14.14: Glucocorticoids
- Page ID
- 84117
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Source and Control of Secretion
Glucocorticoids are a mixture of more than 12 steroid hormones secreted by selected cells in the adrenal cortex, the outer region of the adrenal glands (Figure 14.1). The main glucocorticoid is cortisol.
Glucocorticoid secretion is controlled by a negative feedback system that resembles the mechanism controlling thyroid hormone secretion. Activities in the hypothalamus and other brain areas cause a circadian rhythm in glucocorticoid secretion and blood levels. Peak secretion is at about the time of awakening in the morning, and slowest secretion occurs at approximately midnight.
Effects
Glucocorticoids have many types of target cells and produce a variety of responses, including increases in glucose production and release by the liver, leading to an increase in the blood glucose level; fat breakdown to supply energy for cells; breakdown of proteins to supply free amino acids; and vasoconstriction to increase blood pressure. Glucocorticoid secretion increases in times of stress because these four responses help the body overcome threats to homeostasis. Glucocorticoids also inhibit the inflammatory response and therefore reduce the accompanying pain, itching, and/or swelling. This effect has led to the widespread use of several forms of glucocorticoidlike medications (e.g., cortisone, hydrocortisone, prednisone) to treat many physical injuries, skin disorders, and chronic inflammatory diseases (e.g., arthritis).
Besides these responses, glucocorticoids cause five undesirable effects. These effects are suppression of cartilage and bone formation; stimulation of bone demineralization; promotion of GI tract bleeding and ulcer formation; damage to memory centers in the brain (i.e., hippocampus); and inhibition of portions of the immune response. The last effect increases susceptibility to infection when a person experiences severe stress.
When glucocorticoidlike steroids (corticosteroids) are administered therapeutically to reduce inflammation, their blood levels often rise above those established by internal negative feedback controls. This situation increases the number of unwanted effects. Older persons are especially susceptible to higher risks of glucose intolerance and diabetes mellitus, high blood pressure, osteoporosis, and infections. These risks can be reduced by using minimal doses, administering alternative forms of corticosteroids, or simultaneously instituting other medications or diet modifications to counteract the side effects. Alternatively, using nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce these risks. However, NSAIDs promote certain problems, including ulcer formation in the GI tract and kidney malfunction.
Age Changes
In healthy adults, aging causes no change in blood levels of glucocorticoids or the circadian rhythm of those levels. Therefore, aging seems to have no adverse effect on the contribution of glucocorticoids to homeostasis. However, there is a small age-related decrease in the sensitivity of the negative feedback mechanisms that control glucocorticoid levels. This change may lead to abnormally high levels in elderly individuals with disorders (e.g., Alzheimer's disease, depression) that reduce the effectiveness of the glucocorticoid control mechanism even further.