The human body has two renal arteries that supply blood to the kidneys. One artery supplies the left kidney and one the right. As the primary vascular supply for these organs, the renal arteries carry a large percentage of the total blood flow. Between one-fourth and one-third of the heart’s output passes through them before the kidneys filter it.
Each renal artery is about 4 to 6 centimeters long and 5 to 6 millimeters in diameter. They connect to the abdominal aorta, which begins at the diaphragm. They enter the renal hilum, an opening in the front of the renal pelvis, at the inner concavity of each kidney. The arteries then split into two main branches. These branches split into smaller arterioles inside each kidney that deliver blood to the microscopic nephrons.
Both renal arteries connect to the abdominal aorta at the L1 and L2 vertebral body level, below the superior mesenteric artery connection to the abdominal aorta. The right renal artery starts in the front and to the side of the aorta, then runs a lower course behind the inferior vena cava to the right kidney. The left renal artery starts at a slightly higher point of the aorta but has a more lateral position. Its course is much shorter than that of the right renal artery and runs in a near-horizontal position to the left kidney.
Oxygenated, mineral-rich blood travels to the kidneys through the right and left renal arteries. When the average person is at rest, the renal arteries deliver about 1.2 liters of blood to the kidneys each minute. This blood provides both cellular respiration and nutrition. But the renal arteries have other functions as well. Blood flows through the renal arteries, then through the arterioles at very high pressure. The arteries contain sensory receptors in their smooth muscle walls which respond to pressure changes. When blood pressure varies, the arteries either expand or contract to maintain a constant blood flow volume.
Arteries carry oxygenated blood from the heart, while veins bring oxygen-depleted blood back. As the renal arteries deliver blood to the kidneys for filtering, the renal veins remove the filtered blood and transport them to the inferior vena cava. Each vein has two parts. The posterior veins help drain the back sections of the kidneys, while the anterior veins help with the front sections. The left renal vein runs between the aorta and the superior mesenteric artery, then joins with the inferior vena cava. It passes in front of the aorta. The right renal vein is near the front of the right renal artery and is shorter than the left vein.
Nephron development occurs into the later gestational stages of fetal development. The fetus transfers urine through the ureters from the kidneys to the bladder and excretes it into the amniotic sac. As the fetus’ torso grows, the kidneys move upwards and rotate, resulting in longer ureters. Several transitory vessels originating from the aorta supply the growing kidneys. During the kidneys’ ascent, the renal arteries emerge from the lumbar region of the aorta and the transitory vessels disappear.
Renal arteries are known as end arteries because they do not connect with their adjacent branches. This means they are the only supply of blood to the kidneys. They first divide close to the hilum into five segmental arteries:
The right renal artery is the longer vessel and passes behind the inferior vena cava. Before the renal artery enters the hilum, it splits into two branches: the inferior suprarenal artery and the ureteric branch.
Between 25 and 40% of people have unique renal artery anatomy. Of those variations, about 30% are accessory renal arteries and are fairly common. In most cases, two or more renal arteries develop on the left side. They arise from the aorta, just above or below the main renal artery and follow it to the renal hilum. These abnormalities may cause concern if they result in errors during an operation such as a kidney transplant. Pain is a symptom of an accessory renal artery, along with the usual symptoms associated with urinary tract infections.
Sufficient blood pressure is essential to healthy kidney function and crucial for keeping kidney tissue alive. Both the renal arteries and the arterioles must maintain the blood flow for this to happen. Adequate blood flow is also vital for the process of separation of waste from the blood. If the blood flow occurs in one of the segmental arteries or one of the branches, kidney tissue can die. Blood flow interruption to the entire kidney causes kidney failure.
High blood pressure, when uncontrolled, can cause the renal arteries to narrow, weaken, or harden. This prevents them from delivering blood to the kidney tissue, which can damage the kidneys and impact their ability to filter the blood. Additionally, oxygen and nutrients cannot reach the nephrons, rendering the kidneys unable to regulate fluid, acids, salts, and hormones in the body. A condition called renal artery stenosis occurs when plaque accumulates in the renal arteries, blocking the flow of blood to the kidneys. If the narrowing is greater than 60 to 70%, doctors may perform angioplasty with stent placement to increase blood flow.
If a physician suspects an issue with the renal artery, such as renal artery stenosis, the first step is a physical examination. He or she will place a stethoscope around the kidney area to listen for sounds that might suggest a narrowing or blocking of the artery. The physician may also perform blood and urine tests. Additional diagnostic testing, such as Doppler ultrasound, computerized tomography (CT) scan, or magnetic resonance angiography (MRA) will help determine a diagnosis. In some cases, the physician may inject a dye into the renal arteries to define blood flow more clearly, then perform an X-ray examination.
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