What is feedback control? Illustrate the feedback mechanism of homeostasis by an example of hormones.

Hint: Metabolic processes in the body have to be efficiently regulated depending on whether by products, intermediates, or end products increase or decrease in quantity. For this there has to be a means of interconnecting the stages.

Complete Answer:
- In biological systems, feedback mechanisms are when an end product or an intermediate either causes a process to increase or decrease. These are stimulatory or inhibitory feedback loops. In this way, metabolism can be regulated according to the need of a particular time, rather than wasting energy.
- A good example of such homeostasis is in hormonal feedback loops. These tend to be negative feedback: that is, the concentrations of the end product or hormone reduce the activity or production. An example of such a feedback loop in action involves thyroid function.
- When levels of T3 fall, the hypothalamus releases more TRH or thyrotropin releasing hormone. This stimulates the pituitary to produce and release more of TSH or thyroid stimulating hormone.
- As a result, the thyroid gland synthesizes and releases more of the thyroid hormones, T4 and T3. Once the levels of these hormones reach a particular concentration in the bloodstream, they in turn act on the hypothalamus and Pituitary to stop the production of TSH and TRH. In this way the thyroid gland does not produce too much of thyroid hormone or too little. Production can be controlled within fairly small ranges as well.

Note: Some hormones may be under positive feedback regulation. For instance, during childbirth oxytocin is released to stimulate contractions. At the same time, the pressure of the baby’s head on the cervix sends a signal back to the brain, leading to more oxytocin release.