Cortisol Circadian Rhythm — HPA Axis (2D)

Time of day

Clock time 07:00

Wake-up time 07:00

Acute stress event

Stress onset 14:00

Stress intensity 1.0×

HPA axis feedback

Negative feedback gain 1.0×

Live signal

CRH (hypothalamus)

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ACTH (pituitary)

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Plasma cortisol

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How it works

The hypothalamus, pituitary and adrenal cortex form a closed loop: hypothalamic CRH drives pituitary ACTH, which drives adrenal cortisol — and rising cortisol feeds back to suppress CRH and ACTH. This simulator integrates that loop minute-by-minute across the 24-hour clock:

Pre-dawn drive — an excitatory signal to the hypothalamus builds in the hours before your chosen wake time, exactly as CRH-neuron excitability does in life.
Cortisol awakening response (CAR) — because CRH → ACTH → cortisol each lag the signal before them, cortisol keeps climbing for 30–45 minutes after waking even as the drive itself is already falling — the real documented CAR overshoot.
Negative feedback — cortisol suppresses further CRH/ACTH output in proportion to the feedback-gain slider; turn it to zero and the rhythm loses its self-limiting shape and stays elevated all day.
Stress spike — an acute stress event injects an extra pulse into CRH at the chosen clock time, superimposed on top of the ordinary circadian curve, and you can watch feedback pull it back down afterward.

The scrolling curve shows a full 24h cycle computed from three simulated cycles of the loop, so the shown day is already in its stable, repeating rhythm — not a cold-start transient.

CRH ACTH Cortisol