Depressor reflex: how blood pressure is lowered
When blood pressure rises, the depressor reflex mechanism is engaged to return parameters to normal.
- The signal enters the nucleus tractus solitarius, from which it is transmitted via inhibitory interneurons to the vasomotor center.
- This leads to the inhibition of the vasomotor center and a decrease in descending sympathetic output.
- Sites of action:
- Heart (via \beta_1-adrenergic receptors) — overall cardiac workload decreases.
- Resistance vessels (via \alpha_1-adrenergic receptors) — vascular tone drops.
Pressor reflex: reaction to a drop in blood pressure
A sudden drop in blood pressure triggers the opposite process — the pressor reflex.
- This mechanism is activated during sudden changes in body position, such as during an orthostatic test when moving from a lying to a standing position.
- The system operates in reverse, engaging mechanisms for the urgent elevation and stabilization of the dropped blood pressure.
Baroreceptor resetting phenomenon
In chronic uncontrolled hypertension, the sensitivity of the receptor apparatus changes.
- The resetting phenomenon develops.
- Baroreceptor sensitivity drops quite rapidly — in just 1–2 days.
- As a result, the body begins to perceive elevated blood pressure levels as completely normal.
Clinical significance of adaptation during therapy
Changes in baroreceptor sensitivity directly affect the efficacy of hypertension treatment.
- If blood pressure is artificially lowered with medications to true normal levels, the body perceives this state as hypotension.
- In response, protective compensatory reactions are triggered:
- Reflex tachycardia occurs.
- Body water is retained.
- Conclusion: the overall efficacy of ongoing antihypertensive therapy is markedly reduced.
Depressor — down (heart and vessels via beta-1 and alpha-1 inhibit activity), Pressor — up (rescues during abrupt standing).
Class and exam questions
How does the depressor reflex work during elevated BP?
The nucleus tractus solitarius inhibits the vasomotor center via inhibitory interneurons. This reduces sympathetic influences on the heart via beta-1 adrenergic receptors and on resistance vessels via alpha-1 adrenergic receptors, decreasing cardiac work and vascular tone.
In what situations is the pressor reflex triggered?
The pressor reflex is activated during a sudden drop in blood pressure, for example, during an orthostatic test upon a rapid transition from a horizontal to a vertical position.
What is the baroreceptor "resetting" phenomenon?
This is the process of decreased baroreceptor sensitivity during uncontrolled blood pressure elevation, which develops within 1–2 days. In this process, the body begins to perceive elevated pressure as normal.
Why might treatment efficacy decrease during medical blood pressure lowering?
Due to baroreceptor resetting, the normalization of blood pressure is perceived by the body as hypotension. In response, compensatory mechanisms are triggered — reflex tachycardia and water retention, which raise the blood pressure.
What else to study on this topic
- The role of the nucleus tractus solitarius in autonomic regulation
- Involvement of the sympathetic nervous system in hemodynamic control
- Pharmacological effects of beta-1 and alpha-1 adrenergic receptor blockade
- Characteristics of orthostatic reactions in patients with hypertension
- Mechanisms of water retention during compensation of hypotensive states
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