The organs of the human body all need the supply of blood, because there is nutrients and oxygen in the blood that supply the life of the organ, and the blood can take away the metabolites produced by the metabolism of the organs, and the blood is transported by the blood vessels. The renal arteries are arterial blood that contains oxygen to the kidneys, and the renal veins are used blood from the kidneys to be taken out of the kidneys. The renal arteries, renal veins, renal pelvis, and associated structures entering and leaving the kidney are encased in connective tissue, collectively referred to as the renal pedicle.
Fig. 1: Dark red is the renal artery; blue is the renal vein, and light red is the renal ureter.
Renal arteries
The renal artery is a branch of the abdominal aorta that branches between the flat L1 and L2 vertebral bodies. Since the abdominal aorta is left and the inferior vena cava is to the right, the right renal artery is longer and passes behind the inferior vena cava.
After the renal artery separates from the aorta, it continues to produce branches that nourish the adrenal glands, arenal pelvis, and proximal ureter. After the main trunk of the renal artery enters the renal portal, it is divided into branches of the arterial arteries that are independent of each other and do not anastomose, and nourish different areas of the kidney. Therefore, obstruction or damage to the renal artery will lead to segmental renal infarction rather than full renal infarction.
Figure 2: Renal artery branches supply different areas of the kidney
Renal arteries can usually be divided into anterior and posterior trunks. The anterior stem roughly supplies the first 2/3 of the kidneys, and the posterior trunk supplies 1/3 of the kidneys. Normally (regardless of vascular variation), the anterior trunk is divided into four renal arterial branches: the apex, upper, middle, and lower; the posterior renal artery is the first and most constant branch of the renal artery (low variability) that emanates from the renal artery before entering the renal portal. The posterior artery emanating from the posterior trunk enters the renal parenchyma from the posterior side of the renal pelvis, while the other renal arteries enter from the front of the renal pelvis. If the posterior arterial branch is deformed from the front of the ureter, it may lead to obstruction of the renal pelvisal junction (UPJO).
Vascular variation in the kidneys is very common, and according to statistics, 25% to 40% of kidneys have anatomical variations of renal vascularities. The number of renal arteries is the most common variant, with the left side being more common. After the renal artery separates from the abdominal aorta, it branches out in advance before entering the renal gate. Some variants may also be separated from the vertebral positions seen in T1 and L4, supplying directly to the kidneys. Rarely, it may also originate in the hip artery or superior mesenteric artery. According to statistics, 25% to 28% of patients have this adrenal artery, and it is considered to be the only arterial supply in a specific area of the kidney, which can supply the inferior pole and occasionally the upper renal pole area. These variants are usually harmless in normal people, but they are meaningful in surgical patients, and should be carefully evaluated before surgery, such as kidney transplantation, nephrectomy, etc., to avoid intraoperative bleeding.
Between the posterior and anterior arteries of the posterior renal segment, i.e. the area of the lateral posterior side of the kidney, there is a longitudinal vascular-free plane (Brodel line), along which the kidney is incised, and bleeding is reduced. This area has also become an entry route option for many renal surgeries, reducing renal bleeding, such as the posterior calyx along the Brodel line during percutaneous renal puncture, which is preferred for puncture, and non-atrophic nephrotomy, which can also be incised from this non-vascular plane.
There may also be individual differences in the position of this plane, which in some cases may be identified by preoperative angiography or intraoperative renal arterial injection of methylene blue.
After the renal artery enters the renal sinus, each segment of the artery continues to separate the lobe artery, and the lobe artery enters the renal parenchyma and further divides the interlobeal artery, which extends through the renal column to the periphery of the kidney, forming a bow artery at the bottom of the renal pyramid at the junction of the skin and marrow. These interlobular arteries radiate from the arch artery and eventually form glomerular arteries, including the incisor arterioles and the bulbous arterioles. Each arteriole forms one glomerular, and there are about 2 million glomeruli in the human body (about 1 million unilateral kidneys). Blood is filtered through the glomeruli, and the filtrate leaves the arterial system and collects in the bowman sac to form a prouria, which forms the final urine after reabsorption and secretion of the renal tubules and collection ducts. Blood flows back from the glomeruli through the efferent arteries of the glomeruli and then descends into the renal medulla into the renal medulla around the renal tubules in the renal cortex.
The arteries supplying the kidneys are gradually divided into: renal artery renal segment artery lobular artery interlobite artery lobular interlobite artery into the glomerular arteriolelet.
Renal veins
The role of the renal vein is similar to that of other organ veins, mainly the blood flowing back to the kidney, there is a wide range of venous plexus in the kidney to recover blood, and finally the synthesis of renal veins is returned to the inferior vena cava. Venous return of the kidney has extensive collateral venous circulation, so the venous branches of the renal segment are obstructed and occluded, and their impact on renal venous return is small.
Glomerular capillaries merge into interlobular veins, which are freely formed by the subcapular plexus of stellate veins and perirenal veins. The interlobular veins continue to converge to form to the toxoplain veins, interlobeal veins, leaf veins, and renal veins, which are accompanied by the corresponding arteries, and finally three to five renal veins eventually converge to form renal veins.
Figure 3: Left renal venous return and collateral circulation
The inferior vena cava is more right- and therefore the length of the left and right renal veins is different, with the right renal vein 2 to 4 cm long and the left renal vein 6 to 10 cm long. The left renal vein also receives a return from the left adrenal vein and the left gonadal (testicle or ovarian) vein, which is also a cause of male infertility after varicocele on the left, and adrenal hormones and metabolites affect the gonads through the left gonadal vein.
The left renal vein passes through the sharp angle between the superior mesenteric artery and the front of the aorta, and if the angle is too small, it will affect the reflux of the left renal vein, resulting in nutcracker syndrome, which is one of the reasons why the left spermatic vein is more prone to varicose, which is more likely to occur in emaciated adolescents.
The left renal vein can also receive a return from the lumbar vein, which may be torn during surgical procedures in the left renal vein.
In terms of vascular variation, pararenal veins also occur in a certain proportion, with the left side usually located behind the aorta, while the paraneal veins on the right side are more likely to occur. The most common variant of the left renal venous system is the cyclic aortic left renal vein, which occurs in 2% to 16%. Presents with left renal veins bifurcated into lateral branches on the ventral and dorsal sides that surround the abdominal aorta. In the left renal vein behind the aorta, a single left renal vein crosses from the back of the aorta and joins the lumbar segment of the inferior vena cava.