Regulation of renal blood flow

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Regulation of renal blood flow


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Regulation of renal blood flow

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A 26-year-old man is brought to the emergency department to evaluate his altered mental status after being found down while working outdoors on a hot sunny day. He had two episodes of non-bloody, nonbilious emesis before arrival. His temperature is 40°C (104°F), pulse is 130/min, respirations are 17/min, and blood pressure is 70/50 mmHg. Mucous membranes are dry. Which of the following changes will likely be observed in the glomerular function of this patient?  

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Effective renal plasma flow p. 606, 733

Renal blood flow (RBF) p. 604, 736

acute injury and p. 626

endocrine function and p. 613

NSAID effects on p. 613

renal plasma flow and p. 606

Renal plasma flow p. 606

glomerular dynamics and p. 607


The kidneys’ main job is to filter the blood to remove the waste - so it shouldn’t be surprising that they receive about a quarter of the blood that the heart pumps with each beat.

On average, the heart pumps out almost 5 liters of blood every minute, so one-quarter of that - or 1.25 liters - flows into the renal artery every minute.

Blood from the renal artery flows into smaller and smaller arteries, eventually reaching the tiniest of arterioles called the afferent arterioles.

After the afferent arteriole, blood moves into a tiny capillary bed called the glomerulus.

The glomerulus is part of the functional unit of the kidney, called the nephron.

There’s about 1 million nephrons in each kidney, and each of them consists of a renal corpuscle - made up of the glomerulus and the Bowman’s capsule surrounding it - and a renal tubule.

Interestingly, once the blood leaves the glomerulus, it does not enter into venules.

Instead the glomerulus funnels blood into efferent arterioles which divide into capillaries a second time.

These capillaries are called peritubular capillaries - because they are arranged around the renal tubule.

Now, blood filtration starts in the glomerulus, where an urine precursor called filtrate is formed.

The amount of blood filtered into the nephrons by all of the glomeruli each minute is called the glomerular filtration rate, and it’s actually just a small fraction of the blood that gets to the kidneys, because the glomerulus doesn’t allow red blood cells and proteins to pass through and be excreted into urine.

So right from the start, what passes through the glomerulus is mostly plasma - which normally makes up about 55% of blood.

What is more, the glomerulus only filters about 20% of that plasma in one go.

So when all is said and done, of those around 1.25 liters that the heart pumps out every minute, glomerular filtration rate is normally around 125 milliliters. This filtrate then enters the renal tubule.

The renal tubule is made up of a proximal convoluted tubule, the nephron loop - also known as the loop of Henle - which has an ascending and a descending limb - and finally the distal convoluted tubule.


Renal blood flow is regulated by the autonomic nervous system, hormones, and local autoregulation mechanisms. The autonomic nervous system, primarily the sympathetic nervous system, can increase or decrease renal blood flow by constricting or dilating renal arterioles. This is accomplished by the release of certain hormones. For example, adrenaline and angiotensin II increase arteriolar resistance and decrease renal blood flow, whereas atrial and brain natriuretic peptide decrease arteriolar resistance and increase renal blood flow. In autoregulation, the kidneys keep blood flow and the glomerular filtration rate constant, even when the blood pressure range changes.


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Purinergic signaling in inflammatory renal disease" Frontiers in Physiology (2013)
  6. "Intrarenal Purinergic Signaling in the Control of Renal Tubular Transport" Annual Review of Physiology (2010)
  7. "Interactions between adenosine, angiotensin II and nitric oxide on the afferent arteriole influence sensitivity of the tubuloglomerular feedback" Frontiers in Physiology (2013)
  8. "Adenosine A2 receptors modulate tubuloglomerular feedback" American Journal of Physiology-Renal Physiology (2010)

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