Renal Blood Flow Regulation Notes
Osmosis High-Yield Notes
This Osmosis High-Yield Note provides an overview of Renal Blood Flow Regulation essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Renal Blood Flow Regulation:
NOTES NOTES RENAL BLOOD FLOW REGULATION RENAL BLOOD FLOW REGULATION osms.it/renal-blood-flow-regulation ▪ Blood enters kidney via renal artery, leaves via renal vein ▫ Blood enters glomerulus via afferent arteriole, leaves via efferent arteriole ▪ Renal blood ﬂow: volume of blood that reaches kidneys in unit time; determined by pressure gradient (pressure in renal artery pressure in renal vein) divided by arteriolar resistance ▫ ↑ blood pressure → ↑ pressure in renal artery → ↑ renal blood ﬂow ▫ ↓ arteriolar resistance → ↑ renal blood ﬂow ▪ Renal blood ﬂow determines glomerular ﬁltration rate (GFR) ▫ ↑ renal blood ﬂow → ↑ GFR ▪ Regulation of renal blood ﬂow: increasing/ decreasing arteriolar resistance Key hormones: increasing arteriolar resistance (decreasing renal blood ﬂow) ▪ Adrenaline (epinephrine) ▫ Secreted by adrenal gland in response to sympathetic stimulation ▫ Binds to alpha-1 adrenergic receptors along afferent, efferent arterioles → smooth muscle cells contract ▪ Angiotensin II ▫ Renin produced by juxtaglomerular cells in afferent arteriole → released into blood, becomes angiotensin I in response to low blood pressure → converted into angiotensin II by angiotensin-converting enzyme (ACE), synthesized in endothelial cells (esp. in lungs) 530 OSMOSIS.ORG ▫ Binds to angiotensin receptors along afferent, efferent arterioles → smooth muscle cells contract ▫ Efferent arterioles more sensitive to angiotensin II → constrict more → blood builds up in glomerulus → GFR constant ▫ High levels of angiotensin II → afferent arterioles constrict equally → ↓ GFR Key hormones: decreasing arteriolar resistance (increasing renal blood ﬂow) ▪ Atrial natriuretic peptide ▫ Secreted by atria of heart in response to increased cardiac workload ▫ Binds to natriuretic peptide receptors along afferent, efferent arterioles → smooth muscle cells relax ▪ Brain natriuretic peptide ▫ Secreted by ventricles of heart in response to increased cardiac workload ▫ Binds to natriuretic peptide receptors along afferent, efferent arterioles → smooth muscle cells relax ▪ Prostaglandins (e.g. prostaglandin E2, I2) ▫ Produced by kidneys in response to sympathetic stimulation ▫ Binds to prostaglandin receptors along afferent, efferent arterioles → smooth muscle cells relax ▫ Prevents kidney damage during sympathetic stimulation ▪ Dopamine ▫ Synthesized in brain, kidneys ▫ Binds to dopaminergic along afferent, efferent arterioles → smooth muscle cells relax
Chapter 60 Renal Physiology: Renal Blood Flow Regulation AUTOREGULATION OF RENAL BLOOD FLOW ▪ Keeps renal blood ﬂow, GFR constant over range of systemic blood pressures (80– 200mmHg) ▫ 80mmHg: smooth blood cells in arterioles completely relaxed, renal blood ﬂow optimal ▫ Systemic blood pressure increases → smooth blood cells contract to maintain optimal renal blood ﬂow Mechanisms for autoregulation ▪ Myogenic mechanism: smooth muscle cells in arterioles automatically contract when stretched by high blood pressure (related to increased renal blood ﬂow) ▪ Tubuloglomerular mechanism: macula densa cells release adenosine → increases resistance in afferent arteriole when more sodium, chloride ions detected in distal convoluted tubule (related to increased GFR, renal blood ﬂow) Figure 60.1 Graph displaying the relationship between systolic blood pressure and renal blood ﬂow. The kidneys achieve consistency between 80–200mmHg by adjusting their own arteriole resistance. Figure 60.2 The region where the distal convoluted tubule and the afferent arteriole are close to one another is called the juxtaglomerular apparatus. This proximity allows adenosine from the macula densa cells to diffuse over to the juxtaglomerular cells of the afferent arteriole, alerting them to ↑ GFR. This increases arteriolar resistance → ↓ GFR. OSMOSIS.ORG 531
MEASURING RENAL PLASMA FLOW & RENAL BLOOD FLOW osms.it/measuring-renal-plasma-blood-flow ▪ Fick principle: amount of substance in blood that ﬂows into organ = amount that ﬂows out (if organ doesn’t produce/degrade that substance) True renal plasma ﬂow ▪ Add para-aminohippuric acid (PAH) to body (isn’t made in body, doesn’t affect renal function) ▪ Fick principle: amount of PAH that ﬂows into kidneys through renal artery = amount of PAH that ﬂows out (through urine, renal veins) ▫ Inwards ﬂow of PAH = outwards ﬂow of PAH ▫ [PAH]artery x renal plasma ﬂow = ([PAHvein x renal plasma ﬂow) + ([PAHurine x urine ﬂow) ▫ Renal plasma ﬂow x ([PAH]artery - [PAH] ) = [PAH]urine x urine ﬂow vein [PAH ]urine × Urine flow Renal plasma flow = [PAH ]artery − [PAH ]vein ▫ Effective renal plasma ﬂow ▪ Two assumptions ▫ 90% of PAH leaves kidneys in urine → 10% leaves in renal vein negligible ▫ Concentration of PAH in renal artery = concentration of PAH in any peripheral vein Effective renal plasma flow = [PAH ]urine × Urine flow [PAH ] ▪ ▪ Effective renal plasma ﬂow = 90% of true renal plasma ﬂow Renal blood ﬂow ▪ Renal blood flow = Renal plasma flow (1− hematocrit) ▫ Hematocrit: blood volume fraction occupied by red blood cells (i.e. fraction of blood volume not plasma) ▪ Measure concentration of PAH in renal artery/vein, urine; measure urine ﬂow Figure 60.3 Para-aminohippuric acid (PAH) is used to measure effective renal plasma ﬂow. It is assumed that about 90% of PAH that enters kidneys through renal artery is excreted in urine, and only 10% enters the renal vein → ignore this, assume that effective renal plasma ﬂow = 90% of true renal plasma ﬂow. 532 OSMOSIS.ORG
Osmosis High-Yield Notes
This Osmosis High-Yield Note provides an overview of Renal Blood Flow Regulation essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Renal Blood Flow Regulation by visiting the associated Learn Page.