The endocrine system performs key tasks in regulating homeostasis. The release of endocrine hormones, or chemical messengers are essential in maintaining normal physiological function. Hormones are first released by the most important endocrine gland, the brain. Nerve cells in the hypothalamus synthesize releasing factor hormones and secrete them to the pituitary via the axon of the nerve terminals. After reaching the pituitary, trophic hormones are secreted to other endocrine organs via the blood to perform specific tasks in synthesizing hormones which perform processes in maintaining health. Negative feedback loops allow the synthesized hormones of the glands to act on the hypothalamus and pituitary for regulation to maintain homeostasis. These processes are important because if not maintained properly, can lead to disease.
The adrenals play an important role in the endocrine system. Under normal conditions, the hypothalamus releases corticotrophin releasing hormone (CRH) which acts on the pituitary. The pituitary then releases corticotrophin, or adrenocorticotrophic-stimulating hormone (ACTH). ACTH stimulates adrenal steroid synthesis in the adrenal glands. The cortex of the adrenals secretes glucocorticoids from the zona fasciculata, mineralocorticoids from the zona glomerulosa, and sex hormones from the zona reticularis. It is important that glucocorticoids and mineralocorticoids such as cortisol and aldosterone, respectively, are released. Cortisol regulates blood glucose levels and aids in the metabolism of lipids, proteins, and carbohydrates. Aldosterone regulates blood pressure and blood salt and potassium levels. To create homeostasis, once a certain amount of hormone is released it can act on the pituitary and the hypothalamus to stop the production of releasing hormones and/or trophic hormones.
Although rare, this process can result in an adrenal insufficiency. The most common adrenal insufficiency is secondary adrenal insufficiency. Secondary adrenal insufficiency or ACTH deficiency is due to a decrease or absence of adrenocorticotrophic-stimulating hormone (ACTH) due to suppression of the pituitary. With little or no release of ACTH, the cortex of the adrenal glands is unable to respond to release cortisol. Aldosterone is unaffected because it is not completely dependent on ACTH; its major regulators are angiotensin II and potassium.
The low production of ACTH could be due to a pituitary tumor; however, it is most commonly affected by the prolonged use of glucocorticoid medications. Glucocorticoids, such as fluticasone propionate, are commonly used in the treatment of asthma. The body recognizes glucocorticoids as cortisol; they, in turn, stimulate the pituitary as negative feedback. They signal the pituitary to reduce the release of ACTH. In return, the body synthesizes less cortisol for its biological processes.
Laura Baker was prescribed high dosages of fluticasone propionate at the age of two to control her severe asthma symptoms. 17 years later, after experiencing symptoms of fatigue, loss of appetite, weight loss, nausea, vomiting, diarrhea, and muscle weakness she visited her doctor and had lab test performed. Her tests showed normal potassium and sodium blood levels; however, there was no presence of cortisol or ACTH. After reviewing her medical history, she was diagnosed with ACTH deficiency or secondary adrenal insufficiency at the age of twenty. The prolonged use of the high dosage of fluticasone propionate suppressed the pituitary. The suppression of the pituitary decreased the secretion of ACTH, suppressing cortisol secretion, and causing her unfavorable symptoms.
To treat ACTH deficiency, hormone replacement therapy is utilized. Oral hydrocortisone is given at a dosage similar to cortisol that the body naturally produces. Hydrocortisone is cortisol when supplied as a medication. In Laura’s case, because the pituitary no longer secretes ACTH she must use the medication for the rest of her life to produce enough cortisol to maintain homeostasis.
To conclude, the endocrine system plays an important role in maintaining homeostasis in the body. The brain is a critical endocrine organ due to the hypothalamus and the pituitary. The hypothalamus releases hormones that stimulate trophic hormones in the pituitary to send signals to other endocrine organs to synthesize hormones to maintain homeostasis of biological processes. The adrenal glands are key endocrine gland which is the major control for the secretion of cortisol which regulates blood sugar and metabolism. The hypothalamus secretes CRH, to stimulate the anterior pituitary to secrete ACTH, which stimulates the adrenal cortex to secrete cortisol. In rare cases, the pituitary function can be suppressed and ACTH will not be secreted to signal the adrenals to release cortisol, resulting in low blood sugar and low levels of metabolic processes, called ACTH deficiency or secondary adrenal insufficiency. This can be corrected by taking oral hydrocortisone to produce normal levels of cortisol.