68 75 Nephritic blood flow

Renal blood flow: about 20% of cardiac output, glomerular filtration, autoregulation and acute kidney injury.

Renal blood flow is remarkably high for the size of the kidneys: two organs weighing together only about 300 g receive about 20% of cardiac output at rest, roughly 1 L/min. This large flow is not needed for the kidneys' own oxygen supply but for their function: filtering the blood. About 180 litres of plasma are filtered each day, from which the kidneys reabsorb water, salts and nutrients and excrete waste. Kidney blood flow is closely linked to blood pressure regulation through the renin–angiotensin–aldosterone system.

KidneyFiltrationBlood pressure

Share of cardiac output≈ 20%

At rest≈ 1 L/min

Glomerular filtration≈ 120 mL/min (≈ 180 L/day)

Hormonal linkrenin–angiotensin–aldosterone

Figure 1. Resting distribution of a cardiac output of about 5 L/min (after Chapman and Mitchell, 1965). The highlighted bar shows renal blood flow.

This application estimates regional blood flow as a percentage of cardiac output and converts it into mL/min from the calculated cardiac output. In clinical practice, organ blood flow is measured invasively or with imaging (for example indicator dilution, Doppler ultrasound, PET or MRI perfusion).

Regulation

Through autoregulation (the myogenic response and tubuloglomerular feedback), the kidneys keep their blood flow and filtration fairly stable over a wide range of blood pressures. When pressure or volume falls, the kidneys release renin; angiotensin II constricts vessels and aldosterone retains salt and water. In shock, sympathetic nerves strongly reduce renal flow to protect the heart and brain, at the cost of kidney function.

Clinical significance

Acute kidney injury: low renal flow in shock, dehydration, bleeding, heart failure or sepsis reduces filtration and urine output; prolonged hypoperfusion damages the tubules
Renal artery stenosis: narrowing (atherosclerosis, fibromuscular dysplasia) activates renin and causes hypertension
Medicines that reduce renal flow or autoregulation (NSAIDs, ACE inhibitors and ARBs in dehydration, contrast agents) can impair kidney function, especially in older people
Chronic kidney disease develops with long-standing hypertension and diabetes, which damage small renal vessels

Seek emergency care

for very little or no urine, especially with dehydration, low blood pressure, swelling or confusion.

References

Singer M, Deutschman CS, Seymour CW, et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA. 2016;315(8):801–810. doi:10.1001/jama.2016.0287
Vander A, Sherman J, Luciano D. Human Physiology: The Mechanisms of Body Function. 8th ed. Boston: McGraw-Hill; 2001. Fig. 14-9 (after Chapman CB, Mitchell JH. Sci Am. 1965). Data: BioNumbers BNID 109465

This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

Published on 30 April 2024