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37.11: Regulation of Body Processes - Hormonal Regulation of Stress

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    Learning Objectives
    • Describe the role of the adrenal glands in the “fight-or-flight” response and the body’s reaction to stress

    When a threat or danger is perceived, the body responds by releasing hormones that will ready it for the “fight-or-flight” response. The effects of this response are familiar to anyone who has been in a stressful situation: increased heart rate, dry mouth, and hair standing erect.

    The sympathetic nervous system regulates the stress response via the hypothalamus. Stressful stimuli cause the hypothalamus to signal the adrenal medulla (which mediates short-term stress responses) via nerve impulses, and the adrenal cortex, which mediates long-term stress responses via the hormone adrenocorticotropic hormone (ACTH), which is produced by the anterior pituitary.

    Short-term Stress Response

    Interactions of the endocrine hormones have evolved to ensure the body’s internal environment remains stable. Stressors are stimuli that disrupt homeostasis. The sympathetic division of the vertebrate autonomic nervous system has evolved the fight-or-flight response to counter stress-induced disruptions of homeostasis. In the initial alarm phase, the sympathetic nervous system stimulates an increase in energy levels through increased blood glucose levels. This prepares the body for physical activity that may be required to respond to stress: to either fight for survival or to flee from danger.

    image
    Figure \(\PageIndex{1}\): Fight-or-flight response: When an animal feels threatened, epinephrine and norepinephrine released by the adrenal medulla prepare the body to fight a threat or flee from it by breaking down stores of glycogen, which provides an immediate boost of energy.

    When presented with a stressful situation, the body responds by calling for the release of hormones that provide a burst of energy. The hormones epinephrine (also known as adrenaline) and norepinephrine (also known as noradrenaline) are released by the adrenal medulla. Epinephrine and norepinephrine increase blood glucose levels by stimulating the liver and skeletal muscles to break down glycogen and by stimulating glucose release by liver cells. Additionally, these hormones increase oxygen availability to cells by increasing the heart rate and dilating the bronchioles. The hormones also prioritize body function by increasing blood supply to essential organs, such as the heart, brain, and skeletal muscles, while restricting blood flow to organs not in immediate need, such as the skin, digestive system, and kidneys. Epinephrine and norepinephrine are collectively called catecholamines.

    Long-term Stress Response

    Some stresses, such as illness or injury, can last for a long time. Glycogen reserves, which provide energy in the short-term response to stress, are exhausted after several hours and cannot meet long-term energy needs. If glycogen reserves were the only energy source available, neural functioning could not be maintained once the reserves became depleted due to the nervous system’s high requirement for glucose. In this situation, the body has evolved a response to counter long-term stress through the actions of the glucocorticoids, which ensure that long-term energy requirements can be met. The glucocorticoids mobilize lipid and protein reserves, stimulate gluconeogenesis, conserve glucose for use by neural tissue, and stimulate the conservation of salts and water.

    Long-term stress response differs from short-term stress response. The body cannot sustain the bursts of energy mediated by epinephrine and norepinephrine for long times. Instead, other hormones come into play. In a long-term stress response, the hypothalamus triggers the release of ACTH from the anterior pituitary gland. The adrenal cortex is stimulated by ACTH to release steroid hormones called corticosteroids. Corticosteroids turn on transcription of certain genes in the nuclei of target cells. They change enzyme concentrations in the cytoplasm and affect cellular metabolism.

    There are two main corticosteroids: glucocorticoids, such as cortisol, and mineralocorticoids, such as aldosterone. These hormones target the breakdown of fat into fatty acids in the adipose tissue. The fatty acids are released into the bloodstream for other tissues to use for ATP production. The glucocorticoids primarily affect glucose metabolism by stimulating glucose synthesis. Glucocorticoids also have anti-inflammatory properties through inhibition of the immune system. For example, cortisone is used as an anti-inflammatory medication; however, it cannot be used long term as it increases susceptibility to disease due to its immune-suppressing effects. Mineralocorticoids function to regulate ion and water balance of the body. The hormone aldosterone stimulates the reabsorption of water and sodium ions in the kidney, which results in increased blood pressure and volume.

    Hypersecretion of glucocorticoids can cause a condition known as Cushing’s disease, characterized by a shifting of fat storage areas of the body. This can cause the accumulation of adipose tissue in the face and neck, and excessive glucose in the blood. Hyposecretion of the corticosteroids can cause Addison’s disease, which may result in bronzing of the skin, hypoglycemia, and low electrolyte levels in the blood.

    Key Points

    • When the body senses stress, the hypothalamus signals the adrenal medulla to release epinephrine or norepinephrine, or the anterior pituitary to release ACTH.
    • In short-term stressful situations, such as when a threat is perceived, epinephrine (adrenaline) and norepinephrine (noradrenaline) are released to prepare the body for a “fight-or-flight” response.
    • Epinephrine and norepinephrine act to provide a burst of energy to the body by stimulating the breakdown of glycogen into glucose, increasing the heart rate, and dilating the bronchioles.
    • In long-term stress situations, such as when the body must deal with injury or illness, ACTH is released, stimulating the production of corticosteroids, which include glucocorticoids and mineralocorticoids.
    • Glucocorticoids stimulate the synthesis of glucose and inhibit the immune system.
    • Mineralocorticoids regulate ion and water balance of the body by stimulating the kidneys to excrete less water and sodium ions in the urine.

    Key Terms

    • epinephrine: (adrenaline) an amino acid-derived hormone secreted by the adrenal gland in response to stress
    • norepinephrine: a neurotransmitter found in the locus coeruleus which is synthesized from dopamine
    • corticosteroid: any of a group of steroid hormones, secreted by the adrenal cortex, that are involved in a large range of physiological systems
    • mineralocorticoid: any of a group of steroid hormones, characterised by their similarity to aldosterone and their influence on salt and water metabolism
    • catecholamine: any of a class of aromatic amines derived from pyrocatechol that are hormones produced by the adrenal gland
    • glucocorticoid: any of a group of steroid hormones, produced by the adrenal cortex, that are involved in metabolism and have anti-inflammatory properties
    • adrenocorticotropic hormone: a peptide hormone, secreted by the pituitary gland, that stimulates the secretion of other hormones

    Contributions and Attributions

    This page titled 37.11: Regulation of Body Processes - Hormonal Regulation of Stress is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Boundless.

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