The response to standing up !
- Regulation
- Exam priority: medium
When you stand, blood drops into the legs; fast reflexes speed the heart and tighten the vessels so the brain keeps its supply.
Updated 2026-11-01
Also called: Orthostatic hypotension
See it in 3D: Leg veins · Carotid bifurcation · Aortic arch · Medulla oblongata
What it is
Standing, gravity pools about 500–800 mL of blood in the leg and abdominal veins. Venous return falls, stroke volume drops and arterial pressure tends to fall. Baroreceptors sense it within seconds and the sympathetic system corrects it: heart rate rises, arterioles and veins constrict, and the muscle pump helps. When that response fails, orthostatic hypotension appears.
How it works, step by step
- Gravity raises hydrostatic pressure in the leg veins and they distend with blood.
- Venous return falls, preload drops and stroke volume decreases.
- Pressure falls at the carotid sinus and aortic arch: baroreceptors fire less.
- The vasomotor center raises sympathetic and lowers vagal output within seconds.
- Heart rate and contractility rise, arterioles and veins constrict, and pressure recovers.
- When walking, calf contraction plus the venous valves pushes blood upward (muscle pump).
- If standing goes on, renin–angiotensin–aldosterone and vasopressin retain volume.
Useful values when taking orthostatic vital signs
| Parameter | Value | Note |
|---|---|---|
| Blood shifted to the legs | ≈500–800 mL | |
| Fall that defines orthostatic hypotension | ≥20 mmHg systolic or ≥10 mmHg diastolic | within 3 min |
| Normal heart rate rise | ≈10–20 bpm | |
| Rise that defines POTS | ≥30 bpm | ≥40 bpm in adolescents |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Regulation
- +Baroreceptor reflex (sympathetic ↑, vagal ↓): Corrects pressure within seconds: tachycardia and vasoconstriction.
- +Calf muscle pump and venous valves: Return blood to the chest when walking or tensing the legs.
- +Renin–angiotensin–aldosterone and vasopressin: Retain salt and water if the posture is held.
- −Autonomic neuropathy, beta blockers and vasodilators: Block compensation: dizziness, blurred vision, syncope.
- −Heat and large meals: Divert blood to skin and gut and worsen tolerance.
Clinical notes
- In nursing: measure pressure and pulse lying down after a few minutes, then standing at 1 and 3 minutes; a patient who gets dizzy is a fall risk.
- A soldier standing still in formation can faint: with no muscle pump, blood pools in the legs.
- In hypovolemia orthostatic changes appear before hypotension at rest.
Test yourself
Think of the answer, then tap the question to see it.
Why does standing up reduce stroke volume in the first few beats?
Blood pools in the compliant leg veins, venous return falls and with it left ventricular preload.
A diabetic patient gets dizzy on standing, pressure falls 30 mmHg and heart rate does not change. Which mechanism does this suggest?
Autonomic failure (diabetic neuropathy): the baroreceptor reflex cannot raise sympathetic output, so there is no compensatory tachycardia.
Why can a person standing motionless for a long time faint?
Without muscle contraction the venous pump fails; blood pools in the legs, venous return and output fall, and the brain gets less flow.
Why do orthostatic changes help detect early hypovolemia?
At rest the reflexes still cover the loss, but standing uses up the reserve: marked tachycardia or a pressure fall appears before supine hypotension.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- The baroreceptor reflex
- Nervous control of the circulation and the CNS ischemic response
- Venous return and the Guyton curves
- Vascular compliance and capacitance
- The renin–angiotensin–aldosterone system
Related conditions
In Pharmacology
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 20.4 Homeostatic Regulation of the Vascular System (OpenStax (Rice University), 2022); 20.2 Blood Flow, Blood Pressure, and Resistance (OpenStax (Rice University), 2022); Hypovolemia and Hypovolemic Shock (StatPearls (NCBI Bookshelf), 2025); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 18). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.