The Interlobular Veins Are Parallel and Travel Alongside the Renal Arteries
Interlobular veins run parallel to and alongside the renal arteries found in each kidney lobe. They receive blood from arcuate arteries that run along the corticomedullary junction, along with their respective artery which drains into the inferior vena cava and supplies direct supply to adrenal glands and ureters.
The arterial and venous blood flow to the kidneys is directed toward glomeruli (afferent, or “toward”) and away from nephrons (efferent, or “exit”) in a countercurrent exchange system.
At first, blood from afferent arterioles enters the glomerulus under high pressure. This promotes filtration of materials absorbed from collecting tubules by splitting plasma and solutes into constituent parts that are then filtered out through its fenestrated capillaries and filtration slits.
Once in the glomerulus, blood from afferent arteries travels down its tuft into each nephron’s capillary bed, creating an intricate network surrounding glomerular capillaries (Figure 2; see Figure 11-7). These tufts are then encircled by peritubular capillaries to form a peritubular capillary plexus.
Peritubular capillaries are linked by a network of venous blood vessels to the glomeruli and nephrons. These loop-shaped vessels passively exchange ions and solutes according to concentration gradients, helping reduce washout of interstitial osmolality by both the nephrons as well as by the glomerular tufts themselves.
However, some material does escape through the glomerular tufts into collecting tubules and return to the general circulation. This is an entirely normal occurrence and an integral part of glomerular filtration.
The efferent arterioles of the outer, midcortical and juxtamedullary glomeruli divide again to form a network of peritubular capillaries around collecting tubules and the nephron’s cortex (Figure 2; see Figure 11-7). This afferent glomerular circulation serves as a portal system as the glomerular tufts reunite into an efferent arteriole that runs for some distance before rejoining with its counterpart to form an extensive capillary bed covering portions of the nephron’s cortex (Figure 11-7).
At the intersection of the cortex and medulla, afferent arteries bend over to form an arch called an arcuate artery. This supplies blood from radial arteries to the glomeruli and nephrons. Numerous short lateral branches known as afferent arterioles branch off from this central artery to nourish these same glomeruli with blood.
Small arteries contain layers of muscular cells within their walls. When these arteries are small, this layer may be hard to discern.
There are also some arteries without a muscular layer, commonly referred to as afferent arteries or interlobular arteries.
The afferent arteries branch at right angles from the arcuate artery and supply blood to the glomeruli. Unfortunately, they are susceptible to focal ischemic necrosis (infarct), like any organ with end arteries since they lack anastomoses.