Renal blood flow must be regulated so the kidneys can filter blood at an appropriate rate. Changes in renal blood flow affect the amounts of solutes and water retained or discarded, which in turn influence blood osmolarity and blood pressure.
The kidneys receive sympathetic innervation through the celiac plexus and splanchnic nerves. During resting conditions, relatively low sympathetic activity allows vasodilation and supports blood flow through the kidneys.
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What happens to renal blood flow when sympathetic activity rises?
Norepinephrine and epinephrine promote afferent arteriole vasoconstriction. This reduces blood flow into the glomeruli and lowers filtration, helping redirect blood during stress.
What is renal autoregulation?
Renal autoregulation is the kidney’s ability to keep blood flow and filtration relatively stable despite changes in systemic blood pressure. The myogenic mechanism and tubuloglomerular feedback contribute to it.
How does the myogenic mechanism respond to pressure changes?
Increased pressure stretches afferent arteriole smooth muscle, causing it to contract and resist increased flow. Reduced pressure allows the muscle to relax, lowering resistance.
How do ATP and adenosine affect the afferent arteriole when GFR rises?
Higher GFR increases NaCl delivery and flow sensed by macula densa cells. These cells release more ATP and adenosine, which promote afferent arteriole constriction and help reduce GFR.
What is the role of NO in tubuloglomerular feedback?
NO relaxes the afferent arteriole, counteracting the constricting influence of ATP and adenosine. It helps fine-tune local control of GFR.
Quiz questions
Which renal arteriole is directly constricted by increased sympathetic activity to reduce glomerular blood flow?Answer: The afferent arteriole.
What is one effect of aldosterone in the response to reduced blood pressure?Answer: It increases Na⁺ and water retention, helping to increase blood volume.
How does the afferent arteriole respond to increased blood pressure through the myogenic mechanism?Answer: Its smooth muscle contracts, increasing resistance and limiting the rise in renal blood flow.
A rise in GFR increases NaCl delivery to the macula densa. What response helps bring GFR back down?Answer: The macula densa increases ATP and adenosine signaling, promoting afferent arteriole constriction.
How does nitric oxide influence the local control of GFR?Answer: It relaxes the afferent arteriole and opposes the constricting effects of ATP and adenosine.
Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.