Homeostasis : definition, and mechanism | B.pharma 2nd sem. Notes 

Homeostasis may be defined as “The maintenance of the internal conditions of the body at equilibrium, despite changes in the external environment”. For example, the core temperature of the human body remains at about 37°C despite fluctuations in the surrounding temperature. 

Negative Feedback Loops:

Nearly, all physiologic adaptive responses are negative feedback loops. These processes act to restore homeostasis by inducing changes in the opposite direction of a force perturbing the system. Homeostasis is a temperature control that is vital to the maintenance of homeostasis within the body. Heat is sensed by thermo- regulators in both, the skin and the hypothalamus. The internal temperature is sensed by the hypothalamus, and the external temperature is sensed by the skin. When the external temperature outside is too cold, messages are sent from the many thermo- receptors located within the skin to the cerebellum leading to the hypothalamus. The role of the cerebellum is to make the individual aware of feeling cold, which may cause voluntary behavioral changes such as putting on more layers of clothing or a coat. Homeostatic processes are controlled by negative feedback and hence these systems occur more commonly within the body. 

Positive Feedback Loops: 

Positive feedback loops are almost always maladaptive or harmful and are often termed vicious cycles, downward spirals, or decompensation states. Two positive feedback mechanisms control the release of oxytocin: 

• Uterine contractions during childbirth: When contractions start, oxytocin is released which stimulates more contractions and more oxytocin is released, hence contractions increase in intensity and frequency. Production and release of oxytocin stop after the baby is delivered. 

•Secretion of breast milk: The stimulation of a baby sucking its mother’s breast leads to the secretion of oxytocin into the mother’s blood, which leads to milk being available to the baby via the breast. The mother’s production and release of oxytocin cease when the baby stops feeding.