RENAL BLOOD FLOW

Vascular supply to the kidney (normal anatomy)
Infarction
Contribution of renal blood supply to pathogenesis of renal lesions
Morphology of lesions and differential diagnosis

An understanding of the renal vasculature will facilitate understanding the pathogenesis of many diseases which occur in the kidney.

VASCULAR SUPPLY TO THE KIDNEY (normal anatomy)

The kidney is supplied with blood via the renal arteries that branch directly from the aorta, and enter the kidney at the hilus.

The INTERLOBAR ARTERY is the first branch of the renal artery.

The ARCUATE arteries (which arise from the interlobar arteries) run along the cortico-medullary junction and can be seen on cross section in histologic renal sections.

Since this vessel courses through the cortico-medullary junction in the shape of an "ARC", it is called the ARCUATE ARTERY.

The arcuate arteries give rise to the INTERLOBULAR arteries which then supply the glomeruli via AFFERENT arterioles.

Do you see the small branches leaving the interlobular artery? These are the INTRALOBULAR arteries which become the afferent arterioles.

Remember that the afferent arteriole brings blood to the glomerulus and the efferent arteriole takes blood away from the glomerulus.

The efferent arterioles either 1) carry blood to capillaries in the medulla (Vasa recta) or 2) form anastomotic capillaries in the cortex (peritubular plexus).

Efferent arterioles of glomeruli in the outer cortex form the peritubular plexus which surrounds proximal and distal tubules.

Efferent arterioles of glomeruli in the deeper cortex contribute to the adjacent peritubular plexus and also form the vasa recta which accompany the loop of Henle into the medulla.

QUESTION: Can you think of 2 functions of the Vasa recta? Click to see answer!
ANSWER: The vasa recta provide nourishment (nutrients and oxygen) to the associated tubules. In addition, the vasa recta are the vascular component of the counter-current mechanism.

Arteriole sphincters

There are "feedback" mechanisms which regulate glomerular filtration and blood flow in each nephron as shown in this schematic.

Efferent and afferent arterioles constrict and dilate to control blood flow to the glomerulus.

QUESTION: Would GFR be increased or decreased with the dilation of the afferent arteriole and constriction of the efferent arteriole? Click to see answer!
ANSWER: GFR would increase because as the afferent arteriole dilates, more blood enters the glomerulus. As the efferent arteriole constricts, the filtration pressure would increase and filtrate would enter the proximal tubule.

Would GFR be increased or decreased with the constriction of the afferent arteriole and dilation of the efferent arteriole? The GFR would DECREASE because filtration pressure decreased.

QUESTION: Could blood flow be diverted from specific nephrons? Click to see answer!
ANSWER: Note that constriction of the afferent arteriole would prevent blood from entering the glomerulus. That glomerulus would thus not be involved in filtration. Blood flow in the kidney can be "shunted" from one area to another (cortical nephrons to the juxtamedullary nephrons). This mechanism of shunting will occur when renal blood flow is reduced (as in shock).

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