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# Hypertension: mechanisms

- Mechanism

Blood pressure is cardiac output times resistance. Hypertension appears when the kidneys keep too much salt or the small arteries stay too narrow.

Updated Nov 12, 2026

## Key points

- BP = cardiac output × peripheral resistance; the kidney is the long-term regulator (pressure natriuresis).
- Essential hypertension is multifactorial: polygenic variants plus salt, obesity, inactivity, alcohol and stress.
- Renal causes are the commonest secondary causes: renal artery stenosis and chronic kidney disease.
- Endocrine causes: primary aldosteronism (common and underdiagnosed), pheochromocytoma, Cushing syndrome, thyroid disease.
- Rare single-gene forms change renal sodium handling (for example Liddle syndrome, glucocorticoid-remediable aldosteronism).
- Malignant hypertension: very high pressure with acute organ damage; arterioles show fibrinoid necrosis and hyperplastic change.

## What it is

Blood pressure is the product of cardiac output and peripheral vascular resistance, and in the long run the kidney sets it by controlling sodium balance through the renin–angiotensin–aldosterone system and natriuretic peptides. In about nine of ten people the cause is not found (essential, or primary, hypertension): many genetic variants, salt intake, obesity, stress and ageing add up. The rest have secondary hypertension from kidney, adrenal, vascular or other disease, which is worth finding because it may be curable.

## Step by step

- Arterial pressure falls or sodium delivery drops; the juxtaglomerular cells release renin.
- Renin makes angiotensin I; angiotensin-converting enzyme makes angiotensin II.
- Angiotensin II constricts arterioles and drives aldosterone release; aldosterone retains sodium and water.
- Higher volume and resistance raise pressure; normally the kidney then excretes more salt and pressure settles.
- In hypertension this set point is shifted: the kidney needs a higher pressure to excrete the daily salt load.
- Sustained pressure remodels arterioles and the heart, which locks the hypertension in.

## Secondary hypertension: the causes to recognise

| Cause | Mechanism | Clue |
| --- | --- | --- |
| [Renal artery stenosis (atheroma or fibromuscular dysplasia)](https://durgical.com/en/conditions/renovascular-hypertension/) | Low renal perfusion activates renin–angiotensin | Abdominal bruit, rising creatinine with ACE inhibitors |
| [Primary aldosteronism](https://durgical.com/en/conditions/primary-hyperaldosteronism/) | Autonomous aldosterone: sodium retention, potassium loss | Hypokalemia, high aldosterone with low renin |
| [Pheochromocytoma](https://durgical.com/en/conditions/phaeochromocytoma/) | Catecholamine excess | Paroxysms of headache, sweating, palpitations |
| [Cushing syndrome](https://durgical.com/en/conditions/cushing-syndrome/) | Glucocorticoid excess with mineralocorticoid effect | Central obesity, striae, hyperglycemia |
| [Coarctation of the aorta](https://durgical.com/en/conditions/coarctation-of-the-aorta/) | Fixed obstruction; low renal flow distal to it | Arm pressure higher than leg pressure, rib notching |
| [Obstructive sleep apnea](https://durgical.com/en/conditions/obstructive-sleep-apnoea/) | Repeated hypoxia and sympathetic surges | Snoring, daytime sleepiness, obesity |

## Clinical notes

- Hypertension is a major risk factor for coronary disease, stroke, heart failure, aortic dissection, kidney disease and dementia.
- Preeclampsia is a pregnancy-specific hypertensive disorder driven by abnormal placental vessels.

## Memory aid

Pressure is pump times pipes, and the kidney holds the thermostat: reset the thermostat and the whole house runs hot.

## Test yourself

Think of the answer, then tap the question to see it.

## Which organ sets blood pressure in the long term, and by what means?

The kidney, by adjusting sodium and water excretion (pressure natriuresis) under the renin–angiotensin–aldosterone system.

## Which laboratory pattern suggests primary aldosteronism?

Hypokalemia with a high aldosterone and a suppressed renin.

## What proportion of hypertension is essential (primary)?

About 90 % or more; a cause is identified in a minority.

## What arteriolar lesions define malignant hypertension?

Fibrinoid necrosis and hyperplastic (onion-skin) arteriolosclerosis, with acute damage to kidney, brain, eye and heart.

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## Elsewhere in DurgiPedia

- [Physiology of hypertension](https://durgical.com/en/physiology/physiology-of-hypertension/)
- [The renin–angiotensin–aldosterone system](https://durgical.com/en/physiology/the-renin-angiotensin-aldosterone-system/)
- [Long-term blood pressure control by the kidney](https://durgical.com/en/physiology/long-term-blood-pressure-control-by-the-kidney/)
- [Flow, pressure and resistance: Poiseuille and turbulent flow](https://durgical.com/en/physiology/flow-pressure-and-resistance-poiseuille-and-turbulent-flow/)

## Connections

## Related 4

- [Arteriosclerosis: the three patterns](https://durgical.com/en/general-pathology/arteriosclerosis-the-three-patterns/)
- [Hypertensive heart disease and cor pulmonale](https://durgical.com/en/general-pathology/hypertensive-heart-disease-and-cor-pulmonale/)
- [Aortic dissection](https://durgical.com/en/general-pathology/aortic-dissection/)
- [Vascular anomalies: berry aneurysm, AV fistula, fibromuscular dysplasia](https://durgical.com/en/general-pathology/vascular-anomalies-berry-aneurysm-av-fistula-fibromuscular-dysplasia/)

## Related conditions 10

- [Arterial hypertension](https://durgical.com/en/conditions/arterial-hypertension/)
- [Renovascular hypertension (renal artery stenosis)](https://durgical.com/en/conditions/renovascular-hypertension/)
- [Primary hyperaldosteronism (Conn syndrome)](https://durgical.com/en/conditions/primary-hyperaldosteronism/)
- [Phaeochromocytoma](https://durgical.com/en/conditions/phaeochromocytoma/)
- [Cushing syndrome](https://durgical.com/en/conditions/cushing-syndrome/)
- [Coarctation of the aorta](https://durgical.com/en/conditions/coarctation-of-the-aorta/)
- [Preeclampsia](https://durgical.com/en/conditions/preeclampsia/)
- [Obstructive sleep apnoea](https://durgical.com/en/conditions/obstructive-sleep-apnoea/)
- [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/)
- [Hypertensive emergency and urgency](https://durgical.com/en/conditions/hypertensive-emergency-and-urgency/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [High Blood Pressure | Hypertension | MedlinePlus](https://medlineplus.gov/highbloodpressure.html) (MedlinePlus, US National Library of Medicine, 2025); [Pheochromocytoma](https://www.ncbi.nlm.nih.gov/books/NBK589700/) (StatPearls (NCBI Bookshelf), 2025).

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