The renal arteries are blood vessels that deliver oxygenated blood from the aorta to the kidneys. These arteries supply the blood necessary for filtration and waste removal, supporting kidney function. Understanding their anatomical structure helps comprehend how the kidneys receive their blood supply.
External Pathway: Where Renal Arteries Begin
The main renal arteries originate directly from the abdominal aorta. They emerge at the level of the first or second lumbar vertebrae, just below the superior mesenteric artery. Each kidney receives one artery, which extends horizontally towards the kidney’s medial indentation, known as the hilum.
Due to the abdominal aorta’s position slightly to the left of the midline, the right renal artery is longer than the left. The right renal artery takes a slightly more inferior and oblique path, passing behind the inferior vena cava and the right renal vein to reach the right kidney. In contrast, the left renal artery has a shorter, more horizontal course, lying posterior to the left renal vein.
Internal Network: Branching Within the Kidney
Upon reaching the kidney’s hilum, the main renal artery divides into two major branches: an anterior and a posterior division. These divisions further subdivide into several segmental arteries (arteriae segmentales), which supply specific kidney segments. These segmental arteries are considered “end arteries,” meaning they lack significant connections with other arteries, so blockage in one can affect the supplied kidney tissue.
The segmental arteries then branch into interlobar arteries (arteriae interlobares), which travel between the renal pyramids within the kidney’s columns. As these interlobar arteries reach the junction between the kidney’s outer cortex and inner medulla, they give rise to the arcuate arteries (arteriae arcuatae). These arcuate arteries curve over the bases of the renal pyramids.
Microscopic Circulation: The Smallest Vessels
The arcuate arteries give rise to smaller vessels called cortical radiate arteries (arteriae corticales radiatae), also known as interlobular arteries. These arteries extend outwards into the renal cortex, supplying blood to the outermost region of the kidney. From the cortical radiate arteries, tiny vessels called afferent arterioles (arteriolae afferentes) branch off, each leading to a specialized capillary network called the glomerulus.
The glomerulus is a tuft of capillaries where initial blood filtration occurs. Blood then exits the glomerulus through efferent arterioles (arteriolae efferentes). These efferent arterioles form another capillary network, the peritubular capillaries, which surround the renal tubules in the cortex. In the deeper parts of the kidney, efferent arterioles form specialized straight vessels known as vasa recta, which aid in concentrating urine.
Anatomical Differences Among Individuals
A common variation is the presence of accessory renal arteries, also known as supernumerary renal arteries. These additional arteries, beyond the single main renal artery, supply the kidney. Accessory renal arteries occur in about 20% to 30% of the population and can arise directly from the abdominal aorta or other nearby vessels.
Another variation includes early branching of the main renal artery, where the artery divides into its major branches before reaching the renal hilum. This occurs in approximately 10% of individuals. These anatomical differences are important for surgical planning or medical imaging.