Renal Artery

1. Overview

The renal artery is a paired visceral branch of the abdominal aorta that supplies blood to the kidneys. Each renal artery delivers oxygenated, unfiltered blood to its respective kidney, enabling the filtration, reabsorption, and excretion processes of urine formation. It plays a pivotal role in maintaining systemic blood pressure and electrolyte homeostasis through its regulation of renal perfusion.

2. Location

The renal arteries arise from the abdominal aorta at the level of the L1–L2 vertebrae, just below the origin of the superior mesenteric artery. There are two renal arteries—**right** and left:

• Right renal artery: Longer and passes posterior to the inferior vena cava (IVC) to reach the right kidney.

• Left renal artery: Shorter and travels more directly to the left kidney.

Each renal artery enters the kidney at the hilum, posterior to the renal vein and anterior to the renal pelvis. Before entering the kidney, they typically give off small branches to the adrenal gland (suprarenal artery), ureter, and perirenal fat.

3. Structure

The renal artery is a muscular artery composed of three concentric layers:

• Tunica intima: Lined by endothelium, continuous with the aortic lining.

• Tunica media: Thick layer of smooth muscle and elastic fibers, important for autoregulation.

• Tunica adventitia: Outer connective tissue layer containing sympathetic nerve fibers and vasa vasorum.

Intra-renal branching:

Once inside the kidney, the renal artery branches progressively:

• Segmental arteries → supply specific kidney segments (no collateral circulation)

• Interlobar arteries → run between renal pyramids

• Arcuate arteries → arch over the base of pyramids at corticomedullary junction

• Interlobular (cortical radiate) arteries → extend into cortex and give rise to afferent arterioles

4. Function

The primary function of the renal artery is to deliver a high volume of blood to the kidneys for filtration and urine production. Specific functions include:

• Supply glomeruli: Via afferent arterioles, enabling plasma filtration.

• Support renal parenchyma: Provides oxygen and nutrients to cortex and medulla.

• Enable hormone signaling: Transport hormones (e.g., aldosterone, ADH) to nephrons.

5. Physiological Role(s)

The renal artery contributes to several critical physiological processes:

• Renal perfusion: Approximately 20–25% of cardiac output (~1.2 L/min) is directed through the renal arteries.

• Blood pressure regulation: Renal perfusion pressure affects the renin-angiotensin-aldosterone system (RAAS) via the juxtaglomerular apparatus.

• Autoregulation: Maintains stable glomerular filtration rate (GFR) through mechanisms like the myogenic response and tubuloglomerular feedback.

• Filtration barrier maintenance: Ensures constant pressure for effective plasma filtration across glomerular capillaries.

6. Clinical Significance

Renal Artery Stenosis (RAS)

A condition where the renal artery is narrowed, usually due to atherosclerosis or fibromuscular dysplasia. It leads to:

• Reduced renal perfusion

• Activation of RAAS → secondary hypertension

• Ischemic nephropathy and potential kidney atrophy

Diagnosed with duplex Doppler ultrasound, CT angiography, or MR angiography. May require angioplasty or stenting.

Renal Infarction

Occlusion of the renal artery (e.g., by embolus or thrombosis) causes renal infarction, presenting with sudden flank pain and hematuria. Managed based on cause—anticoagulation or revascularization.

Renal Artery Aneurysm

A rare dilatation of the renal artery which may rupture, thrombose, or cause hypertension. Often asymptomatic and found incidentally on imaging. Surgical repair is considered for large or symptomatic aneurysms.

Accessory Renal Arteries

Present in up to 30% of individuals. These extra renal arteries may arise from the aorta or iliac arteries and enter the kidney at the hilum or directly into the parenchyma. Important to identify before kidney surgery or transplantation.

Renovascular Hypertension

Caused by unilateral or bilateral renal artery stenosis. The ischemic kidney releases excess renin, resulting in refractory hypertension, especially in young or resistant cases. RAAS blockers (e.g., ACE inhibitors) are used with caution in bilateral disease.

Transplantation Considerations

During kidney transplantation, the donor renal artery is surgically anastomosed to the recipient’s external iliac artery. Preoperative imaging assesses the number and course of renal arteries to plan surgery and avoid ischemia.