Healthy kidneys, illustration. The kidneys filter waste products from the blood. The waste products are transported as urine to the bladder (not seen) via the ureters (brown tubes). On top of each kidney is an adrenal gland, which secretes stress hormones. Down centre are the inferior vena cava (foreground), the body's main vein, and the aorta (background), the body's main artery. The renal arteries branch from the aorta to supply the kidneys with blood. The renal veins carry blood from the kidneys to the inferior vena cava.