Physical stresses include exposing the body to injury, walking outside in cold and wet conditions without a coat on, or malnutrition. Stress can be either physical or psychological or both. One of the major functions of the adrenal gland is to respond to stress. The medulla is stimulated to secrete the amine hormones epinephrine and norepinephrine. The sympathomedullary (or SAM: Sympathetic-Adrenal-Medulla) pathway involves the stimulation of the medulla by impulses from the hypothalamus via neurons from the thoracic spinal cord. It is really an extension of the autonomic nervous system, which regulates homeostasis in the body. The adrenal medulla is neuroendocrine tissue composed of postganglionic sympathetic nervous system (SNS) neurons. ACTH then stimulates the adrenal cortex to produce the hormone cortisol. The HPA axis involves the stimulation of hormone release of adrenocorticotropic hormone (ACTH) from the pituitary by the hypothalamus. The adrenal cortex, as a component of the hypothalamic-pituitary-adrenal (HPA) axis, secretes steroid hormones important for the regulation of the long-term stress response, blood pressure and blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation. The adrenal gland consists of an outer cortex of glandular tissue and an inner medulla of nervous tissue. (Image credit: "The Adrenal Glands" by Julie Jenks is licensed under CC BY 4.0 / A derivative from the original work / Micrograph provided by the Regents of University of Michigan Medical School © 2012) The adrenal medulla releases stress hormones such as epinephrine and norepinephrine that stimulate the sympathetic autonomic nervous system (ANS). The cortex can be subdivided into additional zones listed from superficial to deep: the zona glomerulosa that releases mineralocorticoids such as aldosterone to regulate mineral balance, the zona fasciculata that releases glucocorticoids such as cortisol, corticosterone, and cortisone to regulate glucose metabolism, and the zona reticularis that releases androgens such as dehydroepiandrosterone that stimulate masculinization.
Both adrenal glands sit atop the kidneys and are composed of an outer cortex and an inner medulla, all surrounded by a connective tissue capsule.
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