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14.2: Main Functions for Homeostasis

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    Like the nervous system, the overall job of the endocrine system is to regulate parts of the body and ensure that they contribute to maintaining homeostasis. The main functions for homeostasis of this system are similar to four of those performed by the nervous system: monitoring, communicating, stimulating, and coordinating (Chapter 6). However, the endocrine system performs these functions somewhat differently.

    When an endocrine structure detects that a body condition is changing or has strayed from homeostasis, it secretes a hormone, which communicates information about the errant condition to other body cells. The hormone also causes alterations in cell activities to stop the change from occurring and bring the straying condition back into the homeostatic range. Often the hormone alters functions in many types of cells in several ways and therefore coordinates adaptive responses in various organs. For example, if the concentration of calcium in the blood declines, the parathyroid gland detects this change and secretes parathormone. The parathormone causes the blood calcium level to rise back to normal through its effects on bones, the small intestine, and the kidneys. The parathyroid gland then detects the rise in blood calcium and diminishes parathormone secretion, preventing the calcium concentration from rising too high. If calcium levels rise above a satisfactory level, the thyroid gland secretes thyrocalcitonin, which lowers blood calcium through its effects on bone matrix. Therefore, like the nervous system, the endocrine system performs the first two steps in negative feedback systems and contributes to the third by causing adaptive responses by parts of the body. Negative feedback responses are not governed simply by turning hormone secretions and the functions being controlled on and off as thermostats do in systems operating heaters and air conditions. Negative feedback control by the endocrine system can produce a continuous gradation and modulation in the rates of hormone secretion and functional alterations.

    Therefore, negative feedback responses in the endocrine system operate more like a driver who maintains a proper and fairly steady speed on a hilly highway by adjusting foot pressure on the accelerator and brake pedals of a vehicle. Furthermore, like slightly excessive foot pressure on an accelerator or a brake pedal, the amount of circulating hormone can become slightly too high or low. Though a small error may cause no harm over a short period, sustaining such a condition can result in substantial deviations in the condition being regulated. Normally, negative feedback responses prevent such occurrences. Finally, like an alert driver, the endocrine system is a highly sensitive and rapidly responsive negative feedback system that can reverse shifts in hormone levels quickly so that minimal fluctuations occur. There are a few situations in which the endocrine system provides positive feedback responses, which increase rather than decrease change. These situations involve functions in the female reproductive system that cause ovulation by the ovary and milk production by the breasts. These functions end during menopause.

    This page titled 14.2: Main Functions for Homeostasis is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Augustine G. DiGiovanna via source content that was edited to the style and standards of the LibreTexts platform.