Renal Blood Flow Flashcards
Major arteries supplying kidneys
Renal artery → Segmental arteries → Interlobar arteries → Arcuate arteries → Interlobular arteries → Afferent arterioles
Venous drainage of kidneys
Peritubular capillaries & vasa recta → Interlobular veins → Arcuate veins → Interlobar veins → Renal vein → IVC
Why is the kidney susceptible to hypoxic damage?
Medullary circulation is sluggish, making it vulnerable to ischemia in shock
Methods to measure RBF
PAH clearance method, Doppler ultrasound
PAH clearance method formula
ERPF = (U_pAH × V) / P_pAH, then RBF = ERPF / Extraction Ratio (0.9)
Myogenic mechanism in RBF
Afferent arteriole constricts when BP is high, dilates when BP is low
Tubuloglomerular feedback
Macula densa detects NaCl, causing vasoconstriction if high, vasodilation & renin release if low
Sympathetic effect on RBF
Vasoconstriction → Decreased RBF & GFR, extreme activation can cause ischemia
Angiotensin II effect on RBF
Preferentially constricts efferent arteriole, maintaining GFR despite low RBF
Vasodilators of RBF
Prostaglandins, NO, ANP, Dopamine (low dose)
NSAID effect on RBF
Blocks prostaglandins → Afferent vasoconstriction → Reduced RBF & GFR → Risk of AKI
Renal autoregulation mechanisms
Myogenic response, Tubuloglomerular feedback, Stable RBF between 80-180 mmHg
What percentage of cardiac output does the kidney receive?
About 20-25% of cardiac output, despite being only ~0.5% of body weight.
Why is renal blood flow (RBF) unique compared to other organs?
Kidney has two capillary beds in series: Glomerular capillaries (high-pressure filtration) & Peritubular capillaries (low-pressure reabsorption).
What is the significance of the high glomerular capillary pressure?
Facilitates ultrafiltration of plasma into Bowman’s space, forming the primary filtrate.
Why does renal circulation have a high oxygen shunting effect?
Oxygen can bypass tissue exchange by diffusing between closely arranged arterial & venous vessels, reducing O2 delivery to deeper renal structures.
What is the difference in blood supply between the renal cortex and medulla?
Cortex receives ~90% of RBF, while the medulla receives only ~10%, making the medulla more susceptible to hypoxia.
Why is the renal medulla vulnerable to ischemia?
Medullary circulation is slow, has low oxygen delivery, and is highly dependent on vasodilators like prostaglandins.
How does renal autoregulation maintain RBF?
Through myogenic response (arteriole constriction/dilation) and tubuloglomerular feedback (TGF) via macula densa sensing NaCl levels.
What happens to RBF during sympathetic stimulation?
Strong activation (e.g., shock, stress) causes afferent arteriole vasoconstriction, reducing RBF and risking ischemia.
How does angiotensin II affect RBF?
Preferentially constricts efferent arteriole, maintaining glomerular filtration rate (GFR) even when RBF is low.
Why does NSAID use affect renal blood flow?
Blocks prostaglandins that normally dilate afferent arterioles → Reduced RBF → Risk of acute kidney injury.
What is the role of nitric oxide (NO) in renal circulation?
NO is a vasodilator that maintains normal RBF. Endothelial dysfunction (e.g., in hypertension) can reduce NO, leading to renal vasoconstriction.
Why is renal blood flow (RBF) important for excretion?
High RBF allows efficient filtration of metabolic wastes and toxins while maintaining electrolyte balance.
