Question 1

What is the Meaning of Salivary Cortisol Diurnal Rhythm?

Accepted Answer

The Salivary Cortisol Diurnal Rhythm is the characteristic, predictable pattern of cortisol concentration changes in saliva measured across a complete 24-hour period. Cortisol levels typically exhibit a sharp rise shortly after waking (the Cortisol Awakening Response), decline gradually throughout the day, and reach their lowest point around midnight. Measuring this rhythm via multiple salivary samples provides a non-invasive, accurate assessment of the HPA axis function and its synchronization with the body's circadian clock. Deviations from this expected rhythm, such as a flattened or inverted curve, are critical clinical indicators of chronic stress or HPA axis dysregulation requiring intervention.

Question 2

What is the Origin of Salivary Cortisol Diurnal Rhythm?

Accepted Answer

This term originates from chronobiology and clinical endocrinology, leveraging the fact that cortisol measured in saliva represents the free, biologically active fraction of the hormone, unbound to carrier proteins. The rhythmic pattern itself is an evolutionary adaptation, synchronizing energy mobilization with the anticipated demands of the waking day. Salivary testing became a preferred method due to its non-invasive nature and its accurate reflection of the unbound, active hormone fraction at the tissue level.

Question 3

What is the Mechanism of Salivary Cortisol Diurnal Rhythm?

Accepted Answer

The rhythm is fundamentally governed by the master clock in the suprachiasmatic nucleus (SCN) of the hypothalamus, which sends timed signals that regulate the pulsatile release of CRH and ACTH. ACTH then stimulates the adrenal glands to synthesize and release cortisol in a rhythmic, circadian-driven manner. The characteristic morning rise is a proactive physiological preparation for the anticipated daily stress and energy demands, while the steep evening decline facilitates the necessary onset of sleep and metabolic rest.

Salivary Cortisol Diurnal Rhythm

Meaning

Origin

Mechanism

Are There Quantifiable Biomarkers to Assess the Success of Lifestyle Modifications on HPA Axis Load?

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