The renal arteries are the major blood vessels delivering blood to the kidneys, organs tasked with filtering waste and regulating body fluid balance. The kidneys receive approximately 20% of the heart’s total output, a large volume necessary to maintain the body’s internal chemistry. Understanding the structure of these arteries is foundational to comprehending kidney function and the implications of vascular disease. The arterial network ensures every part of the kidney’s filtering units receives adequate blood flow.
Origin and Initial Path of the Renal Arteries
The paired renal arteries emerge directly from the abdominal aorta, typically situated at the level of the first or second lumbar vertebrae (L1-L2), just below the superior mesenteric artery. Each artery is relatively short. Because the abdominal aorta is on the left and the large inferior vena cava is on the right, the two arteries follow different paths to reach their respective kidneys.
The right renal artery travels a slightly longer and more oblique path, passing behind the inferior vena cava and the right renal vein. In contrast, the left renal artery is generally shorter and follows a more horizontal course, passing only behind the left renal vein. Before entering the kidney, the main artery may give off small branches to the adrenal gland, ureter, and surrounding tissue.
The main artery enters the kidney at the renal hilum, a concave indentation on the medial side. At the hilum, the structures are typically arranged from front to back: the renal vein, followed by the renal artery, and finally, the renal pelvis (which connects to the ureter). As the artery approaches the hilum, it usually divides into two major trunks: an anterior division and a posterior division.
Detailed Branching Within the Kidney
Once inside the renal hilum, arterial blood flow is distributed through a network designed to reach every filtering unit. The main artery’s anterior and posterior divisions immediately branch into five segmental arteries that supply distinct, non-overlapping regions of the kidney parenchyma. These segmental arteries are “end arteries,” meaning they do not significantly connect or anastomose with other segmental arteries, a detail that carries clinical weight.
The segmental arteries then divide into lobar arteries, which give rise to the interlobar arteries. These interlobar arteries travel upward between the renal pyramids, which constitute the kidney’s inner medulla. Reaching the boundary between the inner medulla and the outer cortex, the arteries turn sharply to run parallel to the surface, forming the arcuate arteries.
From the arcuate arteries, the cortical radiate arteries (or interlobular arteries) ascend into the outermost cortex. These vessels supply the nephrons, the microscopic filtering units of the kidney. Tiny branches called afferent arterioles emerge from the cortical radiate arteries, leading directly into the glomerulus, a dense capillary cluster where initial blood filtration takes place.
Common Anatomical Variations
The textbook description of a single renal artery supplying each kidney is not universally true, as the renal arteries are known for anatomical variation. The most frequent deviation is the presence of accessory renal arteries, which occur in about 25% of the population. These extra vessels can be single, double, or multiple.
These accessory vessels often originate directly from the abdominal aorta, though they can rarely arise from other arteries, such as the iliac or mesenteric vessels. They are clinically significant because they do not always enter the kidney through the main hilum; instead, they often enter the kidney directly at the superior or inferior poles. Another variation is early-branching, where the main renal artery divides into its segmental branches much closer to the aorta than is typical, sometimes occurring before it even reaches the hilum.
Clinical Relevance of Renal Artery Structure
Detailed knowledge of renal artery anatomy is necessary for many medical and surgical procedures. The segmental arteries’ status as end arteries means that the blockage of one segmental branch will result in the death of the specific kidney segment it supplies, as there is no backup blood supply. This is a consideration in procedures like partial nephrectomy, where the goal is to remove a diseased portion of the kidney while preserving the healthy tissue.
A common vascular condition is Renal Artery Stenosis (RAS), which is a narrowing of the renal artery, most often caused by atherosclerosis (plaque buildup). The reduced blood flow caused by this narrowing is interpreted by the kidney as low blood pressure. This triggers the release of hormones that lead to renovascular hypertension, a form of high blood pressure that can be difficult to control.
The presence of accessory renal arteries also complicates surgical interventions, particularly kidney transplantation. If an accessory artery is present in a donor kidney, surgeons must carefully connect this second vessel to the recipient’s vasculature to ensure the transplanted kidney receives full blood flow. If an accessory artery crosses the ureter, it can sometimes compress it, potentially leading to an obstruction and fluid buildup in the kidney, which requires surgical correction.