between each of these variables, controls each of them.

Components of homeostasis

As a result of the self-regulating devices in the body, the homeostatic system operates in a cyclical fashion. Four components make up this cycle:

• A sensor or detector that detects deviations
• A control center is receiving this message.
• Messages and information are transmitted from the control center to the effectors for correction of the deviation. This may be a physical process involving nerve impulses or a chemical process involving hormones or blood flow.
• A correction factor that corrects deviations.

Types of feedback systems

Multiple body systems are maintained in a normal state by the homeostatic mechanism. Whenever the behavior patterns of any system change, the effectors either inhibit and reverse the change or support and accelerate the change, depending on the situation that arises. These are accomplished through feedback signals.

The term feedback refers to the condition of passing some part of the output signal back to the input. The system is often controlled in this way intentionally to control behaviour patterns. Two types of feedback are received and acted upon whenever a change occurs to the system:

• Negative feedback
• Positive feedback

Negative feedback

When the system experiences negative feedback, it reacts in a way that stops or reverses the direction of change. Signals are sent back from effectors to the system following the receipt of a message. Now, the system attempts to maintain homeostasis by stabilizing itself.





Negative feedback is essential to many homeostatic mechanisms within the body. Thyroxine is secreted by the thyroid gland when thyroid-stimulating hormone (TSH) is released from the pituitary gland. Increasing levels of thyroxine in the blood inhibit the pituitary's secretion of thyroid stimulating hormone, so that the thyroid gland's production of thyroxin decreases. The pituitary gland releases TSH when thyroxine secretion is low due to low blood levels of thyroxine. Now, TSH stimulates thyroxine production by the thyroid gland. Maintaining water balance in the body is another example of a negative feedback mechanism.

Positive feedback

Positive feedback occurs when the system reacts to a change in the same direction by increasing the intensity of that change. Generally, negative feedback is more widespread. Nevertheless, in emergency situations, positive feedback can have considerable significance. When blood clots, it has a positive feedback effect. When an injury occurs, blood clotting occurs in three stages. During the first stage:

• Prothrombin activating factor formation
• Prothrombin is converted into thrombin
• Fibrinogen is transformed into fibrin.

Thrombin formed in the second stage induces prothrombin activator production along with the conversion of fibrinogen into fibrin. It stimulates the production of increasing amounts of prothrombin activator, which speeds up the clotting process and prevents blood loss quickly. Milk ejects ions reflex and parturition are other processes where positive feedback occurs, and both processes involve oxytocin secretion.



Positive feedback during parturition




Positive and negative feedback




Positive feedback

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